Hello I have a 1994 z28 that is giving me some weird problems and before I start replacing stuff I wanted your opinions.

When I start the car in the morning it starts up great and runs good, But has a code set for ignition control module shorted or grounded. After about 10 minutes the light goes off and no codes are present(passed smog this way). But recently around the time the light goes out it starts to miss really bad and pings under moderate acceleration. Then when I shut it off and restart it it cranks really slowly as if the timing is way to far advanced. when I disconnect the coil it cranks normally.

The opti, cap, and rotor are all auto zone pieces with 1500miles. same with plugs and wires.

So what do you guys think? If I am gonna replace my opti again I am going with gm parts.
I dont know about the code because problems dont start untill the light goes out.

so please help me out, will

 

First do more investigation before shot gunning parts. If you think about your problem occuring after it warms up, it's likely not the opti. Of the 2 sections of the opti, only the low voltage (feedback) portion of it could have a warm problem. Both the hi and low res signals would be easily viewed for defects.

It's far more likely you have a control problem once the engine goes into closed loop. If you included information that you have headers(?), I would say you had a wiring issue to one of the O2's. You can do a simple test to see if you do indeed have a closed loop control problem by unplugging one of the O2s and drive it around. If it drives close to normal unplugged, you know the issue.

The next step would be to view the O2 signals with the O2 unplugged and then with the 2 signal wires shorted to ground. That will tell you if the wires are intact and if the PCM is seeing them correctly.

 

Everything is stock on my motor. I will try to see if the O2 sensors are working It doesnt smell rich but initially I thought it was a fuel prob but after pressure tests and replacing filter I ruled that out.

thanks for any help, will

 

What makes you think an O2 problem is only rich????????

What if the signal appeared to the PCM as if it were rich??? Would it not try pull fuel?

This is the exact problem I had. The right O2 signal was residing above center voltage all the time. The PCM kept pulling fuel until it ran so bad, it would jump back to open loop. Clear itself and go back to closed loop only to start the whole process all over again. The problem turned out to be cooked wires in the trunk line going down the inner right fender from top to bottom.

The way I found the problem after scanning it and seeing where the O2 signal was most of the time. Was to short the 2 signal lines to the ground line and saw that the PCM showed it was still higher than center voltage instead of lower. At that point I knew the wiring was bad and sinply looked in the first obvious place for what turned out to be the "cooked" area.
You got to learn how to think outside of the box.

 

I just didnt think it is fuel because of the hard starting when it gets warm. I will definately try to get my hands on a scanner to monitor the o2 sensors and look for a change when I short the wires at the o2.

Another thing that is throwing me off is the code I get for the Ignition Control module shorted or grounded. then going away.

thanks, will