thunderstick

for my '91, i believe the ecm is a 7730... anyways, i need to verify if pin "D1" is supposed to be a ground. (blk/wht wire) i've been chasing a gremlin for a while, and decided to try reading at the ecm (since it is cycling the fuel pump with the lights, key on). i know the black/white wires are grounds, but don't know if all of them are. this one reads .06 V with key off, 9.07 V with key on, then jumps to about 9.7+ V if i hit the lights. i can chase the wire down, but if anyone can verify that wire for me, i'd appreciate it... i'm going to go try to locate it under the hood in the meantime... thanks.

KAM

Trickster

On a V8 TBI, pin "D1" is a ground wire to the ECM with a splice going to pin "A12" of the ECM. This ground goes to the engine ground on the right cylinder head and pin "A" of the ALDL. It would be a black/white wire.
On a 3.1L V6 engine it is a system ground to the back of the right cylinder head with a return wire (tan) going back to pin "E15" of the ECM for O2 sensor ground.
On the 5.0L & 5.7L TPI V8 engines it is a ground going to the right cylinder head and pin "A" of the ALDL and is a black/white wire.

thunderstick

thanks, trickster. you probably remember this one from last weekend... still working on it. but i have made another discovery. in addition to that D1 pin having 9+ volts when power is applied, so does the ground on the a/c pressure switch, and (drumroll, please) so does the fuel pump relay ground. imagine that. one of the grounds on the back of the head is also showing the voltage, but not the one with the tan wire. it is one with two of the blk/wht wires. right now i'm pulling up the wire bundle and physically tracing the wires down to a common joint, but that'll probably take me back somewhere else... anyways, the voltage shows at all points mentioned with them all disconnected tfrom their respective component. man, this really sucks...

KAM

thunderstick

ok - i pulled up the wire bundle(s) with the suspect "hot" grounds and narrowed it down to one of the wires going in to the car (ugh!) it was attached to the lug at the back of the head, so i traced all wires attached going both directions, and unfortunately, two of them go into the cabin... so i decided to isolate it if possible, and cut one of the two wires attached to the lug, and that isolated it somewhat. both of the wires in question go thru that big connector looking thing at the firewall. both of the wires read 0 volts with the key off, but with key on, one reads 9+ volts, the other 5+ volts. IF the ecm is all connected, that same wire will read less than 1 volt, but still has a trace. tomorrow i'm going to try again to isolate the source by pulling fuses one at a time, but that didn't seem to work today. any help will be appreciated... thanks.

KAM