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I have swapped a 5.3 vortec engine into my '63 Jeep. It starts and idles great, but after about 10 seconds the accelerator pedal is unresponsive. I have confirmed that each 5v reference output at the ECM has 5v. The TPS and Apps 5v reference wires only have 3.7v. If I turn the key to the on position (not running) I can see the throttle plate is responsive to the accelerator pedal, but at WOT it doesn't look to be completely open. I'm pretty sure the issue is not getting 5v to either the TPS or the PPS.
It seems that something is dropping voltage between the ECM and each of the sensors.
I'm trying to figure out where the voltage drop is coming from.....also I don't know which 5v reference pinouts on the ECM feed the TPS and PPS sensors.
Also, I checked each Ground pinout on the ECM for continuity to a good ground on the block and all check out. The engine, body, and frame all have new solid grounding straps to the battery (-).
Are you using a stand alone ECM or the factory computer from GM? In either case, you should access to trouble codes and live data.
Also, volt drop testing while loading the grounds is much better than ohm testing.
I'm using the factory computer that was 're-flashed'. I have pulled these two codes:
P2120 and P2125. One is for Switch D circuit and the other Switch E circuit. I can pull live data, but I don't really know how to interpret it.
It looks like the pedal position sensor and the throttle position sensor get their 5 v reference from the TAC Throttle actuator Control Unit, but I'm only seeing 3.7v coming off that. So, I'm assuming their is something between the ECM and the TAC that is dropping the voltage.
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