How to diagnose engine failure due to precat
02-28-2012, 11:43 AM
#1
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Thread Starter
Join Date: Oct 2009
Location: Charlotte,NC
Posts: 174
How to diagnose engine failure due to precat
Guys,
I had another thread talking about my precats failing. My friend told me to stop driving the car, so i did. Havent driven it in about 4 days. I did start it up once, and it was making horrible noises, all from the front cat. I turned it off right away.
Im hoping i didnt kill my engine though.
Thanks
I had another thread talking about my precats failing. My friend told me to stop driving the car, so i did. Havent driven it in about 4 days. I did start it up once, and it was making horrible noises, all from the front cat. I turned it off right away.
Im hoping i didnt kill my engine though.
Thanks
02-29-2012, 06:24 PM
#4
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Join Date: Dec 2011
Location: New Jersey
Posts: 27
P0420 is a code relating to catalyst inefficiency, which in your case is probably due to the front precat disintegrating. I may be off but as far as I know, engine damage due to precats breaking up only occurs during valve overlap or high RPM, when pieces of the cats are sucked back into the cylinder. If you drive the car lightly until the cat problem is resolved, you most likely won't do any damage to the engine itself.
02-29-2012, 07:49 PM
#6
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Join Date: Sep 2008
Location: Connecticut
Posts: 836
There was a thread a long while back about this. A member was talking about several engines he had taken apart. A lot of them had signs of wear that he claimed fit the description of this theory. He defended it rather well if I recall. Naturally, there were still arguments against him. However, with his experience and his presentation of the facts, most people respected what he said. Unfortunately, I do not remember the thread title or the name of the member.
02-29-2012, 07:56 PM
#7
My engine didn't consume any oil until around 90k miles. One day, a rattling started coming from The lower part of my engine when the engine was revving down around 2krpm. It was the rear pre-cat converter which the inside came lose. When i did my next oil change, I noticed that much less than usual came out... I replaced my rear pre-cat, the rattling dissapeared but the oil consumption is still here at 130k miles...urban legend? I don't think so...
02-29-2012, 07:59 PM
#8
Oh and Markjc, the engine sucking back the gases from the exhaust doesn't only happen at high RPM... Everytime you lift off the gas and use engine brake, the engine pulls a vacuum on the exhaust, whether it's doing 7000rpm or 2000rpm...
02-29-2012, 08:08 PM
#9
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Join Date: Sep 2008
Location: Connecticut
Posts: 836
Haha I found the thread I was thinking of.
http://forums.maxima.org/5th-generat...ront-bank.html
There are some arguments by a member named Erik against the "precat reversion" idea. However A LOT of people disagreed. The people that disagreed have OG status too haha. Child uv Korn, KRRZ350, Scottwax (a little) and even the more recent OG...Rochester (he didn't really take sides but deserves the mention).
BTW, the argument is decent until about post #35 which pretty much won most people. People agree that the precats play a role. They disagree on how much of a role the precats play vs the (possibly poorly designed) piston rings. Back on topic.
Edit: post #48 is a good one too, which Erik never had a response for.
http://forums.maxima.org/5th-generat...ront-bank.html
There are some arguments by a member named Erik against the "precat reversion" idea. However A LOT of people disagreed. The people that disagreed have OG status too haha. Child uv Korn, KRRZ350, Scottwax (a little) and even the more recent OG...Rochester (he didn't really take sides but deserves the mention).
BTW, the argument is decent until about post #35 which pretty much won most people. People agree that the precats play a role. They disagree on how much of a role the precats play vs the (possibly poorly designed) piston rings. Back on topic.
Edit: post #48 is a good one too, which Erik never had a response for.
Last edited by 2damax; 02-29-2012 at 08:16 PM.
02-29-2012, 08:31 PM
#10
Haha I found the thread I was thinking of.
http://forums.maxima.org/5th-generat...ront-bank.html
There are some arguments by a member named Erik against the "precat reversion" idea. However A LOT of people disagreed. The people that disagreed have OG status too haha. Child uv Korn, KRRZ350, Scottwax (a little) and even the more recent OG...Rochester (he didn't really take sides but deserves the mention).
BTW, the argument is decent until about post #35 which pretty much won most people. People agree that the precats play a role. They disagree on how much of a role the precats play vs the (possibly poorly designed) piston rings. Back on topic.
Edit: post #48 is a good one too, which Erik never had a response for.
http://forums.maxima.org/5th-generat...ront-bank.html
There are some arguments by a member named Erik against the "precat reversion" idea. However A LOT of people disagreed. The people that disagreed have OG status too haha. Child uv Korn, KRRZ350, Scottwax (a little) and even the more recent OG...Rochester (he didn't really take sides but deserves the mention).
BTW, the argument is decent until about post #35 which pretty much won most people. People agree that the precats play a role. They disagree on how much of a role the precats play vs the (possibly poorly designed) piston rings. Back on topic.
Edit: post #48 is a good one too, which Erik never had a response for.
Anecdotes and adamant repetition don't qualify as fact in themselves. Case in point? Reference Gizmo's post #7 above with KRRZ350 post you quoted. The front and rear cats are designed entirely different. Erik has a point. There are numerous 'facts' that have been presented on this board, like any media, that have no merit save repetitious claims and the eventual quote of said claims found at a later time in a simple search. Post #48 has no verifiable citation.
IJS...
02-29-2012, 08:36 PM
#11
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Join Date: Sep 2008
Location: Connecticut
Posts: 836
^ Another OG with a great point. I am not NEARLY educated enough in this field to defend any side. I simply chose my side based on who argued better. And you are right about post #48. It is ALL OVER THE WEB but with no citation.
More importantly, lets stay on topic. OP, replace the cat and go from there. I do not see much other options unless you can say more about the noise. You say its horrible. Thats subjective. What is the sound exactly.
More importantly, lets stay on topic. OP, replace the cat and go from there. I do not see much other options unless you can say more about the noise. You say its horrible. Thats subjective. What is the sound exactly.
Last edited by 2damax; 02-29-2012 at 08:59 PM.
02-29-2012, 09:24 PM
#12
Motor ran after it was punched out, but had a knock from low oil (all of it blew out, car burned no oil before).
Nissan had to do a recall on altimas and sentras (iirc) b/c of this. Maxima wasn't included, but should have been.
It can be hit or miss (it's down to driving style apparently, unburnt fuel destroys these). My friend has a 2002 with 170k+ bone stock and it runs strong. But I'm having him get the cats gutted before she blows lol.
Last edited by Child_uv_KoRn; 02-29-2012 at 09:31 PM.
03-01-2012, 09:45 AM
#13
This AGAIN!?
Complete myth, Korn Child. Your pre-cats blew up and clogged your main cat, DOWN. STREAM. and you kept running your car with the exhaust path plugged and forced exhaust to back up into your engine and wreak an untold amount of havoc. Your situation has NOTHING TO DO with the pre-cat-causes-oil-burning theory. Again, how can some of the '02 and '03s start using oil at a whopping 25K miles and your friend made it to 170K without issue? If her rings were bad, they'd already have proven that. If cats destroy rings, why didn't hers get annihilated 8 years ago?
Is it very sad that Nelledge and I seem to be some of the few people willing to think critically about this issue? Yes. Does post count correlate to weight of opinion? Sort of, when it comes to non-scientific things.
Yes, the bandwagon fallacy. I agree that everything read on the internet needs to come sprinkled with salt, but when a theory comes out that completely turns accepted truths on their head, you should be uncapping the shaker to get enough of salt on there!
Did I have a response to KRRZ's image? No. I couldn't find anything from Nissan referencing it.
What confuses me the most is that there is literally years of posts on here discussing the KNOWN PROBLEM with early VQ piston rings causing oil burning and then, out of nowhere, some genius decides that no, it can't POSSIBLY be that easy, logical explanation! It must be pre-cats instead because I want people to buy my headers/buy my aftermarket converters/troll people/whatever! That should account for something. That should raise a huge red flag that, wow, no one was able to figure out why the early VQ35s were burning oil for EIGHT YEARS until some anonymous source decides it's the pre-catalytic converters??
My oil-burning '02 was destroyed. My '05 doesn't burn a drop. Ever. In nearly 10K miles, I can't get it to burn oil. Why? Is it magic changes to the pre-cats? Nope. Different rings, different internals, etc. contribute to a healthier engine with a higher compression ratio and no oil-burning becasue the rings aren't leaking. Heck, get this: my '02 wasn't throwing ANY catalytic converter codes and my '05 is throwing a P0420! If anything, shouldn't everyone with a "nuked precat" and oil-burning have warnings from OBDII stating that the cats aren't working? Shouldn't my 6th gen's low-output cat warning mean I should be sucking massive quanities of substrate into my engine and scarring the cylinder walls so the rings don't fit? Crazy how the facts just don't seem to line up, eh?
Like nelledge said, repeating yourself does NOT bolster your argument, it does not prove a darn thing. So if people refuse to think critically about the problem and just believe what KRRZ says because he opened up one engine and saw some bad rings that one time and immediately conclude that the rings weren't crap from the factory, they were crap from the catalytic converters going BACKWARDS into the engine... Well, I can't help them.
I'm a computer programmer. If I just look at the final result of a program or script I'm debugging, I can't tell why it went wrong, just what went wrong. It's not until I'm leaving myself debug messages and tracing variables that I can determine where the bad logic lies, by watching it fail, by taking repeated measurements. You can NOT open one engine to see the result of a process you haven't seen and throw away EIGHT YEARS of research and opinion and brainshare-time to prove some wacky theory you want to be true.
And, 2damax (clever nick, by the way), you could have mentioned all the questions I raised that the precat disintegration theory can't answer! Huge quotes from me below:
You were completely correct; I was certainly not informed enough to take more of a stand against this "pre-cats cause the VQ35 oil-burning problem" issue, but now that I've asked some technicians at work and done some (gasp!!) reading on the subject, I am ready to take apart your response more carefully. Let's begin.
Correct. Reversion (in the sense you are thinking of) happens at extremely low engine speeds. Extremely low means "idle." Reversion happens at idle. No other time.
Reversion occurs with the pulse of energy from the combustion process, not with the gases themselves. When the pulse hits an area of low-pressure, it bounces off it and travels back towards the exhaust valve, mingling with the exhaust gases along the way. The pulse will change the momentum of some of that gas, but not all of it. Because of that, only trace amounts of exhaust gas can re-enter the combustion chamber.
At high engine speeds, the reversion wave only serves to alter the pressure in the area immediately outside the exhaust valve, helping to suck exhaust gases out more effectively--ie, a tuned exhaust. No gases can enter the chamber because of the major difference in pressures from the intake and exhaust sides of the air system.
Just because your highly abrasive finger can scrape off some pieces of an aged pre-cat doesn't mean that hot gases can do the same thing. Your finger has what, thousands of times more mass than the gas, and exerts a force how much greater than the gas? This isn't a logical "if (my finger)... then (the gas)..." statement.
Impossible. The trace amounts of gas that could reenter the chamber at idle speeds could never carry large enough amounts of the pre-cat (if they really can wear the pre-cat without simply vaporizing its catalyst) into the combustion chamber to cause any change in its environment. Jumping from that statement to a claim that this is damaging the rings beneath the piston head is simply farcical!
No one has ever confirmed this through testing, no one has ever observed this, and no engineer has ever verified that this is even possible. Because of those three rather large facts, you cannot make a statement like "It's what happens, end of story." There is a huge, huge difference between causation
and correlation.
Wikipedia has an entire article on the issue.
Causation: Causes something to happen ("The act or process of causing.")
Correlation: " a relation existing between phenomena or things or between mathematical or statistical variables which tend to vary, be associated, or occur together in a way not expected on the basis of chance alone"
"Correlation does not imply causation" (related to "ignoring a common cause" and questionable cause) is a phrase used in science and statistics to emphasize that correlation between two variables does not automatically imply that one causes the other (though correlation is necessary for linear causation in the absence of any third and countervailing causative variable, and can indicate possible causes or areas for further investigation; in other words, correlation can be a hint)"
The other big problem with this is that the oil-burning issue affects all VQ35s up to a certain, non-specific date. Clearly, the pre-cats in 5.5 gens, 6 gens, 350Zs, Muranos, G35s, and M35s are not all the same.
"Oh, but what if they are all made out of the same material," you say. Well, clearly, if pre-cats could do this, they would be doing it to all sorts of cars from all sorts of manufacturers, not to mention every vehicle Nissan made from 02 - ~05, if not an even greater range of years. The process of taming the harmful pollutants in exhaust gas varies very, very little from manufacturer to manufacturer. There are only so many different catalysts in existence, and only so many ways of securing that catalyst to an apparatus that pulls gas through it to collide the NOx and hydrocarbons with said catalyst.
This is not a closed issue and I still firmly believe that the entire idea of pre-cats causing oil rings to wear is sheerly nonsensical.
Any response you can offer to these points would be greatly appreciated. You yourself don't have to respond, naturally, if there is someone else advocating the idea.
Sources:
http://www.bigcitythunder.com/pages/...ng_exhaust.pdf
http://www.rewarderheaders.com/reversio.htm
http://www.custom-car.us/exhaust/header.aspx
How? Poor assembly from the factory. Could be someone put the wrong set of pistons in the front bank. Could be the front bank cylinders were bored a touch out of spec or not honed properly. I've seen a lot of engines that had issues in just one cylinder that could be traced back to improper assembly, machining or parts selection.
Whatever. I'll let the new users draw their own conclusion, but if you guys seriously think that exhaust carries catalytic converter pieces TOWARDS the engine and that ruined your rings, what other nonsense will you fall for? Be careful, young ones.
Is it very sad that Nelledge and I seem to be some of the few people willing to think critically about this issue? Yes. Does post count correlate to weight of opinion? Sort of, when it comes to non-scientific things.
Originally Posted by Nelledge
There are numerous 'facts' that have been presented on this board, like any media, that have no merit save repetitious claims and the eventual quote of said claims found at a later time in a simple search.
Did I have a response to KRRZ's image? No. I couldn't find anything from Nissan referencing it.
What confuses me the most is that there is literally years of posts on here discussing the KNOWN PROBLEM with early VQ piston rings causing oil burning and then, out of nowhere, some genius decides that no, it can't POSSIBLY be that easy, logical explanation! It must be pre-cats instead because I want people to buy my headers/buy my aftermarket converters/troll people/whatever! That should account for something. That should raise a huge red flag that, wow, no one was able to figure out why the early VQ35s were burning oil for EIGHT YEARS until some anonymous source decides it's the pre-catalytic converters??
My oil-burning '02 was destroyed. My '05 doesn't burn a drop. Ever. In nearly 10K miles, I can't get it to burn oil. Why? Is it magic changes to the pre-cats? Nope. Different rings, different internals, etc. contribute to a healthier engine with a higher compression ratio and no oil-burning becasue the rings aren't leaking. Heck, get this: my '02 wasn't throwing ANY catalytic converter codes and my '05 is throwing a P0420! If anything, shouldn't everyone with a "nuked precat" and oil-burning have warnings from OBDII stating that the cats aren't working? Shouldn't my 6th gen's low-output cat warning mean I should be sucking massive quanities of substrate into my engine and scarring the cylinder walls so the rings don't fit? Crazy how the facts just don't seem to line up, eh?
Like nelledge said, repeating yourself does NOT bolster your argument, it does not prove a darn thing. So if people refuse to think critically about the problem and just believe what KRRZ says because he opened up one engine and saw some bad rings that one time and immediately conclude that the rings weren't crap from the factory, they were crap from the catalytic converters going BACKWARDS into the engine... Well, I can't help them.
I'm a computer programmer. If I just look at the final result of a program or script I'm debugging, I can't tell why it went wrong, just what went wrong. It's not until I'm leaving myself debug messages and tracing variables that I can determine where the bad logic lies, by watching it fail, by taking repeated measurements. You can NOT open one engine to see the result of a process you haven't seen and throw away EIGHT YEARS of research and opinion and brainshare-time to prove some wacky theory you want to be true.
And, 2damax (clever nick, by the way), you could have mentioned all the questions I raised that the precat disintegration theory can't answer! Huge quotes from me below:
Originally Posted by My initial post, relying on ACTUAL CITATIONS and LOGIC
Originally Posted by KRRZ350
I'll gladly explain it, since it's bloody obvious you aren't informed here.
Reversion, in a nutshell your engine will occasionally suck exhaust gasses back into the motor.
Reversion occurs with the pulse of energy from the combustion process, not with the gases themselves. When the pulse hits an area of low-pressure, it bounces off it and travels back towards the exhaust valve, mingling with the exhaust gases along the way. The pulse will change the momentum of some of that gas, but not all of it. Because of that, only trace amounts of exhaust gas can re-enter the combustion chamber.
At high engine speeds, the reversion wave only serves to alter the pressure in the area immediately outside the exhaust valve, helping to suck exhaust gases out more effectively--ie, a tuned exhaust. No gases can enter the chamber because of the major difference in pressures from the intake and exhaust sides of the air system.
The front pre-cat doesn't get clogged, it is made of a substrate that is way to brittle, you literally touch it and it crumbles to sandy little bits on your finger, yes merely from touching it.
Well between that, and the process of reversion, some of that substrate makes its way back into the motor & wears the rings
It's what happens, end of story. Whether the rings are crap or not definitly helps, but I guarantee you those cars with 20K that are burning oil have missing pieces from the front cat.
and correlation.
Wikipedia has an entire article on the issue.
Causation: Causes something to happen ("The act or process of causing.")
Correlation: " a relation existing between phenomena or things or between mathematical or statistical variables which tend to vary, be associated, or occur together in a way not expected on the basis of chance alone"
"Correlation does not imply causation" (related to "ignoring a common cause" and questionable cause) is a phrase used in science and statistics to emphasize that correlation between two variables does not automatically imply that one causes the other (though correlation is necessary for linear causation in the absence of any third and countervailing causative variable, and can indicate possible causes or areas for further investigation; in other words, correlation can be a hint)"
The other big problem with this is that the oil-burning issue affects all VQ35s up to a certain, non-specific date. Clearly, the pre-cats in 5.5 gens, 6 gens, 350Zs, Muranos, G35s, and M35s are not all the same.
"Oh, but what if they are all made out of the same material," you say. Well, clearly, if pre-cats could do this, they would be doing it to all sorts of cars from all sorts of manufacturers, not to mention every vehicle Nissan made from 02 - ~05, if not an even greater range of years. The process of taming the harmful pollutants in exhaust gas varies very, very little from manufacturer to manufacturer. There are only so many different catalysts in existence, and only so many ways of securing that catalyst to an apparatus that pulls gas through it to collide the NOx and hydrocarbons with said catalyst.
This is not a closed issue and I still firmly believe that the entire idea of pre-cats causing oil rings to wear is sheerly nonsensical.
Any response you can offer to these points would be greatly appreciated. You yourself don't have to respond, naturally, if there is someone else advocating the idea.
Sources:
http://www.bigcitythunder.com/pages/...ng_exhaust.pdf
http://www.rewarderheaders.com/reversio.htm
http://www.custom-car.us/exhaust/header.aspx
Originally Posted by Me
KRRZ, you just don't get it, but that's whatever. Keep spreading misinformation! It's the internet, after all. Don't sweat all my questions you were unable to answer because your pet theory can't explain them. Just keep doin' your thing.
@Crusher: How large would the piece of metal have to be? Are we talking measurements on the scale of millimeters or micrometers? I'm not seeing how chunks of any considerable size could move back into the engine. Surely pieces of metal that measure .01 mm across would just incinerate before doing any damage. KKZ didn't mention scarring on the cylinder walls and I can't make much out of his pictures. Doesn't scoring happen from a ton of different reasons, though? How would you be able to determine it was the pre-cat? It leads to a chicken-and-egg thing: Did the pre-cat hurt the rings that led to low-oil conditions that caused scoring, or did low-oil conditions cause scoring that gets blamed on the pre-cat?
I don't remember people on here mentioning Nissan gave them new exhaust manifolds/pre-cats with the new engine. I assumed Nissan would replace the bare minimum, but you're saying that included new pre-cats?
@Scottwax: That's what I thought, until further research revealed the ludicrously tiny odds of a pre-cat being able to damage the oil rings.
Here's an interesting post I dug up on an MR2 Spyder forum:
Is the VVT in our engines aggressive enough to allow pre-cats to enter the engine? I don't think so--we don't drive sports cars. Also, those guys were saying they'd pulled pre-cats at 15K miles and they were heavily damaged, implying that you can't expect your engine to live past 60K miles without removing the pre-cats..! Obviously, our situation isn't the same.
@Crusher: How large would the piece of metal have to be? Are we talking measurements on the scale of millimeters or micrometers? I'm not seeing how chunks of any considerable size could move back into the engine. Surely pieces of metal that measure .01 mm across would just incinerate before doing any damage. KKZ didn't mention scarring on the cylinder walls and I can't make much out of his pictures. Doesn't scoring happen from a ton of different reasons, though? How would you be able to determine it was the pre-cat? It leads to a chicken-and-egg thing: Did the pre-cat hurt the rings that led to low-oil conditions that caused scoring, or did low-oil conditions cause scoring that gets blamed on the pre-cat?
I don't remember people on here mentioning Nissan gave them new exhaust manifolds/pre-cats with the new engine. I assumed Nissan would replace the bare minimum, but you're saying that included new pre-cats?
@Scottwax: That's what I thought, until further research revealed the ludicrously tiny odds of a pre-cat being able to damage the oil rings.
Here's an interesting post I dug up on an MR2 Spyder forum:
Woah, wait a minute! How can the pre-cat get back into the engine: Surely the exhaust flow pushes it all out?
True to a certain extent, but here's the clever bit…
The 1ZZ-FE engine (Toyota's designation for the engine inside the MR2 Roadster) is a very clever piece of kit, and arguably its main party piece is the VVTi, or Variable Valve Timing Intelligent. This increases engine response all over the rev range by altering the timing of the cams, allowing for differing amounts of valve overlap in order to give great low-down torque as well as good top-end power. The 1ZZ also uses it's VVT to perform EGR (Exhaust Gas Recirculation) functions without the aid of a specific valve like other cars. Under certain operating conditions (usually steady cruise) the cams are timed to scavenge some exhaust gas back into the cylinders, as a way of reducing the high hydrocarbon emissions that modern petrol engines generate at certain times.
Unfortunately, when you combine this with some very sharp ceramic pre-cat particles, you can imagine what happens: The pre-cats start breaking down, and get dropped into the main cat which then causes excessive pressure, leading to oil blow-by in the engine. When the VVTi kicks in, the pre-cats are sucked back in and scratch and score the cylinder walls, leading to more oil passing by the piston rings and being burnt off without you even realising it. No oil in an engine leads to massive failure as every moving part grinds against metal, and in short you end up with a practically useless engine. When this happens the situation is compounded by the fact that hot oil is now allowed to drip directly onto the pre-cats and break them down even quicker, which in turn allows large chunks to block the main cat even more, which then stops any smaller pre-cat material escaping at all and sucks even more back into the engine to cause even more damage… A vicious circle of the very worst kind.
Some common symptoms of pre-cat failure are extreme oil loss, very noticeable lack of power all the way through the rev range, and horrible noises coming from your engine bay. Essentially, if you've got any of these problems and they are directly related to pre-cat loss, then it's too late. Even the oil warning light won't save you here, as by the time it comes on there's almost zero oil left in the engine anyway.
But I've read elsewhere that the pre-cats themselves are fine, it the piston rings which are the weakness…
This is where we come across a real conundrum, and a question to which no-one has a definitive answer. It's true that on very early MK3s there was a known problem with the piston rings themselves on a 1ZZ, and Toyota issued a technical document to the dealers around the world stating as such. They also changed the design of the piston rings for the facelift version of the Roadster, which became available in 2003.
Now whether it's a case of the piston rings failing, oil dripping onto the pre-cats and breaking them up, or the pre-cats self destructing and taking the piston rings with them, we just don't know. All we do know for certain is that whilst you can't take the piston rings out of the engine, you can remove the pre-cats from the manifold. No pre-cats = Nothing to get sucked back into the engine.
True to a certain extent, but here's the clever bit…
The 1ZZ-FE engine (Toyota's designation for the engine inside the MR2 Roadster) is a very clever piece of kit, and arguably its main party piece is the VVTi, or Variable Valve Timing Intelligent. This increases engine response all over the rev range by altering the timing of the cams, allowing for differing amounts of valve overlap in order to give great low-down torque as well as good top-end power. The 1ZZ also uses it's VVT to perform EGR (Exhaust Gas Recirculation) functions without the aid of a specific valve like other cars. Under certain operating conditions (usually steady cruise) the cams are timed to scavenge some exhaust gas back into the cylinders, as a way of reducing the high hydrocarbon emissions that modern petrol engines generate at certain times.
Unfortunately, when you combine this with some very sharp ceramic pre-cat particles, you can imagine what happens: The pre-cats start breaking down, and get dropped into the main cat which then causes excessive pressure, leading to oil blow-by in the engine. When the VVTi kicks in, the pre-cats are sucked back in and scratch and score the cylinder walls, leading to more oil passing by the piston rings and being burnt off without you even realising it. No oil in an engine leads to massive failure as every moving part grinds against metal, and in short you end up with a practically useless engine. When this happens the situation is compounded by the fact that hot oil is now allowed to drip directly onto the pre-cats and break them down even quicker, which in turn allows large chunks to block the main cat even more, which then stops any smaller pre-cat material escaping at all and sucks even more back into the engine to cause even more damage… A vicious circle of the very worst kind.
Some common symptoms of pre-cat failure are extreme oil loss, very noticeable lack of power all the way through the rev range, and horrible noises coming from your engine bay. Essentially, if you've got any of these problems and they are directly related to pre-cat loss, then it's too late. Even the oil warning light won't save you here, as by the time it comes on there's almost zero oil left in the engine anyway.
But I've read elsewhere that the pre-cats themselves are fine, it the piston rings which are the weakness…
This is where we come across a real conundrum, and a question to which no-one has a definitive answer. It's true that on very early MK3s there was a known problem with the piston rings themselves on a 1ZZ, and Toyota issued a technical document to the dealers around the world stating as such. They also changed the design of the piston rings for the facelift version of the Roadster, which became available in 2003.
Now whether it's a case of the piston rings failing, oil dripping onto the pre-cats and breaking them up, or the pre-cats self destructing and taking the piston rings with them, we just don't know. All we do know for certain is that whilst you can't take the piston rings out of the engine, you can remove the pre-cats from the manifold. No pre-cats = Nothing to get sucked back into the engine.
Originally Posted by Not you
Again, if this was as simple as one easy-to-replace component being the culprit, why was Nissan replacing entire engines instead of just swapping out the pre-cats? Hmm, probably because they have nothing to do with the oil-consumption problem.
Why did the oil-burning problem go away sometime during the 6th generation of Maximas? Did they start using a different kind of pre-cat, or did they make an internal change in the rings after the oil-burning problem was known? Hmm... I'm only seeing one set of catalysts listed for the 6th gens on Courtesy's website...
The compression ratio on the 3.0 block is roughly 10.0:1, the compression ratio on ours is either 10.3 or 10.5:1, depending on your source. Nissan bored out the block and called it a day, not upgrading their piston oil rings until it became obvious that they were deteriorating in real-world conditions under the additional stress of the higher compression ratio.
This has already been talked to death, we all know its the rings, so why is it so hard to just admit that Nissan used crappy, crappy rings? Maybe it wasn't Nissan's fault, per se, maybe the supplier screwed up a few hundred thousand and those took a few years to use up. The details are uncertain, but it's obvious that the pre-cats have nothing to do with the bad rings. The "logic" connecting the pre-cats to the bad rings is flimsy at best and "insult my intelligence" wrong at worst.
Are you seriously telling me that the pre-cats on Maximas, G35s, 350Zs, Muranos, M35s, and FX35s WERE ALL THE SAME!? All made out of exactly the same materials, all made with the exact same bends and whatever else is needed to ensure that they all break exactly the same way? A far, far more logical explanation, ONE WE ALREADY KNOW, is that bad rings were shared between the engines in FWD and RWD VQ35 blocks.
Ice cream sales and drowning deaths, people. SPURIOUS RELATIONSHIPS: http://en.wikipedia.org/wiki/Correla...s_both_A_and_B
@[KRRZ]: Yeah, because taking an engine apart means you know what caused the damage. Wrong! Taking an engine apart can certainly reveal the cause of damage in some scenarios (a hole in a cylinder wall, bad valves, etc), but there are also many other variables at play that can't be known by looking at a broken engine laying in pieces on your workbench. Why were only some of the rings in that engine bad? I don't know. Why don't all VQ35s burn oil?
Why did the oil-burning problem go away sometime during the 6th generation of Maximas? Did they start using a different kind of pre-cat, or did they make an internal change in the rings after the oil-burning problem was known? Hmm... I'm only seeing one set of catalysts listed for the 6th gens on Courtesy's website...
The compression ratio on the 3.0 block is roughly 10.0:1, the compression ratio on ours is either 10.3 or 10.5:1, depending on your source. Nissan bored out the block and called it a day, not upgrading their piston oil rings until it became obvious that they were deteriorating in real-world conditions under the additional stress of the higher compression ratio.
This has already been talked to death, we all know its the rings, so why is it so hard to just admit that Nissan used crappy, crappy rings? Maybe it wasn't Nissan's fault, per se, maybe the supplier screwed up a few hundred thousand and those took a few years to use up. The details are uncertain, but it's obvious that the pre-cats have nothing to do with the bad rings. The "logic" connecting the pre-cats to the bad rings is flimsy at best and "insult my intelligence" wrong at worst.
Are you seriously telling me that the pre-cats on Maximas, G35s, 350Zs, Muranos, M35s, and FX35s WERE ALL THE SAME!? All made out of exactly the same materials, all made with the exact same bends and whatever else is needed to ensure that they all break exactly the same way? A far, far more logical explanation, ONE WE ALREADY KNOW, is that bad rings were shared between the engines in FWD and RWD VQ35 blocks.
Ice cream sales and drowning deaths, people. SPURIOUS RELATIONSHIPS: http://en.wikipedia.org/wiki/Correla...s_both_A_and_B
@[KRRZ]: Yeah, because taking an engine apart means you know what caused the damage. Wrong! Taking an engine apart can certainly reveal the cause of damage in some scenarios (a hole in a cylinder wall, bad valves, etc), but there are also many other variables at play that can't be known by looking at a broken engine laying in pieces on your workbench. Why were only some of the rings in that engine bad? I don't know. Why don't all VQ35s burn oil?
Originally Posted by SCOTTWAX
Originally Posted by KRRZ350
So again, can you please explain why on this motor I have 6 rings on the front cylinders worn way beyond spec but 6 rings on the back all within spec?
I'll agree that the rings have problems on 3.5's, and that there are plenty out there that burn oil without pre-cat issues, but THIS car is a clear cut case of the precats grinded up the rings on the front bank.
FYI, the rev-up motor that had 15K on it when I drill/ball honed & reringed with '02 maxima rings 2+ years ago now has 75k on it and has been boosted for the last 10K. 1/4-1/2 qt low between oil changes. Something to think about.
I'll agree that the rings have problems on 3.5's, and that there are plenty out there that burn oil without pre-cat issues, but THIS car is a clear cut case of the precats grinded up the rings on the front bank.
FYI, the rev-up motor that had 15K on it when I drill/ball honed & reringed with '02 maxima rings 2+ years ago now has 75k on it and has been boosted for the last 10K. 1/4-1/2 qt low between oil changes. Something to think about.
Originally Posted by Eirik
I tried looking into this situation more on my lunch break today, but was (gasp!) basically unable to link valve overlap to pre-cat failure. In fact, the only posts I was digging up were either about the Nissan Sentra recall thing, or that MR2 forum.
Kinda crazy how this issue is so hard to research, given that it must happen to tens of thousands of cars from every manufacturer.
@Scott: EXACTLY! Everything about this whole oil-burning matter suggests human sloppiness! Why doesn't every car burn oil? Obviously, not all of the VQ35s from '02-'0X were improperly assembled/had bad rings installed/whatever. If this was a hardcore, the pre-cats melt j00r enjunz PERIOD LOL sort of deal, you'd see it on 90%+ of the VQ35s, right? We're only seeing between 25-40%.
Kinda crazy how this issue is so hard to research, given that it must happen to tens of thousands of cars from every manufacturer.
@Scott: EXACTLY! Everything about this whole oil-burning matter suggests human sloppiness! Why doesn't every car burn oil? Obviously, not all of the VQ35s from '02-'0X were improperly assembled/had bad rings installed/whatever. If this was a hardcore, the pre-cats melt j00r enjunz PERIOD LOL sort of deal, you'd see it on 90%+ of the VQ35s, right? We're only seeing between 25-40%.
Last edited by Eirik; 03-01-2012 at 09:53 AM.
03-01-2012, 10:32 AM
#14
Senior Member
Join Date: Sep 2008
Location: Connecticut
Posts: 836
There was a lot I did not say in that post. For one, you should have been under that OG list. Two, I did not list your points. My car has original precats and burns over 1.5 qts every 1k. Who knows the original cause. If I had headers at 5k miles would this have been as severe? Who knows?
I did not want this to get so off topic. That happens to often with all these new guys as is. I tried to keep it short. Why did I even speak!! Haha.
Btw, I read your post in another thread and the answer is yes. The 15 post minimum is no more. Did you get like an e-mail when I mentioned your name. I have not seen you or Child in a while and then one mention is like the bat signal. Wheres scottwax lol.
I did not want this to get so off topic. That happens to often with all these new guys as is. I tried to keep it short. Why did I even speak!! Haha.
Btw, I read your post in another thread and the answer is yes. The 15 post minimum is no more. Did you get like an e-mail when I mentioned your name. I have not seen you or Child in a while and then one mention is like the bat signal. Wheres scottwax lol.
03-01-2012, 10:44 AM
#15
Newbie - Just Registered
Join Date: Jan 2009
Posts: 12
A couple years ago I replaced all three after milking for as long as I could with direct fit from Eastern Catalytic sold through distributor. IMHO they all go eventually. Eastern are good people and stand by their products. I suggest disconnecting the cats and making sure the motor is good before moving further.
03-01-2012, 11:00 AM
#16
Back to OP's original point.
You have to pull the cat and physically check it. If you had a P0420 code then pull the y-pipe (rear pre-cat) for that bank first. If it looks OK, then you'll have to pull the other pre-cat to check it.
I think you just need to replace one or two of your cats, or punch them out. Make sure to check your main cat as well since any breaking up of the pre-cat will eventually make it down to the main cat and start clogging it.
You have to pull the cat and physically check it. If you had a P0420 code then pull the y-pipe (rear pre-cat) for that bank first. If it looks OK, then you'll have to pull the other pre-cat to check it.
I think you just need to replace one or two of your cats, or punch them out. Make sure to check your main cat as well since any breaking up of the pre-cat will eventually make it down to the main cat and start clogging it.
03-01-2012, 11:16 AM
#17
The biggest issue I noticed when my precats were going bad is lack of power. When I replaced the precats, I also replaced the main cat with a test pipe. My 45-85 time dropped by close to 3 seconds. Oil consumption never changed from the time I bought the car with 113k miles on it other than a little worsening when the valve covers started leaking. Still running strong at 195k miles when a drunk totaled it.
My current car, an '04 V6 Accord has precats close to the engine like in the Maxima and I'm going 9-10k miles between oil changes with synthetic oil and have zero oil loss in between changes. Can't imagine that the precat suppliers to Nissan and Honda are so far apart in quality of their products. BTW, they make PCD's (pre-cat deletes) for the J30 that includes O2 extenders so you don't get an SES light. Too bad with the Maxima the options are only headers or gutting the pre-cats.
My current car, an '04 V6 Accord has precats close to the engine like in the Maxima and I'm going 9-10k miles between oil changes with synthetic oil and have zero oil loss in between changes. Can't imagine that the precat suppliers to Nissan and Honda are so far apart in quality of their products. BTW, they make PCD's (pre-cat deletes) for the J30 that includes O2 extenders so you don't get an SES light. Too bad with the Maxima the options are only headers or gutting the pre-cats.
03-01-2012, 02:18 PM
#18
Member
Thread Starter
Join Date: Oct 2009
Location: Charlotte,NC
Posts: 174
re
Ok. This thing got huge. I applaud everyones replies, and def your thought, and time. You guys are great, and i am appreciative of your comments.
Right now, i havent driven the car in a week. The difference in driving the car was the noise, power loss and MPG drop.
I am getting the cats gutted today. But, i think i should be ok. The code after i reset it went away.
Car isnt burning oil though, its leaking it through the oil cooler, which i just found out.
What will make you think engine would die, just not start anymore ? struggle way too much or what
Right now, i havent driven the car in a week. The difference in driving the car was the noise, power loss and MPG drop.
I am getting the cats gutted today. But, i think i should be ok. The code after i reset it went away.
Car isnt burning oil though, its leaking it through the oil cooler, which i just found out.
What will make you think engine would die, just not start anymore ? struggle way too much or what
03-01-2012, 02:39 PM
#19
Member
Thread Starter
Join Date: Oct 2009
Location: Charlotte,NC
Posts: 174
Ok. This thing got huge. I applaud everyones replies, and def your thought, and time. You guys are great, and i am appreciative of your comments.
Right now, i havent driven the car in a week. The difference in driving the car was the noise, power loss and MPG drop.
I am getting the cats gutted today. But, i think i should be ok. The code after i reset it went away.
Car isnt burning oil though, its leaking it through the oil cooler, which i just found out.
What will make you think engine would die, just not start anymore ? struggle way too much or what
Right now, i havent driven the car in a week. The difference in driving the car was the noise, power loss and MPG drop.
I am getting the cats gutted today. But, i think i should be ok. The code after i reset it went away.
Car isnt burning oil though, its leaking it through the oil cooler, which i just found out.
What will make you think engine would die, just not start anymore ? struggle way too much or what
I doubt it. no CEL and oil and all fluids are at good levels.
03-01-2012, 05:00 PM
#20
Junior Member
Join Date: Dec 2011
Location: New Jersey
Posts: 27
Ah you're right.. I forgot about the vacuum the piston draws off-throttle. Thanks for the correction.
03-01-2012, 11:06 PM
#21
Piston rings don't go bad within 1000 miles (by themselves so bad as to kill the engine), you moron, on fresh synthetic. Get a Fing clue.
My friend's maxi is fine b/c the precats are still in good shape (DUH).
My precats had disintegrated but didn't cause a loss of power till the very end when the main cat clogged, which was instantaneous, there was no gradual decline in power. They didn't rattle around, so how would I know it was grinding the **** out of cylinder walls? I couldn't have been driving around with severe back pressure blowing oil out and forcing the material in the cylinders....which you say doesn't happen, but just admitted to it.
Are you saying nissan replaced all of those engines for no reason? STFU and GTFO. Two different problems with two different consequences resulting in oil burning.
Everything you posted just reinforces it. I imagine lighting and thunder are just coincidences for you.
/donewithtisthread
My friend's maxi is fine b/c the precats are still in good shape (DUH).
My precats had disintegrated but didn't cause a loss of power till the very end when the main cat clogged, which was instantaneous, there was no gradual decline in power. They didn't rattle around, so how would I know it was grinding the **** out of cylinder walls? I couldn't have been driving around with severe back pressure blowing oil out and forcing the material in the cylinders....which you say doesn't happen, but just admitted to it.
Are you saying nissan replaced all of those engines for no reason? STFU and GTFO. Two different problems with two different consequences resulting in oil burning.
Everything you posted just reinforces it. I imagine lighting and thunder are just coincidences for you.
/donewithtisthread
Last edited by Child_uv_KoRn; 03-01-2012 at 11:41 PM.
03-02-2012, 06:24 AM
#22
Senior Member
Join Date: Sep 2008
Location: Connecticut
Posts: 836
Man, I am really sorry because I feel I started this. This thread is not about proving precats cause oil burning.
Also, a debate in another thread is fine but once someone throws out insults it shows they are to close minded to truly respect and listen to opposing points. Good rhetoric will win debates, not insults.
Also, a debate in another thread is fine but once someone throws out insults it shows they are to close minded to truly respect and listen to opposing points. Good rhetoric will win debates, not insults.
03-02-2012, 02:46 PM
#23
2damax: I'm certainly not an OG. Unless "OG" now means "Someone who registered more than six months ago." I just happened to see this post in my first visit in quite some time, ha.
KORN CHILD: Whatever, brospeh.
@OP: It's expensive to fix an engine's low compression. =/ Have you had a vacuum and leak-down test performed to get some solid numbers on what might be out-of-spec? I can tell you, the switch from my leaky 5.5 gen VQ35 to my solid 6th gen VQ35 was massive. Even though the newer car is massive (way, way too big) and heavy, it feels like it's got double the guns of my first Maxima! The first one made wonderful noises, but you didn't really feel like it was accelerating to match the glorious sounds. My 6th gen is way too quiet, but it'll yank you up to speed in a hurry. Who knows how many horses escaped around the bad rings on my first car... 15? 30? Enough to be noticeable. The crappy part for you, though, is you know how your car felt when it was fresher and a taut, driving machine. I picked mine up with oil-burning, so I have no idea how much more crazy-awesome it would have been in its heyday.
KORN CHILD: Whatever, brospeh.
@OP: It's expensive to fix an engine's low compression. =/ Have you had a vacuum and leak-down test performed to get some solid numbers on what might be out-of-spec? I can tell you, the switch from my leaky 5.5 gen VQ35 to my solid 6th gen VQ35 was massive. Even though the newer car is massive (way, way too big) and heavy, it feels like it's got double the guns of my first Maxima! The first one made wonderful noises, but you didn't really feel like it was accelerating to match the glorious sounds. My 6th gen is way too quiet, but it'll yank you up to speed in a hurry. Who knows how many horses escaped around the bad rings on my first car... 15? 30? Enough to be noticeable. The crappy part for you, though, is you know how your car felt when it was fresher and a taut, driving machine. I picked mine up with oil-burning, so I have no idea how much more crazy-awesome it would have been in its heyday.
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