Check engine light and no self test...WTF?

[southbronx]

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.

 

[BlackFox5.0]

Are you sure you jumpered the plugs properly?

 

[autoXr1]

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.

http://www.stangtuning.com/showthread.php?t=1656

 

[southbronx]

Grounding did the trick

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.

 

[jb89coupe]

Is the CEL on all the time?

 

[southbronx]

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.