Finally got my race LT headers installed with 160 t-stat. The PCM was also tuned fully with lower fan temps etc.

Problems:

1. Cooling fans not coming on. We put power to each fan and they worked. We checked the relays and they worked. We followed the troubleshooting guide in my Chilton book for fans not working and found that 2 out of 3 relays were not getting power correctly from the PCM. So is this a PCM problem??


2. PCM still throws a misfire code. Before we changed plug/wires the PCM threw a misfire code and the motor acted like it was misfiring. After we fired it up with the tuned PCM it still throws a misfire code when the motor does not appear to be misfiring. What do you boys think?

 

Nobody????

 

Have you checked the wire harness on the pass side? It runs up the inside of the body, right next to the header. A buddy of mine installed Mac mid length headers, and started having strange electrical issues. Turns out this harness was damaged from the heat produced by the headers.

He had to lengthen each wire in the harness and reroute it away from the header.

One of the wires in the harness goes to the crank position sensor. This sensor is used by the PCM to detect misfires. Not sure if the fan relay power wires are loced here though

Good luck!
Thomas.

 

Thanks for the reply Stoopalini.

I'll check that area when I get the car back from the exhaust shop. So a bad crank position sensor can cause a misfire reading?

 

Yes, because the PCM uses the signal from the CPS to determine if a misfire is happening. If the sensor, or the wire to the sensor is having problems, it can cause the PCM to think there is a misfire.

Thomas.