dual fuel tank and only one wants to play

[tex_waco_usmc]

As the title states... 86 GMC with 87 tanks and drivetrain (350 TBI with 700R4). Drivers side tank and sending unit are brand new and work perfectly. Passenger side got a cleaning (as best I could) and new pump. Worked good at first except the sending unit reads right when it feels like it. Now it wont even idle for long when running on the passenger side tank. She always starts right back up but wont idle. If you are driving and have to let off to brake and/or coast she dies. This only happens when running on the passenger side tank.

So confused. Any help would be greatly appreciated.

[DBLSPRT68]

Your transfer valve seems to be bad. I had a dual tank truck for 10 years, and had trouble with this once. It'll run fine off the primary tank (your drivers side tank), soon as you switch over and the fuel runs through the line, sputter= die. Have someone activate the switch, while your under the truck (battery switched on but not running), and hold the valve to feel/hear if it moves. They are expensive new, but post on classifieds about wanting a nice used one. Also, the switch on my old truck; you would have to make sure it's fully actuated to the new position with some pressure. Don't just gently click over, click and push. Let us know what you find out. David

[tex_waco_usmc]

I was leaning towards that, but of the valve was bad why will it fire back up after it dies?
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[DBLSPRT68]

Not sure..... It might be because the drivers side tank is primary, and it reverts to it on start up??? It's going to take some troubleshooting on your part. I know when this happened to me, it drove me crazy for a while... Good luck. I hope some others will chime in.

[wilkin250r]

I had similar symptoms on a single-tank truck a while back, turned out to be a rotted section of hose that wouldn't allow enough fuel flow. It let a little through, so if it sat for several minutes the line would fill up with fuel, but as soon as you started running it would drain the fuel from the line and couldn't pull enough through the bad section to keep running.

[wilkin250r]

86/87 with the TBI is going to have in-tank pumps, correct? I know the pump is new, but it's still my first suspect. I would hook up a fuel pressure guage and test it.

[tex_waco_usmc]

Originally Posted by wilkin250r

I had similar symptoms on a single-tank truck a while back, turned out to be a rotted section of hose that wouldn't allow enough fuel flow. It let a little through, so if it sat for several minutes the line would fill up with fuel, but as soon as you started running it would drain the fuel from the line and couldn't pull enough through the bad section to keep running.

Hoses are new too
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[tex_waco_usmc]

Originally Posted by wilkin250r

86/87 with the TBI is going to have in-tank pumps, correct? I know the pump is new, but it's still my first suspect. I would hook up a fuel pressure guage and test it.

When I get home from this business trip in Des Moines I'm going to check fuel pressure
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[KrazyRay]

You could be the victim of a bad in tank fuel hose. If you bought an aftermarket pump, it comes with a thick piece of hose that may turn into mush in a short time. Pay a few extra bucks and get ac delco.

[Keith Seymore]

Originally Posted by tex_waco_usmc

As the title states... 86 GMC with 87 tanks and drivetrain (350 TBI with 700R4). Drivers side tank and sending unit are brand new and work perfectly. Passenger side got a cleaning (as best I could) and new pump. Worked good at first except the sending unit reads right when it feels like it. Now it wont even idle for long when running on the passenger side tank. She always starts right back up but wont idle. If you are driving and have to let off to brake and/or coast she dies. This only happens when running on the passenger side tank.

So confused. Any help would be greatly appreciated.

One other thing you might try for diagnostic purposes is to simply by-pass the switching valve with a short section of fuel line.

If it will run on the passenger side tank with the bypass fuel line then you know everything else is ok (ie, valve bad but in tank fuel line/pump would be proven ok).

K

[tex_waco_usmc]

Originally Posted by Keith Seymore

One other thing you might try for diagnostic purposes is to simply by-pass the switching valve with a short section of fuel line.

If it will run on the passenger side tank with the bypass fuel line then you know everything else is ok (ie, valve bad but in tank fuel line/pump would be proven ok).

K

Good call Keith! Never thought of doing that! Ill try that first!!!
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