Help Tracing Fuel Problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Low69CST · 03-07-2020, 10:16 PM

Have a 87 half ton, 4x4, 350, and dual tanks. Before and after restoring the truck it had a periodic issue running on the auxiliary tank, which turned into an occasional problem running and getting a gas gauge reading. And now it just won't run or get a fuel level reading from either tank.

I got a new switch for the dash. Testing the wires I found the tan/white (#120) to be dead. I expected it to be hot. Thinking this was the issue I made a hot jumper and ground jumper for the tan and gray wires (#920 & #921). This did make the fuel gauge work, but the truck wouldn't run.

Thinking the tan/white (#120) being dead as the problem I traced the wire to the fuel relay on the firewall. I bought a new relay, which didn't fix the problem. Then began checking the wires in the plug for the relay with a test light. None of those wires were hot with they key on or while cranking. There should be some hot wires like the orange (#440) from the battery and the dark green/white (#465). It doesn't make sense to me that all these wires should be dead.

Any advice from anyone? The diagrahm shows a fuse on the orange wire (#440). Does anyone know where that is? I haven't seen it. Thanks.

**hatzie** · 03-09-2020, 05:09 PM

It's the ECM B fuse in the cab.

03-09-2020, 05:09 PM	#2
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: Help Tracing Fuel Problem It's the ECM B fuse in the cab. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

03-07-2020, 10:16 PM	#1
Low69CST Registered User Join Date: May 2000 Location: Frankfort, Kentucky, USA Posts: 2,163	Help Tracing Fuel Problem Have a 87 half ton, 4x4, 350, and dual tanks. Before and after restoring the truck it had a periodic issue running on the auxiliary tank, which turned into an occasional problem running and getting a gas gauge reading. And now it just won't run or get a fuel level reading from either tank. I got a new switch for the dash. Testing the wires I found the tan/white (#120) to be dead. I expected it to be hot. Thinking this was the issue I made a hot jumper and ground jumper for the tan and gray wires (#920 & #921). This did make the fuel gauge work, but the truck wouldn't run. Thinking the tan/white (#120) being dead as the problem I traced the wire to the fuel relay on the firewall. I bought a new relay, which didn't fix the problem. Then began checking the wires in the plug for the relay with a test light. None of those wires were hot with they key on or while cranking. There should be some hot wires like the orange (#440) from the battery and the dark green/white (#465). It doesn't make sense to me that all these wires should be dead. Any advice from anyone? The diagrahm shows a fuse on the orange wire (#440). Does anyone know where that is? I haven't seen it. Thanks. Attached Images __________________ '69 CST Short fleetside Lowered, 400 small block, 700R4, 4 wheel disc brakes, front sway bar & rear camaro sway bar (in progress) '87 V10 4x4 Short Fleetside Quad Suspension and Dual Tanks



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