Shawn W

I bought another Z28 today. I think i am going to replace my vert. It's that medium blue color and a hardtop. Anyway it runs like crap when it is cold. It misses and pops and idles really rough. Doesn't have much power at all. If i keep driving it untill the temp gauge is a little above the 160 mark the SES light will come on. As soon as the SES light comes it it runs 10x better. I guess it is going into limp mode at that point and stops reading some of the sensors. I am thinking maybe a bad 02 sensor although i have never seen one make a car run that bad or opti cause it's just crap anyway. The car is a 94 with the unvented opti. Give me some clues as to what it could be.

Thanks
Shawn

chasmanz28

lots of things, replace the cheapest things first, fuel filter, wires, plugs, coil, then see how it runs, then if all that fails change the opti

shoebox

Don't guess, get it scanned.

Shawn W

well i don't think it's the plugs, wires, fuel filter or anything like that. I mean the second the SES light comes on it gets a lot better almost like there's nothing at all wrong with it. As long as that light is off it runs like crap. It has to be electronics. Just gotta figure out which one. I am going in the morning to have it scanned. Something makes it run like crap as long as the computer is in closed loop( warming up) mode. When it warms up and goes to open loop it throws a code and probably starts running of of pre programed tables in the ECU instead of the sensors. At least this is what i am figuring. Tell me what you guys think.

Shawn

shoebox

Just to clarify, open loop is at startup and closed loop is after it warms up and is reading the sensors.

Shawn W

yeah i mixed those up didn't i. Anyway on most cars whenever they get warmed up and start reading off sensors. If they encounter a bad sensor theay will return to readind from the ECU instead of the bad sensors. Kind of a failsafe mode. My SES light doesn't come on till the car aparently start reading off it's sensors in closed loop mode. When it warms up(and SES light comes on) it runs much better. It must be something screwing with it in closed loop mode. Bet it's going be a biatch figuring this one out. I figure it has to be electrical though because at the same second the light comes on the car imediately start running much much better. Hmm if it is reading of mainly the ECU in open loop mode maybe i should try switching ECU's with my other car. Can anyone else tell me what sensors input vital info during warm up (open loop) mode. It has to be one of them or the ECU.

THanks
Shawn