Car is a STOCK 1994 Z28 LT1 A4

Well, I didn't want to bother anyone with my petty problem but its to the point that the car has become a parking lot ornament. I keep buying parts for it (suspension, wheels, chassis, etc.) but I dont care for the car since the problems have started.

Here's my best description of what's going on.

I start the car, it idles smooth, smooth through all RPM's, and drives fine. After 20 or 30 minutes of regular driving, the temp gets up around 190-200* and the car will just start stumbling all over itself, holds gears out to 4-5k rpm before shifting and bogging some more. All the while its backfiring, stumbling, and making a hell of a lot of noise. If I continue to drive it like this (trying to limp it to a safe place to leave it...) it gets to the point where I'm about 75% throttle and just barely creeping along... lots of backfiring and loading up.

I then park the car and let it sit for about an hour (long enough to get the temperature down) go start it up, runs just fine... until the temp raises again, then it repeats the issue. I can slow this from happening by running the A/C all the time (turns fans on... stays cooler longer) but I want to get it fixed the right way.

I've yet to scan the car because I stopped driving it all together and haven't worried about it much, but the time has come to get it running right so I can tell myself its worth keeping.


Please inform me!

Thanks,

John

 

First thing you need to do is scan the codes and post them so that folks on the board can provide you with an informed opinion.

 

Since today is Sunday I might be able to get with my friend who has CarChip and get my car scanned.

I drove it last night for about 30 minutes and got stranded at a Restaurant. After I go pick it up (assuming its still there... EEEK!) I'll try to get it scanned and get back with everyone.

 

Optispark is going

my Opti is bad right now when it heats up, the car just shuts off after it gets hot..

i can let it cool down and it will start back up but then shut off again

If you get DTC 16 (low Resolution) and DTC 36 (high resolution) pulse codes, it's prolly the opti

 

Consider replacing the water temp sensor mounted in the water pump. If this sensor is bad, it won't set a code... and it's cheap and easy to replace.

 

Think about the things that weaken when they overheat.... IC Module, Opti optical module, coil, wire insulation, fuel pump. Lots of possibilities.

There are DTC codes for high (short) and low (open circuit) temp failures on the CLT temp sensor. What you can't tell is how accurate the sensor is when its still working. Very easy to check with an ohm meter.

 

I put the car aside for the last few months, but it's time to start getting mod minded and buy some more winter upgrades so I went and got it scanned....

Codes that appeared:

32 (EGR)
42 (Ignition Control Ground Circuit)
44 (Front 02 Sensor)

I drove the car some today after changing the oil and diff fluid and the problem is still current... still a very temperature dependant problem as well.

any help would be AWESOME.

Thanks guys,

John

 

TTT

guys I could really use the help!

Thanks,

John

 

190-200 isn't hot. That's what mine runs. My 1994 Z28 would get up to 225-235. I stuck a 160* tstat and tuned the fans to a lower temp and it's never gotten over 185 since.

 

try changing your 02s first. Mine did the same thing your describing, and I found out my left 02 sensor wire was unplugged

 

That's what mine was doing. I'm changing the opti right now to see if that cures it. I also had a burnt wire that caused a lot of stumbling. It fixed it for a while but the opti started to go.

 

Opti...

 

I've been told in this thread and numerous other times this isn't the opti and the codes aren't opti codes, so... unless you have had an identical experience and it was the opti, please explain your decision to post "opti"

thanks to everyone else, I now have a stepping stone in what I hope is the right direction. I'll be checking the 02's in a few days and my car was supposed to get a tune in it LONG ago so I could put my 160* t-stat in but now I don't think I can run w/ a tune because the cars goal is SCCA Solo F-Stock and I believe a tune bumps me into ESP.... I have to read a little more up on this to be sure.

anyone know what CODE 42 is?

 

I had a very similar problem with my car. It was a bad water pump, coolant was leaking out of the weep hole and after a while making its way into the opti. The after stopping the car and cooling down as I though ( was really drying out). The car would run fine. Maybe your having the same issue. Check for coolant at the weep hole when u 1st shut the car off. Good luck

 

Does the radiator overheat? Does the temp keep going up or does it stay constant at 200 degrees?

Backfiring, bogging, and holding gears sounds like optispark to me.
You are definitely due for one based on the car's year and presumed mileage. The optispark went out on my 95z at 100K miles in 2002 or so. You will know it is your opti if the bogging, etc. gets progressively worse, i.e. 4th then 3rd, 2nd, then 1st. Start by changing the plugs and wires first though.