Hello, I am new to this website and need some help. I have a 1989 Ford F250 with a new 351 (5.8L) it has duel tanks, but only the front tank operable. I have bypassed the FTSV and only going to the front tank while still using the FSTV just the ports for the rear tank closed off and the rear tank fuel pump disconnected. I am currently having a problem with the High pressure fuel pump (on the rail) and front tank fuel pump still making their high pitch priming noise after the one to two seconds they are suppose to start up and shut off when the key is turned to the on position but not started. I have disconnected the fuel pump relay and turned the ignition to on position and still both pumps make their noise continuously. I also had the fuel pump relay and EEC relay unplugged turned to on position same thing, both fuel pumps still doing their thing continuously. All this stops when i turned the key to the OFF position. The truck starts and runs, but I am no mechanic but I didn't think the fuel pumps work this way. If anyone has any suggestions for me to look at that would be great?

 

Sounds like someone bypassed the fuel pump relay.

 

How do I find out if someone has bypassed the fuel pump relay?

 

Have you had the truck for awhile and this just started? Or did you rebuild the engine before having had the chance to drive it previously?
If it's not some sort of a bypass on the relay (I think that would be done in the fuse and relay box, but not sure) then the usual suspect for a pump running on is the computer itself. Usually a burned trace or leaking capacitor.

What's the history of the truck? Original computer, or replacement? If a donor from another vehicle, what type?

Paul

 

It would not be the computer if both the fuel pump relay and the EEC power relay are unplugged.
The computer would not be getting any power so it could ground the fuel pump relay even if it had bad caps or a bad trace.
I would start by looking at the wiring under the two relays.

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I do not know the history to much on the truck. I bought it from an older individual (original owner of the 89 truck) to help him out for medical reasons. I bought it to work on our farm. The man's son had put a dump bed on it to dump firewood beside his wood stove. I also wanted it for the hydraulic dump and the four wheel drive combination for the farm. For the history on the truck I do know he replaced the motor five years ago and it has sat for the last 15 months before us buying it from him. He hand cleaned the tank and put a new front fuel tank pump on prior to us buying it all new fuel filters and fresh new fluids all throughout the truck oil, trans case, transmission, etc. The hi-pressure fuel pump was replaced a year before us buying and the 15 months of sitting. Seems to be the original computer. I have been on vacation but I will call the original owner after work tomorrow to find out more information on maybe bypassing anything when he put the 351 crate motor in himself. He builds cars from the frame up so he will know or remember anything he might have bypassed on the truck. but when i returned home I went to get in the truck and neither one were humming and the truck would not even start I got to doing some research on the wiring like subford said and found out there was a 30 amp fuse got to hot and exploded so i replaced it and the both pumps started their humming again even with both relays unplugged truck idled good but it was getting way to much fuel when the gas was pressed and the hi pressure fuel pump was so hot you could not even touch it. never had the problem of getting to much gas. the truck ran good the first two days we had it on the farm.

 

The best of my knowledge and following wires from below the relay by the diagram given, no bypassing has taken place.