Help!!! Misfire issue [Archive] - Forum


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11-12-2012, 11:30 AM
So here's the story, About 2 months ago I have the plugs and wire's changed out for a typical tune up (The number 5 plug was cracked in 1/2), then a coolant System flush as suggested by the mechanic because of the muddy coloring. Anyways, I go to start the car up and it's bogging down (Only in the mornings when first started, or after sitting for a long period of time.) Usually for 30 seconds-a minute, during the start up the RPM's rev themselves up between 1.5 and 2.5, when it's finished it seems to idle around 1. When put on the machine it shows that number 1 and 5 are misfiring and the O2 sensor needs changed. So process of elimination. I change out the number 1 and 5 coils (Nothing different) then changed out the module (temp fix for a day or two then right back to the misfire) Could the O2 sensor cause this?

So i pulled the wire's from the coils while the cars running to see if there was any change in the engine, and they sparked just fine. I've had it to one garage 3 separate times, and they have no idea what's wrong with it. I sent it do have a scope done at the dealer and they come back saying they can't find anything wrong with it.

I've searched all over the forum and find people with similar problems but no one ever comes back with a solution on how/if they fixed the issue. I'm really out of options so ANY ADVICE WILL REALLY HELP PLEASE!!!

11-12-2012, 03:36 PM
What codes are you getting ?? Also what plugs are you using ? These motors are kinda picky on plugs AC delco Iridiums are the best What are they gapped at ?
The 02 sensor is going to skew your fueling and cause a misfire also
Continuity check your plug wires also

11-12-2012, 05:16 PM
Could be a lot of things. Are you getting any DTC codes?

Also pulling the plug wires from the coils while the car is running is a bad idea. It's a waste spark system, meaning it fires both cylinders on the coil at the same time so they get spark twice per cycle. That's a lot of energy, and it has to go somewhere so it will still jump to the engine down the outside of the coil if you pull the plug wire off. I tried it once and could see it happening. Good way to maybe burn up the ICM or a coil, plus it shocked the **** outta me!

Misfire could be from a bad plug or injector, crank sensor issue, plugged cat, etc etc. High idle can be from a vacuum leak, faulty IAC valve or TPS sensor, MAF sensor, etc etc. It can be a lot of things.

11-13-2012, 06:44 AM
The code coming up is a P0300. And I put in Brand new AC Delco's, Last night we went back over all the wires and coils and found no issue there were no misfire's showing on the machine, but you could feel it in the car, so
We ran a fuel injector cleaner and it seemed to do the trick, But then number 6 showed up misfiring. Pulled the plug and it was soaked in gas (We weren't smart enough to check before running the cleaner) So we cleaned it up and packed it in for the night. We're thinking it was a hung up injector and we're hoping the cleaner took care of the it considering the car fired up this morning with no issues at all and the misfire went away after we ran the cleaner. Fingers crossed that it's fixed, if not we're tearing it apart this weekend. I'll keep you updated