2001 LS V8 runs rough cold, fine when warm

OK... Since this thing is put to bed every winter,,, I will ask if it is stored in a climate controlled setting??? Reason asking... you said the fuel filter looked like crap when you changed it. Keep in mind that any petroleum product will settle on top of water. Is it possible that even though you have run the LS over the warmer months,,, that there is a buildup of water/condensate in the tank??? The first thing the pickup in the tank will suck up is the water
 
I have already eliminated a faulty pcm as a suspect I've checked the injector and coil driver circuits for signal with noid lights, valve cover gaskets, and plugs and coils have been replaced along with a few other things I found while it was apart. I also checked crank sensor for drops in signal. I also have checked the intake out for leaks and found none. Tho I have run fuel system cleaner through the engine I have not had the fuel rail out to actually physically clean it and replace the injectors. They are on the way, and with the fact I've had problems with injectors on a few other vehicles due to this ethanol crap fuel. I am very hopeful new injectors and a good cleaning of the fuel rail will fix it. I'll keep you posted.
 
I got a better scanner and finally pinpointed the cylinder that is assumed to be my problem. P0307 P0357

Cylinder 7 consistently is pegged as the issue regardless of moving the coils/plugs around. Even with a new coil in that spot. (8 new ones still no resolve).

I guess my next stab is pulling that injector...
 
I doubt it's the injector on that cylinder, I really do. With a P0357 fault, the PCM could very well shut down that injector.

Try wiggle testing the wiring at the #7 coil and along the wiring harness to the PCM

Read 'Possible Solutions' at: https://www.obd-codes.com/p0357
 
Andrizzle said:
...I guess my next stab is pulling that injector...
Click to expand...

Not if you are getting P0357. That's a code for an electrical problem with the primary circuit on that coil, not just misfire like P0307.
It could be the coil, the wiring, or the PCM. It seems like you have eliminated the coil as a suspect.
 
Time to break out the magnifying glass and have a real close look at the wiring to the #7 coil connector.
 
I guess I need to undo all the sleeving/black tape to fully inspect the wiring? What a mess.

I've inspected the wiring at the connector, it seems to be just fine.

Also want to remind, that my issue resolves by the time the car has reached operating temperature. Would a PCM/wiring issue behave like that? Reading the past threads on the people who replaced the PCM, it seems they had a constant misfire.
 
It is certainly possible (but not certain) that there is an electrical/electronic issue that resolves as the components heat up. Actually, this is fairly well known in electronics. Sometimes we even troubleshoot it using freeze spray. Still, this is all speculation.

AFAIK: Whereas P0307 only means misfire and can be caused by ignition or fuel or compression, P0357 can only be caused by an ignition problem.
 
Okay so I visually checked the wiring with lights and mirrors, and I cannot find any breaks in the engine bay area. So unless something magical happened between there and the PCM, the wiring appears to be good.

I guess the next step is the PCM. I see from searching people have used SIA to send their PCMs in for repair for about $160. But of course that means no working car for that time period.

I think I can just get a used gen 2 PCM and have a dealer flash it to my car for probably the diagnostic fee, though, yea?
 
Yes, that can be done. Note that you'll need to bring all your keys with you. You must have at least two unique keys.
Also, you need to electrically test the wiring for high resistance and possible shorts to ground, in addition to the visual check that you did.
 
I have a DMM. Do I attempt these readings at the coil connector?
 
Andrizzle said:
I have a DMM. Do I attempt these readings at the coil connector?
Click to expand...

you have to unplug the coil and unplug the PCM, then you probe from the switched coil connector pin to the corresponding pin on the PCM connector, being careful not to damage either pin. The reading should be well under five ohms (the exact value depends on how well your meter zeros out). If this reading is good, then measure from one of the above pins to ground (metal of engine). The reading should be well above one mega-ohm.
 
Well I've replace more parts, all new injectors. Verdict, check engine lights are out, haven't come back YET, but It's still not quite right, it still has a VERY slight shake on startup. There was a change in how it starts and runs tho. Before replacing the injectors this car ran at 1500 rpm cold startup, before kicking down to 900 RPM's, and then a few minutes later down to about 750 RPM's. Now it's starts up at 1200 RPM's, idles down to 900 and then 750. Also acceleration, and shift performance has improved. Tho compared to any other vehicle I own it takes a very long time for initial idle kick down.
 
twistedwrench said:
...Tho compared to any other vehicle I own it takes a very long time for initial idle kick down.
Click to expand...

The higher idle is to warm up the engine and catalytic converters faster. Older FI cars likely don't have this emissions based requirement. Alternately, some cars use air pumps to warm the converters, so the engine doesn't have to idle higher for as long, and lastly, the smaller the engine the quicker the warm up.

I'd say that on my LS the kick down is probably only a few seconds (it's hard to be sure since I don't wait up it, I just shift into gear and go). Keep in mind, that it rarely gets down to 40 here. (In the 60s right now.)
 
Andrizzle I have seen this very problem on another vehicle. We replaced plugs, coils, inspected injectors, tested wiring..blah blah blah, Turned out to be a bad driver in the PCM. Started out with a misfire ran rough but as the temp increased the misfire went away. Most cars use a 12+ constant and a PCM delivered ground. Check your common for voltage at the coil, if you have voltage on the common, move to the signal wire, look for an A/C signal, or if you have a scope thats even better. IF you find coil signal voltage and common voltage you know the problem isn't the PCM or wiring, which would put you at broken lock tab on coil connector or bad COP, possibly a fault in the misfire monitor. IF you find no signal its time to test continuity of the signal wire and the PCM itself. Unplug the pcm connector and the coil harness test for excessive resistance between the 2, if you find excessive resistace or OL you found a damage, broken or shorted wire, trace the wire and repair, If not it's time to look for a new pcm. I will tell you tho ALWAYS replace a pcm as a last resort, in 20 years of working on cars I have replaced 1 pcm. I've owned 5 cars and a boat that "Need a PCM".....not one of those needed a pcm. I've seen broken, shorted, and grounded wires, a bad stator, and a bad ignition all diagnosed as a bad pcm.
 
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I have a few perfect PCM's that came as extras laying around for various cars....maybe I should Ebay those suckers......
 
If I get in it and go the idle kicks down by the time I hit the first stop sign, also the misfire either doesn't happen at all at higher rpms, or is so minimal I can't detect it. The pain with my issue is I have 1 chance a day to find it and fix it. I waited 12 hours last week after first warm up to restart it hoping it would act up, so I could pull a code. Of course it didn't misfire once.......PITA. looks like a minimum of 16 hours parked before it will do its cold misfire.
 
My 02 V8 is basically doing the same thing except that it's worse the warmer it is outside. During the summer when it was around 90-95F, it threatened to die on me a couple of times that I didn't let it warm up on the first time I would slow down to a stop. Below about 40F it doesn't misfire at all as far as I can tell while warming up.
 
Twisted,

The colder the weather... the longer it will take to drop to 750. That's the "nature of the beast" on a fuel injected vehicle,,, until the engine gets past "cold loop" cycle. Working the engine at low RPM's helps to get to "warm loop" faster... but jumping on the highway while the engine hasn't come up to full temp doesn't do the engine any good.

Glad to hear the problem is getting better. However,,, since it doesn't seem to be completely fixed,,, I have a couple of suggestions.

First,,, since this is an '01 LS... it has know issues with the valve cover gaskets. Make sure there is no seepage of oil into the plug wells. Even minor soaking of the plug boots can cause a misfire eventually... until the oil vaporizes.

Second... after reviewing this whole thread again,,, your problem seemed to MAGICALLY move from cylinder #3, to cylinder #7, (P0303 to p0307). This seems a bit suspect,,, and I am not sure what to make of this. There is no reasonable explanation how the misfire moved from one cylinder to another... other than a possible PCM/grounding issue,,, or worst case scenario... something else you aren't saying.

I'm not accusing... so in the best intent,,, even after you said all cylinders were at 175 PSI... I would suggest doing a compression test on all cylinders when the engine is cold... and then warmed up. Make sure all plugs have some "never seize" on the threads for easier removal to do the compression test when warm. If all cylinders read same when warm,,, then intake leak would be the next most likely possibility.
 
Drizz and Aemm,

Your issues may be different from Twisted. More info needed, (or I need to go back and read again as a separate issue).

Joe,

Not being familiar with the Gen1... could all of these separate issues be partially caused by a faulty IAC... with a secondary issues also? I know the computer can compensate for minor mechanical issues... but how far does that go??? Seems I am becoming an "old dog"... but still willing to learn and offer what I can.
 
Oil vaporizes? Pardon me? Come again?
 
At what point does a coil kill a plug? I have brand new plugs in, but since it is misfiring, I assume the plugs are being ruined from this. I guess they are cheap enough to just get another set and see if I can figure out this misfire thing.

The LS sat for 3 days in below freezing weather while I was out of town. Fired it up in 23F air this morning, and it sounded like it was running on 2 cylinders. It was horrendous. I scanned immediately and got misfire codes on 1,2,3, and 7 cylinders. This time no primary circuit codes. So I guess I am going to bite the bullet for the 3rd time in a year and a half and order 8 more f**king OEM coils and plugs and see what I get.
 
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