Well, after going through most of the ignition, it finally started to throw codes. I ran a scantool on it and got P0335 CKP circuit problem and P0336 CKP signal out of range. I replaced the crank position sensor and that didn't work. I discovered a wire loom that was too close to my LT's and the plastic loom is partially melted. I know this could be a contributor to the problem, but here's the wierd part: the car will run well until it gets warm(usually 2-5 minutes), then start to surge and buck. If I would use a scantool to tell it to run in open loop, it runs better. Then last night I drove it after it sat for 3 hrs. Using the scantool I had it in open loop and it ran crappy right away(cold). I switched it to closed loop and it drove fine....

This makes me think it's a PCM problem.

If so, is there a way either reflash my pcm or download the tune off it and load it onto a new pcm without going to the shop that tuned it?(they are an hour away)



Matt

 

hey man i have the exact same problem as you right now. i dont have no scanner tho. let me know if you figure it out. mine has been doing it most of the summer. just once it gets warm it will start to do it. also does your check engine light start to flash on the highway? my car is also a 1996 z28 m6

 

Yes! When this problem first arose it did that. I tried scanning it with a code scanner from checker, but there weren't any codes. Initially on a scantool it would read misfires, so I thought it was ignition. Went through almost the entire ignition system when it finally set a code.

 

anyone?

 

Bad 02's?

 

nope- both are working well

 

I drove the Z to my buddy's house to return his scantool. On the way over there it ran like crap again. Didn't have the scantool plugged in. He wasn't home, so I left- but before I did I plugged in the scantool. Started the car, made sure it was in closed loop, and it ran great the whole way home. I even drove a few blocks xtra just to make sure. Even unplugged the scanner while driving. No problems...

Very odd.

 

i was also running good cold and bad hot, good 02 sensors. im currently going through it all, new accel opti, MSD wires, and NGK plugs. ill let you know how i do.

 

That sounds like the same problem I was having with my old opti. It ran fine cold, but once it heated up, it started missing so bad it would stall. Went through everything before I finally replaced the opti. Ran perfect after that.

 

thats good to hear cause im changing my opti as we speak.

 

Yeah, opti was the first thing I suspected. So I changed it but it didn't help.

 

i did my opti and found some borderline bad wires, so i replaced the wires and the opti, plugged a couple vacuum lines that were still there from the AIR and EGR, re-wired my 02 sensors(sodered instead of connectors this time), did the TB bypass (was all apart so i said why the hell not) and now it runs MINT

 

My car does the same thing, drives good cold and bad warm. It also throws a po336 code. I've asked around if the crank sensor effects performance, and some people say yes and some say no. I had it tuned out of the pcm and it still drives bad. 96SilverZ did yours start acting up out of nowhere, or was it after a modification?

 

Mine started doing it out of nowhere. I don't see how you can tune the crank sensor out. Doesn't it need a signal from the crank sensor to determine timing? Mine for some reason doesn't want to go into closed loop. If I tell it to using a scantool it runs great.

I'm going to get my partially burned wire harness fixed. If that doesn't fix it I'll reflash the PCM.

 

Thats exactly what I say say, it needs a signal from the crank for timing. It would'nt be there for nothing. A couple of well-known mail order tuners say that its there for emmisions only. Mine started acting up after the cam install. I've replaced the crank sensor and it still throws the code, maybe the reluctor wheel? I havent checked the wiring, but it does run close to the headers. I've aslo noticed on mine, it runs waaaay better with the O2s unhooked(new delco O2s). Does your car run lean?