Re: 502 MPI problems, help
 

It should be at 100% (or very close) when the throttle plates are fully open. Does it read zero when closed? is there a lag between opening the throttle and the increase of throttle position shown on the scan tool? You may have a bad TPS.

Dave

Re: 502 MPI problems, help
 

I don´t think there is a lag, I´ll have to check. But I noted that it only went to 73%. What are the effects? I saw a diagram in a post that the higher percentage, the leaner mixture. Is that correct? Can it be adjusted?

Re: 502 MPI problems, help
 

If your ECM is only delivering fuel for 73% throttle and the actual throttle position is 100%, you will run lean. That could explain why the plugs are white with (what I beliveve to be) the correct 36PSI regulator, and look better (and not rich) with the 43PSI regulator. The TPS can not be adjusted as far as I know. A new TPS and a swap back to the 36PSI regulator would be my course of action.

Dave

Re: 502 MPI problems, help
 

Dave, do you know if and how the absolute value of the TP Sensor voltage is used to adjust fuel delivery? I know that the MAP value and rpm are used as the main input to determine injector opening times. The absolute value of the TP sensor may be used for some further adjustment. Do you know how?
I found this one in another thread. Maybe it is not relevant?

Re: 502 MPI problems, help
 

I did a tune up this winter and changed plug wires and had a similar problem to yours. I ended up changing the knock sensor, coil, iac motor, ect sensor, mat sensor, fuel pump, regulator and finally decided to change back to my old wires before the problem went away...... I used an after market 8mil wire, maybe the suppression quality wasn't that great? It took me a lot of money and time before I finally figured out what happened.
I ended up going with an Aeromotive pump, filter and regulator and adding a fuel pressure gauge on the regulator and on the dash. I tapped the fule cooler to accept a 10 an fitting, removed the stock regulator and taped a 1/8 pipe thread for a sending unit. So a 50 dollar set of spark plugs wires ended up costing me 2k and a ton of trouble. But my fuel system is the cats ass now........... :eek: :D :cool:

Old thread but you just solved one of my headaches today! thanks!