1987 V10 with carb and dual tanks will not stay running

[Shoote]

Still struggling with no fuel after initial start up. I jumped the wires that went to the factory oil pressure sending unit and the fuel pumps did not turn on. There is power when I jumped those two wires though. If I have power at the fuel selector valve mounted on the frame rail near the tanks......could it be bad? I replaced it less than 1.000 miles ago with the Delco part, I know that does not mean much the way parts are now. If not the tank selector valve what else could it be?
Fuel pressure regulator is adjusted to run at 6 to 7 psi.

 

[Ricko1966]

Check for power at the O.P switch key on engine off. Which terminal has power?

 

[Shoote]

The last 1.5 years I could hear the fuel pump turn on as soon as I turned the key to start.

I bought a Powe Probe so I have more information.
Fuel relay on firewall
Orange wire 12.5v
Ground wire is good
Tan/white wire 12.5
Green/white wire 12.4

Factory oil pressure switch wires 12.5 each when connected with fused wire connector

Factory plug going into fuel selector valve

Gray wire- fuel tank selector wire working. Does not stop working unless I release the switch in the cab. I can hear my 85 truck slow down then I release the switch in the cab. May not make any difference.
Tan wire- drivers side fuel pump works with power probe giving power

Tan/white wire- no power, nothing happens when I add power from the power probe
Pink/black wire- no power nothing happens when I add power from the power probe
Pink wire- has power with key on

I hope one of you knows what is wrong. Next step is a tow to a shop. Hate the thought of that.

 

[Ricko1966]

The last 1.5 years I could hear the fuel pump turn on as soon as I turned the key to start.

I bought a Powe Probe so I have more information.
Fuel relay on firewall
Orange wire 12.5v
Ground wire is good
Tan/white wire 12.5
Green/white wire 12.4

Factory oil pressure switch wires 12.5 each when connected with fused wire connector

Factory plug going into fuel selector valve

Gray wire- fuel tank selector wire working. Does not stop working unless I release the switch in the cab. I can hear my 85 truck slow down then I release the switch in the cab. May not make any difference.
Tan wire- drivers side fuel pump works with power probe giving power

Tan/white wire- no power, nothing happens when I add power from the power probe
Pink/black wire- no power nothing happens when I add power from the power probe
Pink wire- has power with key on

I hope one of you knows what is wrong. Next step is a tow to a shop. Hate the thought of that.

Take the fused connector out and tell me which term8nal is hot

 

[Shoote]

Ignition on:
Orange is hot
Tan/white is hot

Ignition off:
Orange is hot
Tan/white is not hot

 

[Ricko1966]

I've got some more info for you found a better schematic for the relay,trying to help another member. With that schematic I can see all inputs and outputs to and from the relay.

 

[Ricko1966]

Ignition on:
Orange is hot
Tan/white is hot

Ignition off:
Orange is hot
Tan/white is not hot

Oh wow this complicates things,so with no jumper and ignition on the tan white has power? If so you need to check for power in and out of the fuel tank selector switch. You have power for the pump,it's just not making it to the pump. Posted previous post before I saw your post.

 

[Ricko1966]

Looks like the tan and white feeds power to the selector switch comes out on 2 wires a grey and a tan. Grey for right tank tan for left.

 

[Shoote]

With the key on I have power to the tank selector switch through the tan/white wire. When I depress the switch to the left tank I get power to the tan wire. It does not stay hot, only when I depress the switch. When I let up on the switch the power stops. The gray wire for the passenger side tank does the same thing. Should the wire to the dri ers tank stay hot when the selector is on the left tank?

 

[Ricko1966]

With the key on I have power to the tank selector switch through the tan/white wire. When I depress the switch to the left tank I get power to the tan wire. It does not stay hot, only when I depress the switch. When I let up on the switch the power stops. The gray wire for the passenger side tank does the same thing. Should the wire to the dri ers tank stay hot when the selector is on the left tank?

Are checking power in and out,at the switch? If so sounds like the switch is failing try jumping around it.

 

[Shoote]

It does switch from tank to tank and it is a new switch, but I know that doesn't mean it's good. I will bypass and see what happens. Thank you.

 

[Ricko1966]

With the key on I have power to the tank selector switch through the tan/white wire. When I depress the switch to the left tank I get power to the tan wire. It does not stay hot, only when I depress the switch. When I let up on the switch the power stops. The gray wire for the passenger side tank does the same thing. Should the wire to the dri ers tank stay hot when the selector is on the left tank?

Drivers and left are the same.

 

[GTGT]

Just a thought. Has the tank selector valve been replaced? If so, it sounds as if an old style solenoid operated valve may have been used. This is what the symptoms sound like. The newer style valves are motor operated, not solenoid operated. The solenoid valve uses a reversing two position switch that stays on to keep the solenoid in position. The motor operated valve uses a reversing momentary switch. I realize this does not allow for the wash down, but this is what the symptoms sound like. I had a 79 GMC with factory duals with the solenoid valve. I am currently working on on 85 GMC and have added the second tank which requires the motor driven valve. Again, just a thought.

 

[Shoote]

About one year ago I replaced the solenoid valve because it was leaking fuel. I used the valve in the picture. Not sure if it is the old or new style.

 

[AuroraGirl]

About one year ago I replaced the solenoid valve because it was leaking fuel. I used the valve in the picture. Not sure if it is the old or new style.

new