Question about Ford F-150

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I have a 1990 ford 150 that as daul tanks,the rear tank is the working one, last summer it decided that it wanted to stay on al the time. so i have using the feul tank switch to keep it from staying,acouple of weeks ago the switch and some of the wiring has melted,unusable. so i would just replace with a two stange switch, just straight wire the rear tank.

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I understand what you are saying but here is how I would recommend repairing the vehicle. You can wire the tank up the way you described but make sure you are tapping in from the fuel pump relay or you will burn up the pump and/or wiring. However you are losing half of your on board fuel capacity (19 gallons as opposed to 38 gallons). Here is how I would recommend repairing it.

  1. Replace the burnt switch and wiring. I would use a factory switch and wire it up how the factory intended.(See diagram for switch wiring) The new switch might correct your constant running situation and the front tank not working situation, but if not here is how I would procede.
  2. If the pump is continually running I would check the wiring visually for any exposed copper that could create a short and if that checked out good then try a new fuel pump relay.If you are positive that those are ok then consider replacing the vehicles computer.
  3. Once you get the pump running situation under control and you determine that the front tank is still not working, consider this. This truck has a fuel pump in each tank that supplies low fuel pressure to a high pressure pump on the frame rail. The fact that the truck runs on the rear tank means the rear pump and high pressure pump are working. So the problem is most likely the low pressure pump in the front tank. Replacing the pump in the front tank should bring you back to normal operation.
i have a 1990 ford - 42308314

Posted on Mar 18, 2011

  • Paul Fleming Mar 18, 2011

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The ford F150 uses a low pressure fuel pump in each tank, and that pairs of supply/return lines from each tank go to a reservoir unit. From the reservoir unit, a single pair of supply/return lines go to the high pressure fuel pump, which goes to the fuel filter and up to the engine compartment. -------------- For the front and rear tank not working.This problem is related to fuel tank selector valve.The fuel tank selector valve is bad.Its located on the frame rail between the tanks and the filter .If you replace this valve then you can select the rear and front tank and it will work as per that.But if you are running on rear tank and its working.But switch just got melted, then yes replacing the switch will solve the issue.But in that only rear will work.Because the selector valve is bad, the front will not work as required. ----------- Also the fuel tank selector switch on the dash panel performs two functions (as in a DPDT switch), with one side of the switch selecting which tank's fuel level sending unit is connected to the fuel gauge, and the other side of the switch selecting which fuel pump is active.To replace the switch, Take a small blade pocket screwdriver and slightly insert it between the dash and the switch. It should pry out and you will be able to get to the wiring to remove the old switch and replace the new.--------------- This should help.Keep updated.Thanks.Helpmech.

Posted on Mar 18, 2011

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