302 V8, Dual tanks. A few months ago the truck stopped running on the front fuel tank so have been running on the rear tank only. Now all of a sudden the engine barely stays running as long as I sit and pump the gas peddle. Fuel is comes out the bleeder valve at the fuel injector rack although haven't checked the pressure. Replaced the pressure regulator. Didn't fix the problem. Replaced the fuel filter. Replaced the rear tank fuel pump. Didn't fix the problem. Can here the high pressure pump come on when ignition is turned on. Is there something else that might be going on electrically that is keeping me from getting adequate fuel supply or could there be something other than the fuel system that's causing this problem? Also, what the heck is that canister behind the high pressure pump on the frame with all the fuel lines running in and out. Looks like an oil filter and says "do not remove cap" on the side (which I removed and broke the gasket so now it leaks gas all over cause I can't get it to seal up) and have to try to fix that problem too. If I can't figure this out soon I'm going to try a firecracker down the tank. Any suggestions?

 

With regards to the strange looking canister inline before the high pressure pump - the Haynes manual refers to it as a 'fuel system reservoir'. Mine leaks pretty bad. A response to an earlier post I had made in the fuel forum suggested replacing the o-ring which makes the canister seal to the top where all the fuel lines come and go. My only problem is that the folks at Advance and Napa look at me like I'm an idiot when I describe the reservoir and then try to sell me a fuel filter or regulator. It seems like I saw an old post where the guy picked up one at the dealer.

 

Jason,
Thanks for the reply. Someone told me there was a filter inside that reservoir. That's why I took it off thinking maybe it could be replaced but when I did, there is nothing inside but fuel. Now the o-ring wouldn't stay put when I tried to put it back on and I ruined it. Will try to get one from the dealer and glue it in place or something. Any thoughts on what might be causing my engine problem? I think a lot of people have this same problem but haven't found a post that tells how to fix it other than to check and replace the internal tank pump, regulator or filter which I already did. This is weird. Anybody know if the fuel pressure relay might be causing it and where it is cause I don't have a clue what it looks like and where it is.

 

That is called the Dual Function Reservoir, it has two incoming fuel lines (one from each tank), one outlet to the engine, a return from the engine, and two returns (one to each tank). The reservoir switches fuel flow between the two tanks by utilizing an internal diaphragm that is pressurized by either of the incoming fuel lines.
There is also a 20 micron filter in there.

When fuel comes into the top side of the diaphragm from the front tank, it pushes the diaphragm down, causing the valves in the reservoir to close the rear tank supply and return port. When you switch to the rear tank, the front pump shuts off, and the rear pump flow goes into the bottom side of the diaphragm, switching the valves the other way.

If the diaphragm is ruptured, or if the valves are messed up, it could cause a restriction in flow, or improper switching between tanks. You may have to replace the Dual Function Reservoir.

Also keep in mind, that there is a low pressure pump in each tank, that feeds the reservoir, in addition to a frame mounted high pressure pump that draws from the reservoir.

This info is from 1988 Ford Service Manual, I believe it is same for 1989.

 

this must have been discontinued in '90 or 91. My '91 does not have the resorvoir OR the high pressure pump mounted on the rail I keep hearing about. I think Ford had some problems with is as part of the recall on fuel cross over and spillage. So I take it that mine has "std" or high pressure pumps in both tanks.

 

Babarche,
That was good info there. I stopped by the Ford dealer and got a new o-ring to put in the canister. They say they are almost impossible to re-install. They want me to buy a new one. I will take the unit out and check the diaphram and filter before I do that and while I'm at it try to put the new o-ring in without breaking it. Maybe try some grease to hold the ring up at the top of the threaded area until the canister is screwed up tight. Also am going to check to make sure I put the fuel filter in the right direction although don't know if installing it backwards would cause a problem. Still no-one has answered my question about why the engine doesn't seem to be getting enough fuel to stay running. I was wondering if there could be another problem with a relay, mass airflow sensor, computer or something else electrical that might be causing the symptoms. Front tank doesn't pump fuel, wrote it off. Replaced pressure regulator, filter, rear tank fuel pump. Fuel comes out at fuel injector rail bleeder valve and high pressure pump sounds like it's coming on with key turned on but have to pump gas peddle just to keep the truck running. Any help/ideas would be appreciated.

 

Re: not running -

You might check your return lines to the tanks. I was working under my 89 Bronco, and nicked the return line somehow - put a pinhole in it. Didn't notice, went to start it up and it would barely run. Since the fuel system is a closed system, the pinhole was acting like a pressure relief of sorts. Found and fixed the hole and it still wouldn't start. Opened the pressure relief valve on the fuel rail, cranked the engine 'til fuel showed, tightened the valve and it started right up and ran fine.

Just a thought

 

Go borrow a fuel pressure gauge from Autozone or whichever local parts store offers loaner tools. Hook it up to the Schraeder valve on your fuel rail, and see what the pressure is before cranking and when running. Just because you see fuel at the Schraeder valve does not mean you are getting adequate flow.

(The pressure is a result of flow against a restriction. The fuel pressure regulator provides a variable restriction to flow by controlling a metered orifice between fuel rail and return line back to tank.)

If your Dual Function Reservoir is restricting flow, you will not have enough fuel available to your high pressure pump to create proper fuel pressure in the fuel rail. Use the gauge to see what pressure is in the rail. It may show that the pressure is building up before you start the engine, but as soon as the engine starts using fuel, the pressure drops because there is not enough flow to maintain the proper pressure (about 39 psi) with engine running.

If you can rig up a line to bypass the dual function reservoir, you could determine if it is posing a restriction. Replace the DFR if it runs fine when bypassed.

And yes, they changed to a different system after 1989, eliminating the low pressure pumps and DFR, and going to one high pressure pump mounted in each tank, with check valves integrated into the pump assembly to control return flow back to the tanks.

 

Well I spent the afternoon ripping the dual function reservoir apart and checked the diaphram which was good and the operation of the check valves which seemed to be working ok although a little stiff (valves are under spring loaded pressure). Also fixed the leaking canister with a new o-ring. I made sure the diaphram was in the up position thinking it would feed from the rear tank where I replaced the pump. I found a small rubber o-ring sitting in the bottom of the canister (a little smaller than the diameter of a pencil) which did'nt look like it belonged anywhere. Now the truck won't start at all even after cranking it for the duration of my battery life. Could be not enough fuel has cycled through or I put the diaphram in a position where it's trying to draw from the tank with the bad pump in it. Still getting fuel out the schraeder valve though. I'm going to take your advise and get a pressure tester to see what kind of pressure I'm really getting and check to make sure there are no holes in the lines. I'm still wondering if it might be a computer, sensor, or relay problem though. Once I check the pressure, if it turns out ok, then I'll know it isn't the high pressure pump or reservoir and has to be something else since I've changed everything else in the fuel line. I'll keep coming back here to report what I find as a record for anyone else who might be having the same problem in the future and hope someone may be able to add in some ideas about what might be causing this problem. Trying to do all this between soccer, football practice and collecting firewood for the winter (with my borrowed truck) so might take a few days to get it straightened out.

 

 

I'm having the same issue with my engine in my '88 f150 and took off the line that goes to the filter and found out I have water in my front tank(i dropped my rear as a process of illumination). Check for that. As to the dual function thingyabober, I took the canister part off and discovered to filter inside so i dunno what's up with that. I tihnk ford replaced both these items(the crossover and master pump) with a stand alone electric crossover valve. I'm not 100% sure how to go about replaceing those with the valve, but they can be bought from J.C. Whitney for a fair price.

-Matt