My 1994 suburban will start and run for 10-30 min. after sitting and cold. While running the fuel pump relay and the oil pressure switch both check out. Then the truck suddenly stops with no more fuel delivery. When in this no start condition no gas flows from the injectors, no power in the grey fuel pump wire, power at the injectors, power to the fuel pump relay orange wire, engine will run if fuel poured into TB. I can jump the pump and it turns on. Fuel is present at the injectors and has good flow and pressure (9-14 psi). The Mil does not light to check any trouble codes. The ECM seems to reset after a considerable length of time (hours) and the Mil comes back on with no trouble codes and truck starts and runs. Also a clicking has been heard just before the the Mil goes out for good. Could this be a power fuse/relay for the ecm or one of its circuits? If so, where are they located and what specs do I need to check/test them? Is my ECM ok?
I checked all of the fuseable links and they were all good. Next I decided to check all the power wires to the ECM and also the grounds from a wiring diagram because the Mil is controlled by the ecm and the bulb was good. The ecm is located behind the glove box. Bingo, the orange wire was only reading 3-5 volts at the ECM, but 12.5 volts after the fuseable link at the underhood fuse block (passenger side firewall). I ran a temp wire directly from after the fuseable link to the orange wire at the ecm and the ecm turned back on and the Mil or "check engine soon" light came on too. The truck started up and has never run smoother.
Note that at first the truck just stalled out and I could restart it right away with no error codes. Eventually the stalling became more frequent with longer reset times required. Once it threw a "code 54" and I thought it was fuel related as each time the gas stopped and I could still start the truck with gas poured into the TB. Ignition ok. My fuel pump turned on and ran if I tested it. I even checked the pressure regulator and the fuel filter to no avail.The orange wire that powers up the ecm is technically part or the fuel pump relay circuit as it also feeds the fuel pump relay 12.5 volts all the time. The thin orange wire from the fuse block is joined to two other thin orange wires in the large group of wires that heads to the ecm along the firewall behind the engine. I had to dig it out of the many wires to find it and remove a lot of tape. It is amazing to me that this one little orange wire could cause so much grief and be so hard to track down. I could not have afforded to take this problem to the Dealer.
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Relay has power, where is the ECM?
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