I had been posting this in an older thread which was getting off the topic.

About 5 weeks ago I replaced the Front Fuel Pump in my 90 F150. It ran and started from the tank. Recently I began to use the tank, but the engine kills at stoplights that take all day (longer than 1.5 minutes). When I replaced the pump I noticed how hard it was to blow air through the External Check valve installed by Ford during a 1993 Recall. But I installed it back anyway.

Yesterday I brought it into the shop and did a fuel pressure check as described in the Haynes 17 Model Year Manual. I did not jump the pins on the diagnostic plug to get the pumps to run continuously. My results were as follows from each tank.

Rear Tank, Turn Key on (engine off) pressure goes to 54PSI and after about 60 seconds drops to 53PSI. Running at Idle with FPR connected 49PSI, Running at Idle with FPR disconnected 59PSI.

Front Tank (with external check valve in place), Turn Key on (engine off) maybe 10PSI ... turn on about 8 times and it will build to 30PSI. Not enough to start engine. Start from rear and switch to front tank Idle with FPR connected 34PSI, will get up to 45-46PSI at above idle speeds but drops down to 30 before going back to 34 or so when returning to idle. With FPR disconnected it is about the same.

Front Tank (with external check valve removed) Same as above.

I should have checked the pressure coming directly from the front tank and not just from the fuel rail, but didn't have everything I needed to do this.
The previous pump had the internal checkvalve problem allowing return line fuel to enter the front tank when driving from the rear, although I did not check the pressure from it, it seems to have performed about the same as the new one does when running from it, lack of power, almost dying at a stop light.

Subford, you have been very helpful here and I would like to hear from you and others as to what I should check next?

 

I think I remember you saying you replaced the whole Fuel delivery module and not just the pump in the front tank.
If this is so then you do not need the external check valve and you can use the one in the fuel delivery module.
If you just replaced the fuel pump inside the fuel delivery module then you will still need the external check valve.

The pressure fuel line from the front tank just "T"s with the pressure line from the back tank and then goes to the fuel manifold.
The fuel pressure regulator is after the fuel manifold and the bleed off goes back to the tanks in a return line that "T"s off to each tank and enters the fuel reservoir in the fuel delivery module of the supplying tank if the shuttle valve is open in the module.
So the fuel regulator is OK.
If you replaced the fuel delivery module in the front tank and removed the check valve and you get these fuel pressure readings then take it back to Ford (auto parts stores do not have them, just the pump) and get another one.

 

I just replaced the pump ... not the whole thing, but the pump is what contains all the internal check valves on the fuel delivery module. I am going to try it just from the pump .... I don't believe any of the fuel lines are restricted ... if they are then they were before also. I am sure if the return side of the pump was plugged up .... the FP would be much greater, I wonder if that external valve caused a problem.

Did they change the fuel delivery assembly after the recall that changed the pumps, I mean the other parts of it other than the pump, they looked the same.

 

Wrong! The valves are not in the pump. They are in the module.They did not do anything to the fuel delivery module or the tank in the recall, just replace the FPR and add the check valve to each tank pressure line.

Your problem is that you replaced the pump and not the fuel delivery assembly (module) and then remove the outside check valve.

I know it cost about $350.00 from Ford but I do not know what else to tell you.

 

Subford

This is what I replaced ... the new one was not as brown, guess that is what gasoline does to it after several years.

I did not see any kind of check valves in the metal disc, tubes and crossbrace that I took off of this and put on the new pump assembly. Are you saying that other than that external checkvalve that I removed, there are other check valves in the entire fuel delivery module other than those in this part?

 

That is your fuel delivery module and there are three valves inside of it.
It has a Hi pressure check valve, shuttle valve, and a reservoir check valve.

With this part new there should be no other valves outside of the tank (or fuel delivery module) going to the fuel manifold.

I though I have already posted a diagram of the fuel delivery module if not here is a diagram:
http://i54.photobucket.com/albums/g9...yAssembly2.gif

 

Yes, I have seen that posting I think .... can't see photobucket from work computer. I didn't know the pump inside of that could be replaced, or at least ordered. Replacing that did stop the crossflow problem from rear tank to front, now just need to figure out why the delivery PSI is low. Will try troubleshooting directly from the pump first, what is the best way to do this, should I put a rubber hose to a fitting with a shreader valve and take PSI off of that, or should I use the above and have another hose coming from past the shreader to the return line side of the tank to test it?

 

By the way if the hi-pressure check valve(s) is bad on the back (rear) tank and you are running on the front tank the fuel pressure will be low.

Also if you run the hi-pressure line just into a gauge and not hooked to the trucks hi-pressure line the pressure can and will go as high as 100PSI.

As far as I know all (most) auto parts store just sell the fuel pump and you have to take the fuel delivery module apart (not easy) and replace the fuel pump inside.

 

I have that same external check valve on the rear tank .... so I am guessing it is not getting in that way. I have run on the front tank on the highway, it gets up to the bottom of the recommended PSI at above idle speeds, I have not noticed fuel transfer to the rear tank, at least not in mass quantities like I had going to the front through the return side.

I know it can go rather high .... I guess if I do it, it will only be for as long as the initial prime when I turn the key on .... if it doesn't shoot up then I know it is the pump. I guess I can also do a flow on it also ... have to find how many quarts it should pump in a set time.

Every place I looked for that "Pump" had that whole assembly, when you talked about the Fuel Delivery Module I just thought it was the whole enchilada .... float, sender, pump assy and top part with the fuel tubes.

If it is something in the fuel line, I should be able to disconnect from the pump and filter and run a piece of wire or compressed air through the line without any screens getting in the way. Right?

 

Right you are.