I've been having a stumble and miss under certain loads in my 94. i've gone through 3 sets of wires and 3 sets of plugs so I'm eliminating that as the probable cause. The found some interesting things on the snapon scanner. all sensors look normal, including a perfect blm reading. but here's the weird part...I'm getting a torque converter code on my M6! I don't remember the code excactly, but i'll check again. (this is, and always has been an m6...pcm included).
my opti is a new gm unit about 2k miles old. i've tried doing checks on the vent harness (i have the 95 vented opti system), but nothing has come up that would give reason for the opti spark to fail. This is where i am confused.
my symptoms: stumble, miss, light backfire, loss of all throttle reponse under certain loads at certain rpms. it typically does this in lower rpms, but sometimes in the mid range. it has NEVER done any of this when you get on it 3/4-WOT. runs like a peach all the way to redline. i had it dyno tuned and it ran smooth on the dyno for all 3 runs. a/f and spark was tuned perfectly and pulled 12.5:1 a/f all the way through. adding weight to the car or driving up hill greatly multiplies these symptoms. All of these symptoms vary greatly. some days the car barely gets itself anywhere, and some days its barely noticable. weather doesn't seem to change anything.

these symptoms are typically not opti symptoms, right?? ICM, and accel coil are also new and tested fine on a DMM. so, if its not the tune, not the plugs or wires, icm or coil, what else is it? this thing is really kicking my ***! is there any way to test the opti for sure?

 

anybody?

 

Sure there is. You can put all 8 wires on a scope and see how each plug is firing. Thus eliminating the spark portion of the opti. You can also look at the 2 feedback signals from the opti to see how they look with an Oscope (I use a Vantage).

I have a question for you. Is the problem from dead cold or after it warms up? If it is after it warms up, have you tried unplugging one of the O2s to keep it in open loop and see if it runs better?

 

i do have a vantage. i never thought of using that. it's hard to say anymore if it does it or not. but todayi used the tech 2 and it told me the car is in in open loop all the time. if i manually put it into closed loop via the tech 2, it runs like crap and my short term fuel trims on both banks drop quickly from 128 all the way to the mid 70's and the car then dies. that tells me it's leaning the **** out of the engine to the point where it can no longer run. weird part is that all the sensor input readings are normal. nothing out of wack. may not be a spark issue at all, although i'm getting an opti low voltage AND high voltage code.I'm also getting a pcm malfunction code. since all the sensor inputs are good, this leads me to believe the pcm is bad and putting itself into open loop. I'm assuming that when the car is stumblnimg and sputtering (sometimes dies when coming to a stop) the computer is trying to re-enter closed loop operation, but it can't do it and then sends itself back into open loop. this thing would not run any longer than 30 seconds in closed loop before it dies of fuel starvation. I'm looking for all kinds of reasons for the fuel not to be there, but everything is normal. my maf counts are a little questionable at 14 g/s but that seems to be ther magic number between the 2 maf's i have tried. So what else can cause the short term fuel trim to drop like that???? a bad pcm??? btw, the car runs okay in open loop. a little rich though.