so i went over to newtech in hayward to get a tune today and the car was misfiring a little bit. they stapped it on the dyno and i could not even get a run. it was missing so bad he shut it down every pass before 3500rpms. they changed my already new plug wires and nothing changed. they also pulled my new TR55 plugs and all of them looked good (as they should with only 200 miles on them). they could not determine which cylinders where misfiring or why. finally, 2 hours later before i left they used a heat gun and determined that the back cylinders on both sides are the ones missing (he checked egt and they were both 100 degrees cooler. also unplugged the wires while the car was running and idle did not change, even unplugged the fuel injectors and no change) any one had this problem before? any suggestions on what to look for? normally i would think automatically from a misfire spark plugs or wires, but both seem fine. maybe a loose ground or electrical problem? any help would be great.

btw Newtech was not responsible in anyway for my problems. they did not cause any damage or do anything wrong, please do not think i am bad mouthing them because they tried to be as helpful and as patient as possible. if you read this thanks for your help Nick

Ben

 

Had you made any recent changes prior to the dyno (headers, etc.)? Was it actually missing at idle? Have you ever changed the fuel filter?

Other thoughts:

1. Injector balance test

 

Swap the coil pack. If that doesn't fix it you might have a broken valve spring, etc. So, the valve cover will have to come off.

Speed

 

Whatever it is find it and fix it. You really don't want to put anything on the dyno that isn't running 100%. Kudos to the guy who knew better and shut it down, might have saved you some pain and $uffering.

 

the car is missing all over the place, idle and cruising and wot. the car currently has headers, x-pipe no cats, stock ti, and a knn fipk. how often do coil packs go bad?

Ben

 

Have you cleaned the K&N filter lately? If so, there may be oil residue in the MAF, which would cause the symptoms you are seeing

 

Compression/leak down tests are the next logical step.

 

You can monitor the individual cylinder misfires via an OBD-II scanner like Autotap. If you truly have both cylinders 7 and 8 not firing, then something maybe wrong with your PCM. The coil packs, injectors, O2 sensors, wiring, etc. are all independent between the two sides.

Think a bit more info is needed before we can diagnose any further.

HTH, and have a good one,
Mike

 

it is wierd that you mention the pcm being bad because it had been replaced 1 time already under warranty. unfortunately the warranty is gone now but maybe another faulty one?

are there are ground or electrical components that tie cylinders 7 and 8 together?

Ben

 

if GM had replaced my PCM I'd bring the car back to the dealer and let him tell me what it is. If it's the PCM I'm sure he can get GM it eat it under their "good will" program. If it was only one cylinder I'd also think coil pack, but not with two. I'd be very suprised if the MAF has anything to do with the problem.

 

If you unplugged your plugwires and got no change then that would tell me it was in that system. Are your wires getting any spark? Take them off the plugs and take a look. Like what was said before, if only one cylinder I would think a coil pack, but 2 cylinders? I'm a little stumped. Keep us informed on anything you find out...



Josh

 

Throw a timing light on the bad ones and see if their sparking. Then use a screwdriver against the injector(s) to try to listen for the pulsing. I can't believe a miss that bad not setting a a P03xx code.

 

Take the car over to Synergy Motorsports in Fremont. They have a Tech 2, and should be able to scan the car and diagnose the problem fairly easily.

Theres no point in throwing parts at the car with no idea as to whats wrong.

 

yeah i had the same problems that you have and came to find out it was a broken valve spring.. hope its not that good luck

 

so i was looking at the car today and checked all the wires and everything looked good, checked the coils and they were getting spark, checked the plug wires and they were good too. finally i decided before i take it to a place and spend $250 plus, ill change the plugs and see what happens. funny thing is now the car runs great. no more misfires at all. idles nice, i took it on the freeway at 25mph is 4th (under 2k rpms) floored it all the way to 110 or so and it ran like a champ. ( i did this cause this is how he dynoed it.) turned out that 2 of the ngk tr55's were bad, but still looked perfect. in the end it cost me $20 and a couple of scars on my arm. i am very happy that nothing serious is wrong!

thanks for all the help guys
Ben

 

Good news man. glad it was a simple fix. I was also thinking about the wire getting all the way on the plug when I was reading your post. Sometimes we forget that new parts can be bad from the beginning.

Josh

 

Ben,

Great news! Interesting that the two plugs closest to the firewall were bad. I know that the ceramic can crack internally to the plug and short it out: I wonder if whoever put them in before put some kind of side load on them that cracked them.

Congrats again on getting her back up and running!

Have a good one,
Mike