My '01 Z24 just rolled over 200k miles on the odometer, with no major issues. She's still sporting the original clutch, water pump and timing set!

Unfortunately, things have now changed for the worse. There's a nasty misfire on acceleration at low rpms and I just pulled a P0300 code. Is this typically an ignition issue or head gasket issue? With this many miles it could be a number of things, but a bit of forum searching pointed to these two possible causes.

Well lots of things.

A head gasket, very doubtfull, that also comes with white smoke out the exhaust and loss of coolant

How long has it been since you did plugs and wires, the coil pack is a possibly.

Typically a random misfire is caused by an ignition problem, a fuel problem typically doesnt set the check engine light but has more driveabaility issues.




- 2004 Cavalier - 124k, owned since new

Plugs have been replaced fairly recently, with a fresh set of boots as well. Going to pull/inspect plugs and test the coil packs.

I have had some coolant loss, however, it's been minor and I haven't noticed the tell-tale sweet exhaust smell or white exhaust.

hey i got the same exact problem 98 z24 167,XXX....been trying to look for answers also.....someone mentioned the timing chain.....???? anyone else agree??? the exhaust smells like unburned fuel real bad!!!

Pulled the plugs and cylinders 2 and 3 were extremely fouled. Looks like a bad coil pack.

Going to go the extra mile and replace both coil packs, coil cover and plugs.

I can almost guarantee that the coil cover is the problem. My car did the same thing to me.

Now here's the real kicker. GM has recently changed manufactures for that part. The dealer would replace the part, and a few days to a few months later, the problem would come back. Replace the part again, same thing. I think they have now put 6 different coil covers on my car. The last visit I saw they called the Tech Assitance Center and they advised them to put a coil cover in that was the old part number/ manufacturer. They had to overnight the part in from another dealer. So far so good.

The part number that is on my car now is I believe 10475706. A search for that part number pulls up the new housing p/n # 19166100. Don't put the new P/N on your car!

I don't know who the new manufacturer of the coil cover is. My recommendation would be to call your dealer, see if you can find out, then avoid it. If you look it up on Rock Auto, I would avoid the Delphi and ACDelco parts.

Hope this helps you guys out and saves you from the frustration I have had with my car for the past 9 months.

Oh yeah, DON'T DRIVE THE CAR WHEN IT'S MISFIRING THAT BAD!!! It plugged my cat just for the short time it was running. That is not a cheap fix.

I changed the coils/spark plugs and all that and the 02 sensor.....still misfires. One guy told me to check the timing!?!?! ive had the code for about a month or 2 and still have to drive it everyday....(only ride right now) can it cause anyother damage like internally???? really dont know what else to do!!!!

check fuel injectors they can cause a misfire also

Just a quick update. The coil pack that handles cylinders 2 & 3 was bad and was replaced, the other pack tested okay. The coil cover tested out okay (continuity check with a multimeter), so I didn't bother replacing it. The car runs great again!

can the timing cause misfires? i have changed coils, spark plugs all that...........also can a misfire ruin internals???? i need help any ideas????

yes incorrect timing can cause misfires and yes misfires can ruin internals if its bad enough

Its not really that bad tho....like its not Knocking or anything the exhaust just pops a lot and pops P0300 codes all the time! ...kinda hard to explain! how much is an average cost to correct the timing?? anyone?!

Sooo... the car still runs like crap. Stutter is still there, but it feels stronger in the low rpms.

Originally, plugs 2 & 3 were sooty/fouled and the plugs, coil pack and coil cover were replaced. Now, all four plugs are sooty and the fuel pressure regulator leaks out the top when the vacuum hose is removed. Fuel coming out of the vacuum port on the top of the regulator indicates a failing regulator, correct? My guess is that the vacuum hose is sucking fuel through to the throttle body, causing a rich condition.

I replaced the regulator a few years ago, but I can't remember for the life of me where it was leaking at the time....

Regulator has failed. Simply replace it and your problem should go away. Fuel out of the top vaccum port means a torn diaphragm.

-Chris-



-Sweetness-
-Turbocharged-
Slowly but surely may some day win this race...