Ok guys, I need your help. I have a 94 z28 that develops a missing and backfire thru the exhaust around 20 minutes after driving it. It has been doing this ever since I purchase the car two months ago. I have put it on the scanner again saturday, and it gave us no codes. We watched all the sensors and they are in good working order. We have even put the node on the injectors and they were working properly

This is what I replaced so far:
fuel pump, filter
plugs and wires
opti spark
coil and ignition module

give me so help guys!

I have stump three mechanics.

 

I am guessing O2 sensors.Sounds like its running rich.It should lean out a bit after warming up.

 

I put the car on the scanner, the 02 sensors are working properly. There are no codes showing.

 

mine was doing that to untill I replaced the Opti fixed it right up but since you have already done that has to be a IAT IAC MAF OR O2 sensor.

 

I know these are abbreviations but let me act dumb for a minute. what is the IAT or IAC?????? I know what the maf is. I have changed the coolant temp sensor also. Thanks guys

 

I know that most of what you guys are suggesting are sensors, but would not some of these sensors show up on a diagnostic check. That is the problem that I am having. I am throwing parts on the car, and it is not making a difference.