2002 LS Misfire PO301, PO306

[aharmon]

Help. I have enough knowledege to be dangerous. My 2002 v6 ls has two codes (PO301, PO306). First noticed misfire during rainy conditions (orginially PO306 only). Replaced plugs and COP. Appeared to solve problem for short period of time then misfires started again. Now started missing regardless of weather. Checked wires to COP and appear good. Noticed oil in plug well and replaced valve cover gasket, replaced plugs (fine wire OEM's) again and COP for cylinder 6. Also moved COP's around without change. Changed fuel filter. Fuel pressure 21psi?? Now I have misfire in 1 and 6. What is the correct fuel pressure for a v6 3.0l LS? Any ideas would be appreciated. My next thought would be injectors but dont want to keep throwing money away....

[shorod]

I don't have the service manual in front of me, but I suspect that fuel pressure is about 2 to 3 times lower than it should be. Are you sure your gauge was installed correctly and not leaking? Your 2002 V6 has a returnless system so the pump uses PWM to regulate fuel pressure, but your rail pressure should still be higher than that.

Do you happen to have access to a scan tool that will allow you to monitor short term fuel trim? Even better, one that will let you shut off one injector at a time and determine if cylinders 1 and 6 are contributing would be great. Did you clear the codes after moving coils around and replacing the plugs?

-Rod

[aharmon]

Rod,
Thanks for your response. Sorry, I don't have a reader that will give me the ability to isolate injectors. I believe i'm checking fuel pressure correctly but I will confirm pressure tomorrow morning along with compression pressure. If it is a low fuel pressure problem would the missfire be constant in the same cylinders?
When this first started the misfire seemed to coincide with rainy weather so I was thinking wiring but have been unable to locate any obvious wire issues. Now the misfire is constant. I have cleared the codes and the same codes keep appearing.

[shorod]

Per the factory service manual, the fuel pressure, KOEO and KOER, should be 30-65 psi. I would not necessarily expect a misfire on the same 2 cylinders due to low fuel pressure. However, assuming you are measuring correctly and the gauge is accurate, you know there is a pressure issue so you may as well fix that first. The fuel filter generally is not too difficult to replace on the LS. You will need to jack the car up on the driver's side front, support it on a jackstand, remove the wheel, then remove the wheel well liner. This will give you good access to the fuel filter.

-Rod

[aharmon]

Rod,
Good news. I went back to square one and moved COP's around again. Didnt think I would need to do this since the old COP's I reused were working when I started the job, just reused in different cylinders. After finding the one in cyl #6 was bad and replaced it, I removed the plenium (?spelling) and replaced COP on cyl #1 which cleared all codes and misfires. Surprised a prior working COP would go bad. After speaking with you, I went and checked compression and fuel pressure which was good, prompting me to start at over again to see what I missed. Thank you for taking the time to help me out.
Alan

[joegr]

Originally Posted by aharmon

Rod,
Good news. I went back to square one and moved COP's around again. Didnt think I would need to do this since the old COP's I reused were working when I started the job, just reused in different cylinders. After finding the one in cyl #6 was bad and replaced it, I removed the plenium (?spelling) and replaced COP on cyl #1 which cleared all codes and misfires. Surprised a prior working COP would go bad. After speaking with you, I went and checked compression and fuel pressure which was good, prompting me to start at over again to see what I missed. Thank you for taking the time to help me out.
Alan

My experience, as well as that of many that I know is that when one COP starts to fail, it is best to replace them all. Otherwise, you'll be replacing one or two a month until you do.

[shorod]

Especially on the V6 since it is not a simple task to replace coils 1 through 3.

Alan, congrats on getting the misfire fixed. Are you planning to look any further in to the low fuel pressure issue?

-Rod

[aharmon]

Rod,
I believe I checked the pressure wrong the first time. First I checked it with the key on, engine not running and had around 20 psi. When I checked it running I got 38psi. Vehicle is running great now, fingers crossed. Thanks again for your help.