Noodlez

After many months of trying to figure my misfiring issue out on my 03 Base (150k miles) , I believe I have narrowed it down to a electrical/ecu issue.

Here is a list of everything that I have done:

- Cleaned MAF
- Cleaned Air Filter
- Checked for Vacuum Leaks
- Checked for Exhaust Leaks
- Replaced Spark Plugs
- Checked Coil Packs
- Installed Brand New OEM Valve Covers
- Installed the 5/16 plenum spacer from Motordyne while the plenum was off

Mods

- Motordyne Plenum Spacer
- K&N Intake

Electrical?

The reason I believe that my issue has something to do with the cars electrical or ECU is because my issue is so intermittent. Completely randomly upon start up, the car will run completely fine, while on the other half, sometimes the car will misfire.

Sometimes the rough idle during misfire will ease out the car will seem to "snap" back into all cylinders and run completely fine. During this process I get a flashing CEL. However, if the CEL is flat on, sometimes the misfiring will stop. I ruled out anything else because the car will run fine half the time.

Codes Pulled

Only code I have been able to get is of course P0300. Which makes sense because when it is misfiring, it is completely random. But sometimes it runs fine!


If anyone has any insight on what you believe my problem is, feel free to leave a comment! I'm taking the car to a local shop to diagnose the problem more thoroughly on Monday. Will post results then.

Thanks for the help!

coletrickle74

iTrader: (1)

Did you check injectors?

Also, if it's intermittent I'd check all your wiring; sensor plugs, grounds, etc. Maybe something is loose and making bad contact.

dkmura

iTrader: (64)

Also, how long have you owned your Z? When did this problem first begin happening?

Noodlez

Did not check injectors yet, didn't make sense to me because I figured if one was clogged it would have constant performance, while my problem is intermittent. Checked all known grounds. Checking all plugs with a multimeter tomorrow.

Noodlez

Owned since last October. No record from previous owner. Problem started around a month ago, I had oil in 2 of my spark plug wells and was hoping the new valve covers would fix the problem. If I don't find anything after checking all plugs and connections I'm hoping my local shop can find something I'm missing.

coletrickle74

iTrader: (1)

Sometimes a different set of eyes finds something obvious. I had a Charger that had a slight miss due to clogged injectors. I ran some injector cleaner through it a few times and it smoothed it out. Not sure if that's common with the VQ though

rancor

Maybe check the injector harness there is not much else to do.

NOSDEVIL

iTrader: (1)

Omg man I am having the same issue with the same year and miles...only difference is I have a utec and car is boosted. Mine is cylinder 3, I checked all what you did and I found that there is continuity to the coil and ground however the coil is not receding any communication from the ecu. Not sure if it is the ecu or utec ....

Noodlez

Well, after an unexpected solution, I finally got it to misfire long enough to do a proper test of the coilpacks. Interestingly enough, the coilpack that was bad, seemed fine just weeks before another test. Guess this proves that coilpacks don't just die and stay dead! I'd been told that once a pack goes its gone. Apparently not! Car seems to be running just like normal again! Still not sure why I never got P0302 because the only faulty pack I found was cylinder 2... Oh well! Thanks for the ideas guys!