rpm4lalo

Here is the link to the graph:
http://members.isp.com/rpm4lalo@isp.com/

Just look at the dyno graph, ignore the mods list since that is a completety different car. We are just using that homepage to display the pic of the dyno graph.

The car is a 1996 Trans Am M6.
Here is what is going on. The car has a high rpm miss that almost always happens at about 4500-5000 rpms. Also if you look at the graph, the car is running extremely rich. What could cause this.

So far we have replaced the following to no avail.

ICM
knock module
coil wire
ignition coil

the car has a new fuel pump and new FP regulator
we put on a fuel pressure gauge and monitored WOT by taping it to the windshield and it was okay at idle as well. Starts great.

We also changed the plugs and wires about 4-5 months ago and we recently started checking the resistance on the wires and they checked out okay. The plugs seemed okay but they of course no longer looked brand new.

What is a stockish LT1's AFR normally. What could be the problem that is would break up like that and be running so rich.

We searched this quite extensively, but they all say it is a plug wire, plug or opti.

Any ideas on what we could do next to trouble shoot this high rpm miss?

turbo_Z

This is just a shot in the dark but Id look at the opti next. Looks like its the only part you have left to replace.

Zeueses 97 RamAir

mine looked the same its the opti feels like the car shakes for a moment. I just replaced my opti after 130, miles

Jon A

My dyno looked just like that:

http://www.jonaadland.com/NewPics3/Dyno2.JPG

Replaced the ICM, Coil and PCM. Fixed:

http://www.jonaadland.com/NewPics3/Baseline.JPG

Opti was fine.

Grims

Hey guys, I'm the guy with the car in the post. We replaced the ICM and coil, but if the PCM was bad would'nt that throw a light?

rpm4lalo

Jon A,

Was your car running extremely rich as well?

Patrick96Z28

Funny, I have already done the exact same thing as you Jon A. My lines were squirrely after 5K. It felt like my car from the 5K-6K range stopped pulling. I had a new coil and wires/plugs already, I did a MadZ28 tune and problem solved. I will dyno this summer again, but the car right now is pulling "crazy - scary" up top.

Grims

Anyone else have any ideas? If not I guess I'll give a new PCM a try....although I don't understand how a computers programming could just change to make the car run rich and miss...

Jon A

Yeah, my car was running rich as well but they all do stock. Missing at high RPM probably just made that worse.

I don't understand it either, but if you follow the sevice manual diagnostic procedures for many ignition related problems, it's "Try this, try that, replace this, replace that...and if none of that works, replace the PCM." I was actually doing it anyway to convert over to OBD I, so it wasn't a biggy to me. A lot easier than replacing an opti again....

Remember, that's just one possibility. These things are hard to diagnose. In my case, it wasn't the opti even though that was the first thing everybody blamed.

Zeueses 97 RamAir

Before you do that check it, there is a way by tapping the computer while the car is running and if it starts missing its your computer. But I would get a freinds and test it also swap it.....

rpm4lalo

What do most stock lt1's average for an afr? I did a search but all I could come up with is they average about 13.0, which is rich, but this TA's AFR in particluar dynoed in the 11's.

The AFR confuses me because the car's MAF is ported and doesn't that lean out the AFR a bit. Even before this high rpm miss, the car has always run rich. Just wondering if we may have more than one problem.

LT1iFiEd

My car does this same exact thing,Its sux!!Can't figure out what the hell it is.Damn LT1's and their stupid gay ignition problems

Grims

then i guess if no one has any other ideas ill go buy a new pcm..

Robs97Z28

have you ever cleaned your maf?

LT1iFiEd

Now when u all are suggesting a new pcm,by this do u mean a new pcm altogether or a dif. pcm with dif. tune?