Getting a misfire error code

[spotawalker]

I have a 97 paseo with the check engine lite on. A little background - The #4 plug blew out of the cylinder due to stripped threads. Had the hole rethreaded, valves ground, all new lifters, all new plugs, wires, and coils.) Compression check on all cylinders was good. The car idles rough in drive but fine in neutral. This happens whether the engine was just started or completely warm. Car runs fine at higher rpms and accelerates fine. The lite came on about a mile after getting all this work done. When I check the code, it comes up as P0304. (misfire in cylinder 4) When I delete the code the engine lite stays off until the engine gets cold again. (explains why the garage thought the error was addressed). Since the lite comes on only when the car is cold, I'm thinking that the engine doesn't run properly while the computer is in an open loop. That might point to the CTS, MAP or TPS sensors, but if it were any of those, wouldn't more than one cylinder would be affected?

[mazdatech177]

sounds like carbon buildup on an intake valve causing it to stick. take it to your dealer and ask them to do a de-carbon procedure. they will probably call it a top engine clean or fuel injection service

[TheMan5952]

yea top end cleaning could help or maybe you have a bad injector that can't deliver the right amount of gas while its cold.

[UncleBob]

these types of problems are pretty much impossible to diagnose over the net. You need to get a lab scope out and test some components to help isolate the problem. I would also recommend doing a vacuum test, to verify that there is no vacuum fluxation, and if you want to get really fancy, some osciliscopes have vacuum adapters that allow you to see vacuum on the graph, which can help pick out valve and cam issues among other things.

But if you want to do some poking at it, swap spark plugs with another hole, and wires also if you can (not familiar enough with the car in question to say) This will at least remove a bad plug or wire from the options.

If it was a bad O2, or MAF or some of the other suggestions, those are all global items that would effect every cylinder, not just one cylinder. This doesn't mean they can't be at fault, but you're much more likely to get a P0300 (random misfire) with a global item

Something is wrong with that cylinder. Could be an injector, could be an ignition issue, could be a compression issue, could be a vacuum leak. Good luck on narrowing it down.

[Brian R.]

Don't post this problem in multiple forums.

[spotawalker]

Thanks, I don't think this is carbon in the head since the head was removed and a complete valve job done. I do have more info as I have been busy trying to track this down. I'm getting a P0304 error code and the car idles rough. The compression checks out 180 in #1, 2 & 3 170 in #4 (within allowed variance), the timing is good, the resistence on all injectors is within allowed parameters, the voltage at the ECM for all injectors is within allowed parameters. I noticed that when I was checking the timing that the timing light was showing the miss by skipping at irregular intervals. I switched the coils around but the timing lite still skips. I also tried putting the timing lite on the #2 wire and the same skip showed up. I was about to replace the injector(for $100+) but now I'm wondering if this is an ignition problem. I'm running out of things to check.

[Brian R.]

A periodic non-spark is certainly an ignition problem. Check the pick-up gap in the distributor. Check your ignitor if there is a test. Either of those could cause a periodic lack of spark in different cylinders. Maybe others have additional ideas.

[spotawalker]

I don't have a distributor. The ECM is controlling this. I'll try the ignitor.

[Brian R.]

No distributor? There's your problem....

j/k

[spotawalker]

That doesn't help. Don't think I wouldn't rather be under the hood of my 69 Chevelle right now with some wrenches and a timing light i/o an ohm meter and a handheld scanner (video game).

[mazdatech177]

in my experience ignition misfires are more pronounced when the engine is hot and under load... thats not to say they cant happen when cold and idling, but id say 90%+ of the time a cold misfire is caused by sticking valves. was your compression check a hot check or cold check? it will make a huge difference. dont trust an inductive timing light as an ignition tester

[spotawalker]

The engine was at normal operating temp.