2000 f250 7.3 power stroke short to ground on v ref line. Just replaced all my injectors to fix a misfire issue, but it's still running rough and occasionally stalls and surges at idle (misfire appears to be fixed though). Stumbled across my v ref short to ground trying to track down the issue. Also discovered no communication to OBD port which started after I shorted my alternator to ground because I hadn't disconnected my battery like a dingus.



Reading 250 ohms on v ref line to CPS, EBP, ICP, MAP, and APS sensors. Still reading 5 volts to all sensors with key on though, so maybe I don't need to be concerned? Short disappears when I disconnect PCM. This suggests to me that the short is local to the PCM. I sent in PCM for testing, and they said it passed all their tests. I know there is a barometric pressure sensor internal to PCMs for this year range, and that is the only other sensor connected to the v ref line as far as I'm aware. Could that sensor be causing my issue? Are my above conclusions correct, or is there something else I should be looking at?



Unsure if related but I also have no communication to my OBD port. Power to OBD port, power to cigarette lighter. Port was communicating before, like I said I did accidentally short across my alternator post but have found no blown fuses or relays.



Both issues point me to bad PCM, but it supposedly tested good so I'm wondering if I could be missing anything else. Thanks in advance!

 

Have you checked the fusible links on the passenger fender well? There should be one between the alternator and battery and another on the main power wire from the starter solenoid back around the firewall. I'm not sure that they could be the source of your reference voltage problems but if you shorted the batteries or alternator one or both should have blown before any damage was done

Edit: Who did you have test the PCM? Baro should have been part of their test procedure considering it's integrated with the PCM. Also how are you verifying fuses are good, visual inspection or resistance test with a multimeter? If you're not getting power to the OBD port or the power port then I would probably just change that fuse regardless of visual or meter readings.

 

I have not checked those fusible links, thank you! I betcha one of those is blown, I wonder if that'd somehow cause an issue with the OBD communication?

And for the fuses I've been checking continuity and voltage with a multimeter.

 

I couldn't say for sure because electrical isn't my strongest area, but a possibility I could imagine causing all kinds of strangeness would be just a shoestring connection. Where the link blew but just a thread or two of the wire is still making contact. So basically you would read 12v or whatever but have no load carrying capability. It would likely show high resistance too. It would be like trying to run your house all from just one of those super cheap little indoor extension cords that are good for a lamp and a phone charger and that's it.