Misfire under load in swapped 3.5

whlimi · 06-10-2008, 11:07 AM

The car was misfiring in the 1700-2200 rpm range sometimes higher for quite a while. It never gave me any misfire codes until last night when I got P0302 for the first time (Cyl. #2 misfire) Anyway, I start it up this morning and the code is gone. I took it for a drive and the same symptoms were there. It starts hesitating and hiccuping in the mentioned range. I tested the resistance on all of the front coils and they're all the same. I tried pulling the coil with the engine running and it made a slight difference which was the same as the other 2 coils. I used a stethoscope on the injectors and all are clicking. I also swapped the coil from #2 to #4 to see if I get a cyl. 4 misfire. (I'll have to wait a while to see if this happens) The plugs look normal not grimy or anything. I know a misfire under load is usually a bad coil but is there anything else I can check before having to purchase coils. And is it normal for the misfire code to disappear on it's own without being erased? Mods are in signature.

Thanks.

whlimi · 06-10-2008, 08:59 PM

Switched coils between #4 and #2 and still got P0302. So it's not the coil. Although the injector is clicking I'm going to see if it's actually delivering fuel. Another thing I found is that the misfire is directly connected with throttle position. I can make it misfire on purpose just by opening the throttle a certain amount regardless of RPM. The car feels like it has less power than when I had the 3.0. Any help is appreciated.

*oldngivout* · 06-11-2008, 01:01 PM

I had a bad #4 injector on a 3.0 VQ recently. A stethoscope told me that it was firing, but the coil pack swap & spark plug swap yielded no results. So I changed the injector and the problem disappeared. But you're right, do the simple things first, then move on.

whlimi · 06-11-2008, 09:32 PM

The thing that's bothering me is that it is not giving me any misfire codes any more but it's still sputtering and jerking like crazy when I give it some gas. It has no where near as much power as it did before. I put in new plugs today and it misfired again and I was eager to pull the code but there was nothing. I'm leaning towards an injector issue. This has been a very frustrating week. I dont want to start buying parts and then realize the issue was something else.
Has anyone else experienced an injector that clicked but was not delivering fuel?
Is there any other way of checking for fuel delivery other than removing the fuel rail and visually checking while cranking? And if it is the injector, why is it that I only feel the bucking and hesitation under medium to heavy throttle? Under light throttle it doesnt even feel like it's missing. But if I go to pass someone it feels like i'm missing a cylinder.

*oldngivout* · 06-11-2008, 10:30 PM

Quote:

Originally Posted by whlimi

And if it is the injector, why is it that I only feel the bucking and hesitation under medium to heavy throttle? Under light throttle it doesnt even feel like it's missing. But if I go to pass someone it feels like i'm missing a cylinder.

That's because the engine requires the most fuel delivery during heavy acceleration. I highly suspect that your bad injector is causing this problem. I have seen it several times before; the engine runs almost perfectly under light load or cruising. But when you try to accelerate, the miss in that cylinder is more noticeable.

Heck, just be glad it's #2, one of the easy ones in front.

**nismology** · 06-11-2008, 11:14 PM

Just a tidbit of info....

Injectors very rarely "go bad". They are just clogged so badly that the spray pattern has gone to hell or is nonexistant. As long as it clicks it's good. They just need some lovin' is all.

whlimi · 06-11-2008, 11:35 PM

Quote:

Originally Posted by nismology

Just a tidbit of info....

Injectors very rarely "go bad". They are just clogged so badly that the spray pattern has gone to hell or is nonexistant. As long as it clicks it's good. They just need some lovin' is all.

I will use some fuel injector cleaner tomorrow and see if that helps. I'm hoping it's the injector because if it's not then I'm probably looking at bigger problems since coil pack and spark plug were ruled out. Another thing that's puzzled me is that why is the ECU not throwing a code when the car is misfiring so horribly. No codes after I erased the last ones 2 nights ago.

**nismology** · 06-12-2008, 10:13 AM

Techron fuel injector cleaner or nothing if it has to be off-the-shelf, IMO.

*cw96* · 06-12-2008, 03:43 PM

Had this is same problem and it drove me nuts for a while. Misfire #2 cylinder code also got a multiple cylinder misfire code. Turns out the connector to the #2 injector was loose and not making a good connection. Sounds like a bad injector or loose wires. Good luck

black_maxed95 · 06-12-2008, 03:54 PM

Quote:

Originally Posted by nismology

Techron fuel injector cleaner or nothing if it has to be off-the-shelf, IMO.

what do you recommend for 'not off the shelf'?
Im having this exact same problem except im occasionally throwing a different code, 0905 for the CKPS POS sensor but its not that.

Also to the OP, do you have hard starts too?

whlimi · 06-12-2008, 10:46 PM

Car starts up fine. It's annoying because it's not throwing codes anymore and I want to know if it's still #2 causing all the misfire. It's weird because now it only randomly misfires and is not as bad as before but I havent really done anything. The power loss is the most noticeable thing because it's there even when the car isnt misfiring. Today I added some fuel injector cleaner and drove for about 60 miles and nothing has changed.

Here's a thought. During a misfire, if the ECU detects that damage can be done to the catalytic converter, the SES light starts blinking and a code is stored. The cat will only be damaged if there's fuel and no spark right...? In my situation, I have a misfire but no codes or blinking SES. From this can I come to the conclusion that I have intermittent fuel loss or complete fuel cut from the #2 injector? Can this happen to an injector where it would spray fine one second and then jam up the next?

*oldngivout* · 06-13-2008, 07:13 AM

Yes, intermittent failure of engine components is common, and very frustrating to diagnose. So you have swapped a known good coil pack & spark plug with no results? So maybe it is time to try an injector. They can and DO fail, sometimes all at once, or perhaps like yours.

Sure it's a pain to do, but all this surmising isn't going to fix anything. Sometimes all you can do is swap parts until you fix it, especially when the offending part is difficult to test or repair.

whlimi · 06-13-2008, 08:16 PM

Today I took off the IM and replaced the rear plugs and inspected the injectors. Rear injectors were clicking. One of the wires for #3 was in pretty rough shape so I soldered it up. I fired the car up and right away I could tell it was running great. I took it for a drive and tried everything but couldnt get it to misfire. It might have been that wire on cylinder 3 injector or the rear plugs. Who knows....I'm just glad its running good again...why it gave me a cylinder 2 misfire code I'll never know but I'm not going to lose sleep over it. The lesson I learned is that I shouldnt have spent all my time on cylinder 2. I should have explored all cylinders.

Thanks all for your input and helping me through this!