Hi just wondering, I have a 94 k2500 with a 6.5, when you do the ECM test is it normal for the throttle service soon light to come on as well? Furthermore can the throttle position sensor affect the transmission shifting into reverse? finally if i unplug the TPS the accelerator pedal will still rev the engine in park and drive but in reverse it is completely dead is this normal?

Just to clarify I meant Service Throttle soon...

I think it's your reverse sprag, having just lost R myself. The APP pedal is three potentiometers with 5v of reference signal on each. The first should read .5v the second 4.0v and the third 4.5 v. if any of the three signals increase instead of decrease it's a voltage spike that can make the engne race at times, like when you drop it into R from D.

What is the ECM test you are referring to?

If any one of the three controls in the '94 APP sensor are defective, PCM will log a DTC, but vehicle will still operate on the remaining two, with a STS indication.

HOWEVER - and that is a mighty big however - since the '94 PCM controls the engine via the APP input, it would be sheer magic for the PCM to respond to an unplugged APP, with no input of any control voltages to the PCM.

The '91-93, however, with mechanical fuel injection, would have the TPS on the Inj Pump throttle shaft, and the throttle cable would control engine output with TPS connector removed.

TPS output range is dependent on throttle shaft rotation - any restricted rotation reduces TPS function, and engine output.

Not sure how the Transmission Control Module TCM would interface with the mech Inj Pump to restrict engine output in Reverse, as only IP electrical control is HPCA solenoid and Fuel Shutoff Solenoid, with external Fast Idle solenoid .

His truck is a '94 F?

I just realized what you were saying, I am going to have to check that out again, with no sensor output and no throttle cable how could it possibly work at all unplugged. Gotta go check it out!