I have a pretty good mechanic who appears to be stumped about a fuel pressure problem on my 1988 F250 with dual tanks.

The rear tank and low pressure pump were replaced in the summer of 2007. I truck sits all winter (started once a month) so I have only put about 3000 miles on it since the new tank.

When I picked it up a few days ago it would hardly run very poorly on the rear tank. I thought it was bad gas or water in the tank so I ran the truck for a day and a half switching from the front tank to the rear tank. Finally, I got the truck to the point that it would run about 10 miles on a level road without much problem - but give it the gas or hit a hill and it would stall.

Well, with all this screwing around on my part - the switching back an forth between the tanks - I got the front tank to begin sputtering.

So I take it to the mechanic whose been checking the fuel pressure and can only say that he can get the front tank to lose pressure very intermittently and the rear tank can't seem to maintain pressure (all this pressure is being measured after the high pressure pump). The gas is good and clean so he doubts that the rear tank has pumped some crud into the filter. He's beginning to think that it is some type of electrical problem and has been honest enough to admit that he hasn't had much experience with the wiring of this beast and that's where we're at ...

Any ideas? Much thanks - I'm on vacation and having the truck and camper in the shop is a drag.

Thanks, DR

 

When a truck with your type fuel system sets the "O" rings in the selector valve stick and cause problems.

As for the wiring your year truck has problems with the wiring under the Fuel Pump and EEC Power relay sockets.

Here is a diagram of your electrical and fuel piping systems:





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Subford,

Thanks for the informative reply - I'll pass it along to the mechanic.

I don't have any first hand knowledge about this fuel system so I can't picture how these O rings work. But how would an O ring malfunction affect the rear tank only and not the front tank.

Thanks again, DR

 

the o rings in the selector valve go bad and return fuel back to the tank instead of sending it to the engine

 

The images below might help you to understand. What the "O" rings does is stick on the shaft in the position that they were at when left for a long time.

A stuck "O" ring:


The valve, yours will not have a filter in it, 86 was the last year for the filter:


How it works:



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Also on your truck check and make sure the small black wire with a green stripe at the NEG Post of the Battery has a good connection.
This wire causes a lot of problems.

 

Do they still make rebuild kits for that setup? If so who sells them? Im sure my 89 will need rebuilt as it has sat for the last 4 years during the rebuild.

 

One member of FTE said he found one and that was about three years ago.
He said somethig about that he work at a Ford assembly plant but did not go into details.

Most just order a new one from Ford when the valve goes bad.

You can also read about it at this URL:
http://www.stangler.com/motorsports/...alve/index.htm

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Most of this stuff is no longer available from ford. I have run in to brick wall after brick wall rebuilding my 1989 F250. Poor 89 is not so old that restore parts are being made and just to the age that ford has swept most info and parts building under the rug.

Try to find a new filter or high pressure pump mounting bracket for a 87 - 90 F- truck.

Oh well thanks. I'll have to start digging thought the net.

OK update I need to remove my foot from my mouth here. Just got off the phone with local ford parts. That item is still available from ford. $160.00 about with tax.