Fuel System Issues

[txfour]

1987 GMC SWB.

Symptoms -

1 - Fuel Gauge stuck at 1/4 tank. Disconnected grounds on frame and had no impact on gauge. Disconnected selector valve at frame and gauge goes past full. Reconnect it and gauge goes back to 1/4 full.

2- Selector switch not working.

Tried Fixes -

2 Brand New Tanks
2 Brand New Sending Units
1 Brand New Selector Switch in Dash
1 Brand new Selector Valve
2 Sanded Grounds On Top of Frame

Where the heck is the fuse for this bad boy. I have located the fuse block, but find nothing that seems to refer to fuel selctor valve.

 

[MadOgre]

@chengny

 

[chengny]

1987 is a hard year to research. That was the crossover year from carbureted fuel systems to the TBI system.

TBI fuel system? I checked your prior posts and noticed that you had purchased an engine from a 1994 and were intending to install it. Did that ever happen?

The fuel tank switching circuitry associated with a TBI system is very different than what is used with a mechanical fuel pump.

With a mechanical pump/carb system - when the tanks are switched (on the dash) only the plumbing and level sensing are changed.

With a TBI system - not only are the plumbing and level sensing re-aligned, but also the power to the electric fuel pumps is switched to the on-line tank.

Was the truck originally equipped with a mechanical pump/carburetor?

Where the heck is the fuse for this bad boy. I have located the fuse block, but find nothing that seems to refer to fuel selctor valve.

The tank switch system doesn't have a dedicated fuse. It is an add-on option, and - like other options - it's power lead is a plug-in type. The power for the auxiliary tank switching circuit is supplied on the IGNITION bank - and may be plugged into any of those sockets (pink wire). That bank is protected by the 20A fuse in the slot labeled IGNITION:

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