surban1

iTrader: (17)

thanks in advance to any helpful input from everyone. i've already searched and was hoping for a "eureka" insight before I start taking stuff apart.

I've been getting code P0450 intermittently (I get it a few times and the cel goes on, I reset it and then don't get it for a while & then i'll get it again). it may be more likely to give error code after fuel tank has been filled up (code just happened again after filling up and had not had it for several weeks while tank was between a 1/4 and 3/4 full) to a full tank (not overfilled but just filled completely up). when I take off the gas cap, I hear hissing so the fuel tank (and the whole evap system maybe?) is pressurized...so, does this mean that the evap canister vent control valve (the valve that attaches to the charcoal tank and that everyone sprays with wd40) is OK and not the cause of the p0450? for if the evap canister vent control valve were stuck open (a potential cause of p0450) the fuel tank wouldn't have any pressure in it. am I right in my thinking about that? i'm not sure so I was hoping for someone with experience to share some of their firsthand knowhow. i'm hoping that the fact that the fuel tank pressurizes will help narrow down the potential causes of this code and i'm trying to eliminate potential issues so that I can try and troubleshoot this code as good as possible.

thanks again for any help and i'll keep my eye on the full tank fill up & code being triggered potential relationship & keep everyone informed.

surban1

iTrader: (17)

just came back in from trying to test the harness with a multi-meter and ran into some issues. there's a lot of rust on everything around down there and having a tough time finding something to use as a ground (couldn't even get continuity on any piece of metal back there if probes were more than 1/4" apart on any piece near to the sensor & its harness).
the fsm says to look for 5 volts between terminal 3 and ground and then continuity between terminal 1 and ground...can I just check for 5 volts between terminal 3 and terminal 1 and that would tell me that those two terminals on the harness are OK?
also had a tough time getting the probe tips into the pin slots on the harness so will need to figure out something on that also. thanks for any advice or tips.

DennisMik

iTrader: (2)

Personally, I would check the EVAP Canister Vent Control Valve before you put more time into this. Those vent control valves love to corrode and not work.

For a ground, open the rear door and use the striker bar that the door latches onto.

For probing into connectors, meter leads are useless. You need something much smaller. I use the straight pins that you get when you buy a long sleeve dress shirt. I use a shot wire with what is called ball clips on the ends between the straight pin and the meter lead.

surban1

iTrader: (17)

thanks for the input. along the lines that you're thinking and hoping that it would be something easy, I took off & checked the evap canister vent control valve earlier today and it tested fine (opened and closed freely with 12v applied and sealed fine; its harness is also fine). I noticed that after car is warmed up and been driven around a bit, that when in park and at idle (so its at closed throttle) that there is suction through the fresh air tube leading into the canister. when I first start up, there is no suction through this tube. from the fsm, it seems that there should NOT be suction through the canister at idle (ie closed throttle). does this help diagnose anything???

I need to get some longer leads for my multimeter and do the pin thing you suggested but when I took off the connecter for the evap control system pressure sensor, I got a code p0446 (the canister vent valve) and when I reconnected the pressure sensor and then disconnected the canister vent valve I got code p1441 (vacuum cut valve bypass valve). so I don't know! I hate evap issues!!!!!

since when the evap pressure sensor was disconnected, I got the p0446, i'm thinking that the pressure sensor is ok and since i'm getting suction through the canister at idle (when I don't think i'm supposed to) i'm thinking that the evap canister purge control valve solenoid and/or the evap canister purge control valve (both under the hood) could be the culprit(s).

all I can add is that i recently switched the map/baro sensor (aka the "boost" sensor) and the map/baro switch (I was getting a p1105) and maybe the "boost" sensor is giving an odd reading and the ecm is getting pissed off about it ;(.
i'm hoping that the sucking through the canister (when I don't believe it should be) will be the clue someone here needs to know what's wrong with my max. hopefully some super troubleshooter (or someone who suffered with the same woes previously) will have an insight. thanks again and i'll post more after I do some more testing.

surban1

iTrader: (17)

I switched the map/baro sensor (aka the "boost" sensor) this morning and still got the p0450 code and suction through the canister just as a fyi, when I checked the canister vent valve harness connector I just checked that it was getting battery voltage (it was) and I didn't check continuity with the ecm (for I still need longer multi-meter leads).
would a bad evap csps (control system pressure sensor) cause/allow the suction i'm seeing through the canister especially at closed throttle? or is the sensor giving an out of expected reading (when the engine control monitoring system is trying to do a evacuation test of the evap system) because the canister vent valve isn't closing and hence the suction through the canister (while it's trying to do an evap system test?)?

surban1

iTrader: (17)

I've been playing a bit more with this issue this morning and have some info and some questions.
now when I disconnected the vent canister connector, I immediately got a code p0446...combined with my observations that the valve is working properly when off the car & 12v applied to it and that the harness connector is supplying 12v, does this mean that the vent canister control valve is working ok?
does anyone know if when the pressure sensor fails, does it cause the evap canister purge volume control valve & the evap purge control solenoid valve (and therefore the evap purge cut valve) to be "open" so that there is constant suction through the canister (even at closed throttle/idle)?
i'm going to try to block off the canister fresh air intake and see what codes I get and will report back. thanks for any help.

Fakie J Farkerton

iTrader: (51)

I'm sure the above questions are answered in the FSM troubleshooting.

surban1

iTrader: (17)

I read through the ec section again (especially the relevant parts) over the last week+ and I haven't found answers to those two questions; hence why i'm here hoping that someone who's either had themselves or worked on a car that had the same or similar issue would weigh in with their knowledge.
I have seen in the fsm that the purge line should be shut during closed throttle...but that's not what i'm seeing. that's what makes it extra weird (on top of the regular weird that evap stuff normally is).

i'll have emission coming up over the next 2-3 months and want to be ahead of this shenanigans so that Illinois doesn't put the screws to me. it's hard to do any work on the car where i'm now living and i'm time constrained so that doesn't help either.
i may just get a used pressure sensor (and maybe the harness connector also) because once I have the opportunity to get the old one off, I may just put new one on (and have new harness in case I fnd that its bad) but I dislike throwing new parts on hoping that will solve the problem without really understanding the issue or knowing what's really wrong. I typically try and troubleshoot (and learn) before replacing but I may have to take a different tack this time.

surban1

iTrader: (17)

I ordered a replacement used pressure sensor & harness and should have it by next week.
in the meantime, I blocked off the canister vent control valve air intake while leaving it plugged into its harness connector so that it couldn't suck fresh air in through it and shortly thereafter (while just letting it idle for ~ 5-10 minutes) got a code p0446. when I removed the stopper from the canister's vent control valve's fresh air hole, I could hear that it had and was holding a vacuum inside. since the fuel tank is holding pressure (can hear & smell gas vapor escape when open the fuel filler cap) and the purge line is holding vacuum (from the above test), it seems that there are no leaks in the evap system and I will just switch out the control system pressure sensor when I get the new (used) one. i'll report back when I've switched the part that the original code p0450 said was bad.

surban1

iTrader: (17)

still no joy for after i put on the new (used) pressure sensor i still got the p0450 after the big disappointment I tested the old one with vacuum, a 6v (I didn't have a 5v) source and the new (used) harness connector that I also just got and the old one seems fine.

next i'm going to check the harness on the car (finally got longer multi-meter leads) for 12v and ground and report back when I know something.

while just investigating around trying to figure out something on this damn evap shenanigans i'm facing, I noticed that once it starts sucking through the canister is when it trips the p0450 code and that if I take off the vacuum hose that goes from the evap canister purge control solenoid valve to the evap purge cut valve (both under the hood and that interplay with the evap purge volume control valve) that the sucking through the canister stops. my post from a few days back where I suspected the purge control solenoid valve may be the culprit. i'm going to check that out also for, according to the fsm, there should be NO vacuum between those two when at closed throttle. i'll also report back on that.

but if anyone has any helpful tips, clues, input or whatever...PLEASE post and let me know for this evap issue is really starting to get to me.

fyi, maxima_joe has been a great source for tested used parts (and some good tips & know-how also) with good items and good prices.

surban1

iTrader: (17)

resolved.

the pressure sensor harness was also fine. it was the evap purge control solenoid valve and or the evap canister purge volume control valve. I believe that the solenoid was working/getting stuck open intermittently but I messed up the control valve while trying to disassemble it and had to replace both parts...so i'm not 100% sure which one was the culprit (it may have been both) but the solenoid very likely seemed bad near for sure and the control valve may have contributed (but less sure about that). I just knew that it shouldn't have been sucking through charcoal canister will at idle!

haven't had any more evap codes since replacing both of those parts (under the hood) and car odb shows that the evap cycle has run (ie evap system show "ready"). thanks for input and hopefully this info helps someone else in the future.

TurboA32

iTrader: (36)

If your code happens to come back you can get a 95 federal emissions ecu and that will solve the problem. It looks like you have a 96 max from your sig so it should be a easy swap of the ecu and thats it