I have been trying to diagnose this problem for a while now. I try and start the car, it cranks, i get fuel pressure but im not getting spark. When we disconnect the wire from the pcm that goes to the throttle position sensor it starts. But runs rough because the TPS isnt working. But when its all hooked up it wont start at all. I tried replacing the sensor but still nothing. Any ideas? Do i have some wiring messed up?

I have a 98 camaro that had a 3.8 V6 and a 5 speed. We swapped in a 94 LT1 with auto and a OBD2 pcm custom programmed to work. I get the same results with the 94 pcm and the OBD2 pcm.

Please help.

 

Any time you have a sensor that appears to be bad, you should check the wires for the correct voltages, grounds and continuity. BEFORE you go replacing the sensor. You should also understand what is connected to the circuit you are dealing with. For example, some sensors have a common supply voltage line that provides +voltage to more than one sensor. If one sensor is shorted internally to ground lets say, all the sensors on that same +voltage line will appear bad.

In your case, we don't have a clue what is causing your problem. But the TPS is a good place to start. I would suggest you stick to troubleshooting the engine problem with the 94 (OBDI) PCM since the 98 OBDII was used for many things your older engine does not have and who knows what might have been incorrectly programmed on the OBDII PCM.

Next, understanding the TPS circuit will help and there are 3 sensors that have a common ground. The TPS, the coolant temp sensor ECT(not the one for the gage) and the trans fluid temp sensor TFT. I would suggest you check the wiring at all 3 sensors to the PCM to be sure they are correctly hooked up. Start with the TPS. Check that the grey wire has +5v and the black wire is a ground reference. Should measure 5v between the grey and the black wire. If that is the good, move the throttle and be sure the dark blue wire has a voltage swing of about .5 to 5 volts when you move the throttle. You measure this between the black and the dark blue wire. Now be sure the 3 wires go to the PCM on the following pins. Sensor output goes to the white PCM connector pin 22(dark blue wire). 5 volts comes from the black PCM connector pin 28 (grey wire) and reference comes from the black PCM connector pin 6 on the black wire. This black wire will also go to the ECT and the TFT as I noted above.

If anyone of the sensors it not working correctly, try unplugging one of the other sensors, or both to see if the one your working on starts to work properly.

Hope that helps. Let us know how we can help you further.
Dave

 

Hmm, thats some good info. Thank you. I will try that tommorow and see if anything works. I'll keep you updated, hopefully we can figure it out.