I have a 1992 4.9 liter that will start and run, but loop will not close and runs rich and lays over when pedal is pushed past 1/4. Scanner shows many codes and will not run KOER test. Could this be a grounding problem? Truck ran fine until it sat for a couple of months.

 

It's not a bad idea to go through and clean up all your grounds, and also go through all the connections for the sensors and make sure they are clean and seal up properly. Use dielectric grease on them, too. I had to chase a bunch of gremlins stemming from corroded connections and ones that would get a lot of moisture in them. I'd do those things before trying to replace stuff that might actually be fine.

 

Thanks, I'm going to check the ground for the computer and the reference voltage. There is a DTC 513 as well as 17 other codes that come up under the KOEO test.

 

OK, maybe I have this figured out. Computer is located directly below windshield. Windshield has been leaking for sometime, so I pulled the computer out of the firewall and found signs of water damage on the outside. Opened the case and found two capacitors and one diode with heat damage and corrosion. I would post a picture, but I'm not sure how to. Hopefully a new ECM and windshield will fix this. I'll post the fix, if this is in fact the whole problem.