Rough Idling/Stalling, all 6 cylinders burning super rich, please advise.

quattro527 · #1 10-20-2005, 04:44 AM

So I've replaced all 3 ignition coils and wires, as well as new plugs (gapped at 0.060 as well as 0.040 as an attempt to reduce the missfires) to try to solve my rough idling/stalling issue, but still no luck.

I ran the car for codes last night, and got P0306 (Cylinder 6 missfire) and P0300 (Random Missfire). After 50 miles on these new plugs, ALL SIX came out completely carbon fouled from the richness.

When the car is driving, it feels absolutely perfect. Only at a stop when it's idling, the idles would hesitate and the car would hickup, sometimes even stalling when the revs drop too low. I've just about replaced everything on the ignition side (except for the ICM, which is said to with WORK or NOT WORK completely), but the idles will not stablize. I believe the idle and missfires is bad due to the rich mixture (flooding of the combustion chamber), and looking at all 6 plugs being soaked in carbon tells me it's defintely something else.

I havn't had the time to test the injectors yet, but could a SINGLE (or or more) injectors cause ALL SIX plugs to foul?

So far this is what I've done:

Cleaned out EGR
Tested and confirmed MAF is working properly (also tried tapping it)
Replaced IAC
Replaced all coils
Replaced wires
Replaced plugs (2 sets in the last 100 miles from them carbon-fouling)
Performed the Idle-Relearn

...I have still yet to try the injectors, but I'm still looking for a cause as to why all 6 cylinders would run so damn rich..

If anybody has another solution I can try, please let me know. This is starting to get frustrating, especially when the car would stall off the fwy offramp, and I would have to crank the car for 10-15sec to get it started in neutral, than manage to put it in D and powerbrake just to keep the revs up so it wont stall on me... [

]

Thanks

Jeff

Schurkey · #2 10-20-2005, 08:23 AM

What engine?

What year?

maxwedge · #3 10-20-2005, 09:23 AM

Fuel pressure in spec?

quattro527 · #4 10-20-2005, 11:40 AM

Sorry... 98 3.1li SFI

richtazz · #5 10-20-2005, 01:27 PM

to answer your question, each cylinder has it's own injector, so one bad one can't make all 6 cylinders run rich. Your problem sounds like a faulty fuel pressure regulator to me, and a fuel pressure test will confirm that.

quattro527 · #6 10-20-2005, 01:46 PM

Quote:

Originally Posted by richtazz

to answer your question, each cylinder has it's own injector, so one bad one can't make all 6 cylinders run rich. Your problem sounds like a faulty fuel pressure regulator to me, and a fuel pressure test will confirm that.

Someone has also added something to the "To-Do" hit list:

ECT (coolant temp) sensor. Though it appears to be working on the gauge, it DOES read a lot lower than normal (always at 1/3, which flutuates to 1/2 at times). Another possibility?

I will have the FPR checked out as well.

cadgear · #7 10-20-2005, 03:36 PM

The ECT has a bearing on the mixture, but have you checked into the O2 sensors? Those determine whether you're in open or closed loop mode. If the sensor is shot, you could be staying in closed loop and thusly running slightly richer.

MAP sensor? If the MAP is indicating to the PCM that there's low vacuum (high throttle/load), it could be dumping more fuel into the motor. This, combined with O2 sensor readings, could make you run rich.

As far as ICMs go, there's grey area. Some will work, some will halfass work when they're failing, and some will not work at all. My 1991 Cutlass died once at an intersection, when my light turned green I went to give it gas and it died on the spot. The shop couldn't replicate the problem, it turned out I could drive it all the way to the shop and back three times (roughly an hour of driving) no problem. When I went to pick it up, however, it died 400 feet from the shop.

quattro527 · #8 10-20-2005, 04:22 PM

Quote:

Originally Posted by cadgear

The ECT has a bearing on the mixture, but have you checked into the O2 sensors? Those determine whether you're in open or closed loop mode. If the sensor is shot, you could be staying in closed loop and thusly running slightly richer.

MAP sensor? If the MAP is indicating to the PCM that there's low vacuum (high throttle/load), it could be dumping more fuel into the motor. This, combined with O2 sensor readings, could make you run rich.

As far as ICMs go, there's grey area. Some will work, some will halfass work when they're failing, and some will not work at all. My 1991 Cutlass died once at an intersection, when my light turned green I went to give it gas and it died on the spot. The shop couldn't replicate the problem, it turned out I could drive it all the way to the shop and back three times (roughly an hour of driving) no problem. When I went to pick it up, however, it died 400 feet from the shop.

The most frustrating part of it is, the ONLY codes I am getting are ignition/missfiring related codes only. Nothing on the O2 sensors, or anything else.

maxwedge · #9 10-20-2005, 05:22 PM

You can't check the coolant temp sensor on your dash gage different unit, scan and look at the temps, as Rich and I said also check fuel presssure.

quattro527 · #10 10-20-2005, 05:33 PM

UPDATE

I managed to play w/ the vacuum lines during my break today, making sure they're all intact while the engine was running (and idling like crap). I then decided to pull the vacuum line that is connected to the FPR. The minute I did that, fuel came squirting out of the FPR's vacuum end!!!

I have no clue about this car, but I DO know that the vacuum controls the inner diaphram that restricts/opens fuel pressure...and if fuel is leaking out of the vacuum end, that diaphram is most likely destroyed, cause ZERO regulation of the fuel pressure during idle and making my car run rich.

I found a FPR at my local shop, and will pick it up on my way home... hopefully THIS will fix my problem.

maxwedge · #11 10-20-2005, 05:54 PM

Well, that's what we've telling you, anyway good deal, now change your oil also.

cadgear · #12 10-21-2005, 12:48 AM

Its not just that you had no regulation, but if you're sucking in that fuel..well. Go figure, you've got an unregulated amount of fuel entering the engine that the PCM can't compensate for.

The 3800s had an FPR recall that's still open, we get a bunch in every week for that.

DOUG997 · #13 10-22-2005, 05:07 PM

Maybe You Guys Can Help Me. I Have A 91 Lumina Z34 With 93,000 Miles On It. It Stalls At 4 Way Stops Just As I Am Nudging Up Waiting For My Turn To Go. Once I Drive Or Accelerate Eveything Is Fine. But As Soon As I Go Gas, Brake, Gas It Stalls, But It Starts Right Back Up. The Rpms Correct At The Normal Idle, But Runs A Very Little Bit Rough. I Brought It To My Chev Dealer. They Diagnoised A Vacume Leak And Engine Is Not Getting Enough Air. They Replaced All The Intake Gaskets, Then They Replaced The Fan Motor Because It Was Drawing Way Too Much Amps When It Kicked In, And Then The Said The Timing Was Off And They Re Timed It. Once They Re Timed It, It Had A Lot More Power, But Still Stalls After Being At The Dealer 3 Times. The Dealer Told Me This Is One Of The Worst Cars Chev Made (1st Year With This 3.4 Engine) And The Hardest To Work On. I Do Not Know What Else It Could Be. They Tested The Fuel System And All Is Fine. Help!!

maxwedge · #14 10-22-2005, 07:25 PM

So after did all this work now they beg off saying this is a hard engine to work on?! I'd drop it back in there lap and say maybe you will fix this or find a way to disput the charges. Anyway, lots of issues here, dirty or malfunctioning IAC, sticking egr, dirty throttle body, this needs on site analysis.

POST REPLY TO THIS THREAD