Car is 95 formula m6 60k Miles Full-Bolt on. Stock engine.

Car ides fine and also pulls great to 4700. After 4700 car surges. I thought my wires were just breaking down so i put a set of taylors on there and car still does it. I also removed my msd box still does it.

Car is not making knock pinging or any of those noises. I did check my KS and wireing just to make sure and thats fine. Also have put a msd coil on which didnt help either.

Car does have a stock opti though.

The thing that gets me is it runs perfect to 4700 then it breaks up.

Give me some ides to check? or is it my opti?

 

Change fuel filter lately?

Change it, if it still does it, get a fuel pressure guage, might try dumping a can of techron(sp?) in the tank if the injectors are dirty.

 

If it's not the fuel, and you changed the plugs, wires and coil, it's either the opti or ICM. The ICM is known to go bad when heated up, but if it does it cold or hot and always at the same rpm, then it's most likely the opti. I went with the MSD unit and couldn't be happier.

 

The Fuel Filter was changed prob 6 months ago and only 1500 miles. And yes it always does it a the same RPM. I have never run any injector cleaner through it. Maybe tuesday ill go get a fuel pressure gauge and check that out.

Like I said it runs perfect until 4700 rpm, then it just starts surging.

 

My car did the exact same thing. I would be 95% it's your opti, b/c I replaced wires/plugs/coil/opti and that fixed it for me. Since you already replaced everything else, man up and spend that money on the opti .

Is the ICM that thing that the coil bolts to? Ignition control module right?

 

yes and yes. I'd say 90% it's your opti.

 

High RPM stumble is almost always ignition related, the exception would be the fuel filter.

I had a 5.5K RPM stumble which was traced to the ICM, I replaced it and it was totally gone. I also put a MSD coil on it.

The ICM is the black module above the coil, only use a GM or Borg Warner replacement.

I doubt its the opti or you would have the low RPM and 3K RPM crap out.

 

How much does the ICM run? I know on most cars its pretty expensive.

Ya i read alot that people have alot of low end misses with the opti going out as well. Considering it runs perfect utnil 4700, i mean somthig is just giving out on me.

 

Usually from $60-$75.00 or so.

 

Forgot to mention i took it out yesteday after i pulled the msd box and the first run i thought it was fixed, but the 2nd pull it did the surge again. Maybe the ICM heated up and crapped out. Then the 3rd pull it didnt do it as bad, kinda wierd.

 

It probably is expensive, but just get one from autozone and see if that fixes the problem, whether it does or not, you can just return it and get what you need from somewhere else. I just borrowed someone elses to see if that's what my problem was, turned out it was my coil. It's good to have lots of friends with F-bodies, although now more and more are LS1s...

 

Well I have the same problem on my car. It does it cold too. But when I drive it for 2h straight in hot weather, it sometimes misses slighly at low rpm/cruise.

I have a parts car. I also have an:

MSD Coil
MSD digital 6
new plugs/wires
but no new opti yet
I do have an ICM from my '94 parts car. Will try that as well.

If to no avail, will buy an MSD Opti.

 

Well i just ordered a ICM from vandevere, 70 bucks shipped not bad, local wanted 102. I dont drive my car longer then a 30 mins so i have no idea about the long end stuble you get.

Its probaly my opti, so if this icm dont fix it, then theres only 1 thing left do replace.

 

Update, I installed the ICM about 2 weeks ago and it did noithing. I have bought a fuel pressure gauge and tested the car.

Key On pressure 40 pounds
Idle about 36 pounds
Driving goes up and down like it should
AT wot past 4700 when the car does surge the fuel pressure drops with it.
Some wot runs it does the surging bad and some not as much but there is always a little bit there.

The fuel filter was changed before last winter and i have only put maybe a 1k on there.

Im going to go ahead and change it again just to make sure. But there is a chance sounds like my fuel pump is partially cutting out on high rpm.

 

With an LTx its always a good idea to check fuel first, ignition components are to expensive for these cars(300 bucks for an opti wtf?) to just go ahead and shotgun to see if they are wrong, might as well try and test things 1st before you go replacing parts.

It didn't sound like ignition because you said the car surges, if it was going pop and the car was bucking and missing, then yea, probably ignition related.

Good luck.