Allright this is my problem that has been riddling me all weekend. I have a 94 z28 that does not wont to run right. THis is the deal last week i done a rear end swap after it had been on jackstands for about a month, when i went to drive it it would not run well after the thermostat kicked in. It gets to a certain temp then does not wont to run well. If it is cold it will run the best you could ask for doesnt miss idles perfect revs great. When it idles or runs for bout 5-10 mins or gets to that magic temp it starts to backfire and will soon die. It will not fire back up till it cools a lil bit then fire right back up and runs till its hot agian. These are the things ive checked/replaced. Coil, ignition module, water temp sensor(on the water pump), mass airs, took off and cleaned the opti (which was completly dry), fuel pressure is 41 at idle 37 while off with the key on and never changes while running, fuel filter, checked and double checked the grounds and wiring. The other funny thing that happens is the tack works then goes haywire when the car does. Im puzzled, how could it go from running excelent to messin up after a rear end install? Could it be the Opti? What else could it be? This has stumped me and about 4 other ppl. Oh and it isnt setting any codes. I need help PLEASE. Thanks
Zach

 

Sounds like the problem occurs when the PCM kicks into closed loop. Have you checked for any codes? Scanned it? Checked the O2 sensors?

 

I havent got my scanner access yet and the car is not mobile, how else would i check the o2's? i did unplug them, but got no change. Besides replacing the 02's and scanning it how would i check to see if thats goin on? I mean if its the o2s great then i wont have to change the opti which is my next move. what should i do next? Go ahead and spend the 100 bux for the 02's or??

Thanks again.

 

before i spent any money i would have it scanned and see what the O2"s are doing. Your problym does look like its occuring when its in closed loop.

 

My car did the exact same thing. I changed the plugs and wires, it did wonders for me

 

if you havent replaced, just checked, the module i'd check there, also could be the crank sensor inside of opti in that year, i'd really lean towards module though

 

The ignition module was replaced with a new one. I was thinking the module inside the opti as well. but like injuneer said it does sound like it dies when it changes loops.

 

UPDATE:

Well it will not run at all now, i guess the opti has jus bit the dust. I did pull the o2s and had a look and wow they were solid black and really think carbon. I still havent got it scanned yet but it still hasnt set any codes. Im gonna try to get a scanner down here soon.