i have a '94 z28 with 95 k miles and is experiencing the typical lt1 stumbing. i've heard it could be the opti. however, if it was the opti that was gone would that cause the car to die every once in a while. when it does die, all i have to do is unhood the MAF sensor and it will start again. however, when it is stumbling while i am driving it, unhooking the MAF sensor does not help anything. any input would be appreciated. i have repplaced the plugs, wires, MAP sensor, ignition coil, ignition module, cap and rotor. also what are the chances that this could be 02 sensors or the catalytic converter.

 

Might look into the wires leading up to the map sensor,or vacuum leaks.My02(connectors as well)

 

My car is SD, but it would stumble after it warmed up, and lately it would crap out at different times, then restart after a minute. It turned out to be the ignition module getting heat soaked and flaking out. It got worse as time went by, and a new module cleared it right up. When I first took it off, the heat sink grease was almost gone, but re-applying some didn't help in my case, but it's worth a shot and only costs a few cents to try. When I mounted my new module, I spaced the whole coil bracket about 1/2" off the head with washers, and it stays cooler now. Can't hurt to try.

 

the reason i was wondering if it was the 02 sensors is that first off, i don't think they've ever been replaced, and i think that 95k is quite a few miles for 02's, and secondly, if i'm just sitting in traffic, not moving a whole lot, and the engine heats right up to 220 degrees and i then go to accelerate, it does not seem as bad as when i am driving and the motor is working hard. i'm wondering if that from pushing the motor and the exhaust temperature is higher that the old 02's can't handle the heat, because even if the motor is really hot, that doesn't seem to the only thing that causes it, the motor seems to have to hot and working hard for it to be really bad. this is just a theory, let me know if it makes any sense.

 

I believe the opti is more of a higher rpm studder. I think you should check into something fuel related. Fuel filter's are pretty easy to do. Fuel pump is my guess. They usually go out at about 100,000 mi.

 

i drove around with a fuel pressure tester on the car, it was putting out about 40-46 lbs, even when the car was stumbling, the fuel pressure didn't move. The fuel pressure would go up when i gunned it, so i think that that would mean that the fuel pressure regulator is still functioning properly. Correct me if i'm wrong though. As well i unhooked the vaccum line to the egr and drove around and it didn't make a difference, i don' t know if this is a proper test to see if the egr is still functioning properly. if you have any ideas on this let me know. the car had a tune up at about 90k, so i believe the fuel filter was changed, although i suppose if there was crap in the tank, it could be plugged up already. thanks for the help.

 

well im not sure but i think if you stomp it (wot) it should bypass the o2's. if you still have the stumble then you know its not that. i may be wrong so maybe somebody will correct me if so.

 

if i stomp on it, it will downshift then go like hell.

 

when you unhook the MAF sensor and the car goes into closed loop, does it take information from any of the sensors then, or does it just go with preprogrammed information. i was just curious because i have the stumbling problem and have driven around with the MAF, 02's, MAP unhooked and it didn't help anything.

 

maybe thats my problem,if i unhook my MAF sensor my car dies. should it not do that?

 

mine does the same thing, from what i know, if you unhook the maf when the car is running the computer loses the signal and it dies, that's what mine does anyway, if i unhook the maf and then start the car, it will start just fine. my problem is that the car will die on its own, and then when i unhook the maf and start it it goes just fine, however when i unhook the maf when the car is stumbling it doesn't do a thing. i put a new map sensor in, that seemed to help but didn't fix it.

 

alright, I just got my car too run hot, and crappy, well I unhooked the MAF and it STILL runs crappy, I am having the same problem as "guest" THE SAME EXACT PROBLEM!!!
So what does this mean, if my car still runs and hesitates when i unplug the MAF,
does it mean that my o2's are still good or what?

I still haven't tried spacing the ICM yet, I replaced the Coil last weekend with an MSD one, but didn't check to see if the dielectric greese was still there or not, i never messed with the ICM i just put on the new coil...
does this sound like that could be the problem, i mean seriously???
if your ICM "heats up too much" does it just get confused on ewhat to do, and make your car run crappy or how does that make sense.... I guess before i do this, i want to make sure that it is POSSIBLE for the ICM to flake out, because of heat streess, before i go in and space it and put dielectric greese on it......
let me know what everyone thinks!
EMAIL ME PELASE!!
thanks!

 

You guys cleaned you MAF yet? Helped the hell outa my car.

Joe

 

what just run sum carb cleaner in it?

 

I know a mechanic who does it but I took mine apart (the torx screws..only goes back together 1 way). You clean the bars running from side to side (the elements) with a cotton swap and alchohol. Just be careful not to damage the things (resistors I believe) in between the elements.

Joe