posted this in electronics way back when with really no informative response, but maybe someone here that knows ECM's and their circuitry might be able to help... the vehicle i'm referring to is my '91 5.7L TPI.

problem = with key in the "ON" position, fuel pump cycles for 2 seconds like it's supposed to. if i pull the headlight switch, or hit the brakes, fuel pump will cycle again like it's NOT supposed to. this gremlin was discovered after a rebuild almost a year ago, but have been doing other things to the car in the meantime. the only info i can add to the troubleshooting is that if i disconnect either connector on the (remote) coil, it will not do it. so i supplied power direct from battery to coil for it's power supply, and it still did it. i have also replaced the ignition module and pick-up coil in the distributor, both to no avail. i understand the fuel pump is powered by the ecm when it receives the signal from the dist, and is also wired to the oil pressure switch. i'm not clear as to which way the current flows on any of it, but have a digital VOM to chase wires with. i just don't want to chase my tail with this. it really isn't much of a problem, but it isn't right that it is doing it, besides being annoying. i don't know where the ECM could be getting another input signal from to cycle the pump...

 

99% sure that the ECM is seeing a DRP when it is not supposed to. This is what is kicking the pump back on. I would start by checking the grounds between the ECM and engine, then the grounds between the battery, chassis, and engine.

The ECM should only be grounded to the engine. There are several grounds on the back of both cylinder heads.

The forward lamp harness has some grounds attached to the radiator support, passenger side. Check the ground between the battery negative terminal and the chassis.

If all those check out then it may be the ref-low wire between the distributor and the ECM. This is the blk/red wire on terminal A of the distributor 4 wire connector, to D9 on the ECM.

RBob.

 

a little more playing around with it yesterday and now it doesn't cycle with the brakes, but will with the back-up lights. according to my diagrams, the light switch and the reverse lights are on cicuit #150, ecm is on #450, and a common connection point is the back of the pass head at G118. those grounds were repaired but i think the stud itself on the back of the head may be a problem, so gonna start there with it. easy enough to get to, but not as easy as the other head... once i disconnect it, i'll check the wiring for continuity. gonna check out the ref low wire, too. i'll post with results, and hopefully will have them today or tomorrow.

 

RBob, disconnected the grounds from G118 and attached (jumpered) them directly to the battery neg post. still got the pump w/lights. checked those same wires to the connector at the ecm (D7 and A12), got .2 ohm. checked all wires for ignition module to ecm (D7,D8,C7,C8) and all read about .2 ohm also. i was sure i had checked these way back when, but easy enough to check again. continuity for ground seems to be good from battery through the block. i didn't check G112 again (but will) cuz i had a problem there before and had to clean that all up. i realize the ecm is grounded there also, but the symptoms i had with that ground before appear to be corrected now. one last note is that when i check my DVM leads, i get .2 ohm there, as well, so all the readings i get seem to be "solid". any more ideas or direction? i'm heading back out to clean the actual body parts where the light grounds go to, but they also didn't seem to yield any problems when i jumpered those, either...

KAM

 

If you have a pin extraction tool, remove the pins at the ECM connector from the HEI module. I believe they are BD8 and BD9, a purple/white and black/red wire, respectively. If the fuel pump still runs with the aplication of the backup lamps, brake, or whatever other device(s) caused the gremlins, the problem is not likely induced by the HEI REF or REF signals. If this is the case, you may want to monitor input power to the ECM during the application of these external devices.

If the pump does NOT run in this configuration, the problem is likely as RBob suggests, and you'll need to dig into the harness and grounding further.

 

the fuel pump (apparently) is shorted to ground... i was able to isolate everything today and finally figure it out, but that's the deal... one thing that really sucks about it, is that the tank is FULL... anyhow, it was causing power to ground, but won't be for long.