Anyone come across a 5.0 that would not do any of the self tests (KOEO/KOER)? I got a check engine light and tried pulling the codes with no luck. I've traced the wires for any faults and have come up dry. Still runs though.
Insufficient grounding? Try taking a piece of 12-16ga stranded wire...stick one end into the small gray connector where you plug in your scanner...connect the other end to a good chassis ground or negative battery post. You should be able to run the self-tests.
Apart from not being able to run self-tests with a scanner, insufficient grounding can create all sorts of little tuning issues due to electrical "noise" and excessive voltage drop.
Thanks autoXr1. Your advice did the trick. I've had Mustangs for 14 years (this one for 10) and have done all of my own work: upgrades, electrical, diagnoses, etc... but this was a first. I guess going to an upgraded 4 gauge alternator cable so the 130 amp alternator can push the juice must have been too much for the chasis to handle. I went ahead and swapped out for a heavier gauge grounding cable and cleaned up all of the 4-5 grounding points in the car. Thanks again. Semper Fi.
No. The CEL went off as soon as I cleaned up the grounding points around the car, specifically the one near the computer. I also swapped out the negative cable for a heavier gauge (4 ga) and cleaned up the contact on the block. I had a 130-amp alt for a while and u/g the main cable just recently.