Dual Tanks Re-Hashing
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Junior User
Joined: Nov 2005
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Dual Tanks Re-Hashing
Ok I've searched all kinds of post and I'm not finding the info I'm needing.
88 F150 LWB 4.9L 35" tires, dual tanks, dual batteries, 4 speed tranny, etc, etc.
I had a problem with the REAR tank pumping fuel into the front tank and overflowing because the front pump was not working. The rear sending unit was not working either.
Soooooo I put on new tank up front, two new in tank fuel pumps, new mechanical diverter valve (from ford). so I have a new problem.
The sending units are working fine in both tanks and the rear pump is working excellent but is now pumping fuel into the front tank at twice the rate as before (higher pressure I suppose).
I'm going to get a new switch but I don't think this is the problem because I plugged the swith up backwards and it still won't switch tanks. Why is the rear tank still pumping into the front one.
Is there a external check valve or dirverter valve that I don't know about. What could cause the front pump to not get power? Does it have a seperate fuse for each pump does anyone have a breakdown of the fuel system and the wiring for it.
88 F150 LWB 4.9L 35" tires, dual tanks, dual batteries, 4 speed tranny, etc, etc.
I had a problem with the REAR tank pumping fuel into the front tank and overflowing because the front pump was not working. The rear sending unit was not working either.
Soooooo I put on new tank up front, two new in tank fuel pumps, new mechanical diverter valve (from ford). so I have a new problem.
The sending units are working fine in both tanks and the rear pump is working excellent but is now pumping fuel into the front tank at twice the rate as before (higher pressure I suppose).
I'm going to get a new switch but I don't think this is the problem because I plugged the swith up backwards and it still won't switch tanks. Why is the rear tank still pumping into the front one.
Is there a external check valve or dirverter valve that I don't know about. What could cause the front pump to not get power? Does it have a seperate fuse for each pump does anyone have a breakdown of the fuel system and the wiring for it.
Lead Driver
Joined: Nov 2002
Posts: 9,557
Likes: 44
From: Concord, NC
Each pump is fed from a common power source, which is diverted to one tank or the other via the selector switch in the dash. The selector valve on the frame rail is switched by fuel pressure from the in-tank pumps. There is a problem with the selector valve if fuel is going from one tank to the other. I had a failed in-tank pump, never had any cross-flow issue, but did run out of gas in the tank with the good pump because the valve had not switched to the tank with the failed pump. It is really odd that you are still experiencing this problem, even with the new selector valve.
