Good day,

Working on a 1996 F250 with a 460 that runs terrible. It has been running very rich, hard to start and had fouled plugs. I replaced the plugs along with the distributor because at first it appeared that it was just missing really bad.

It is a holdover of the OBD1 system and has flashed codes for the MAP Sensor and TPS low Voltage. I plugged in a known good MAP Sensor and it didn't help any. Then I went to check the voltage at the TPS and was surprised to see that it had no 5V Reference, therefore no Signal voltage either. Ground was good. I did a continuity test back to the ECM and the wiring is good.

My guess is that the ECM has failed but I wanted to run it buy everyone on here before I find a replacement. BTW, I am checking Voltage with KOEO. Thanks

 

It looks like you did everything to verify VREF is not leaving then PCM (computer). I am surprised you did not get codes for the ECT and ACT as well. All of those sensors use VREF.

Just to make sure I would check to see if VREF is getting to those sensors before throwing in a new computer.

 

Was that Pin #26 that you back probed on the Computer Connector?

 

Got it figured out. VREF is used for the EGR, TPS and MAP on this truck according to ALL Data. I forget what pin it was but I actually had two issues going on. I had a dead end in the circuit somewhere between a factory splice on the VREF. Instead of taking the whole harness apart I just built a new lead from the computer to each sensor and had continuity from ECM Connector to all sensors.

Started the truck and it ran great for about 15 seconds then it started acting up again. I checked the VREF and I was only getting .5 volts. I back probed from the ECM connector and again was only getting .5 volts. At this point thought it had to be a bad ECM still. Pulled to ECM to get the numbers on it and decided i would check the female pin on the ECM connector. It looked fine, I had continuity from it to all sensors. But I decided to plug it back in and try and wiggle the connector while measuring VREF at the TPS. It bounced all over the place. I pulled the connector off again and took it apart. I crimped the female terminal down and bit and plugged it back in. 5 volts, passed a 5 minute wiggle test. Truck runs fine now.

I guess the male pin from the ECM wasn't making solid contact with the female pin on the connector to the harness. After squeezing it down a bit it made the fix. Thanks for the help!

 

Glad to see you found the root cause AND replied back.

 

Hopefully it helps somebody down the road.

 

Yes it will. A great example of troubleshooting the problem instead of tossing parts at it.