I've been searching this forum for some information on replacing the rear fuel pump in my 1996 F-250 but have been unsuccessful. The mechanic told me today that the pump is only supplying about 20 PSI to the engine and that the pump is weak. I'm not into spending $500 to have it fixed, and I was wondering how complicated it is to change the pump myself. Can anyone tell me how involved this job is, or how to do it?

Much appreciated,

Matt

 

First off it is unlikely that the pump is bad, they either run or they do not. I have not seen anyone on the Forum report a pump yet that did that.
You may need to change your fuel filter and that may fix it.
These pumps can put out 95 PSI against a blocked head.
You say it is a F250 so you may still have the OBD1 computer system. If so you can ground pin #6 of the EEC Self-Test connector under the hood while you have a fuel pressure gauge on it with the key on. This should give about 45 PSI for an eight and around 60 PSI for a six.

A replacement pump can be had for about $150.00 at most auto part stores and you will also need a disconnect tool to get the fuel lines off as you drop the tank. It is better if the tank does not have any fuel in it. But if it does you may have to use a floor jack to drop the tank.
Some think it easier to just pull the bed off and then just take the the pump out from the top.
There is a ring that you have to turn CCW after the fuel lines are removed and then you can unplug it and take the whole unit out.
After it is out you cut the wires to the reservoir and there should be a wedge that comes with the new pump to get the lines out of the reservoir. Just but crimp the wires back together again. Push the reservoir on to the fuel lines and then put it back together again.

This type works best for me:




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It's as hard as removing the bed. Once the bed is off the fuel pump is nothing to replace. Six bed bolts, two tailights and the fuel fill hoses. Two grown men can lift it off the frame, but it's still kind of a pain. If you have access to an engine hoist use it.

 

I have never done it but the most difficult thing is getting access to it. You would have to either drop the tank or lift the bed off or jack the bed up. After that you just disconnect the wires and pipes, remove the retaining ring and lift the pump out.
Someone else may give more info.

 

I agree with Subford . But if you ever do a pump I took off my bed like Skaterbro, to me its just easier. Subford always has great info & pictures

 

Subford,

Thanks for your reply. Now the truck runs great when it's on the front tank, but when I switch to the rear I have a loss of power. Are there any other ways to tell if the fuel filter is the problem in this situation. I just picked it up from the shop and didn't have them change the filter. He didn't seem to think that would make it run better. Is there a filter for each tank? Are they simple to replace yourself?

Thanks again,

Matt

 

You only have one fuel filter for both tanks.
So I guess your fuel filter is OK.
You may have a bad Fuel Tank Selector Switch on the dash or a plugged fuel filter sock in the tank. I would check the voltage at the tank plug to see if it is low. Other than that and the sock he may be right but as I said I have never heard of one going out that way. Also look for a pinched fuel line coming off the rear tank.

I wonder if he even had 20 PSI from the rear tank pump. Put your ear up to where the gas cap screws on after you take it off and have someone turn the key off & on a few times without starting the engine. See if you hear anything. I bet the pump is not running at all.

 

Thanks, I will give the key thing a try to see if the pump is running. Forgive me for my ignorance, but how do I check the voltage for the rear tank fuel pump? I'm not really much of a mechanic, but I do have a multimeter and know how to use it!

 

i have had several fuel pumps go out on me, and none of them have gone out the same way. some have died on me completely, another has died and then will keep coming back to life, and i have had others that will work but only half ***.

if you determine that the pump is bad, i would definitely take off the bed and go in from the top. its not that bad, i did it with the help of only my gf. instead of trying to lift it off, we just slid it about 3/4 of the way off, enough to get access to the tanks.

 

Unplug the fuel pump/sender plug near the front of the tank and by the drivers frame rail.
Check the power on the Brown wire with a white stripe to the Orange wire. The Brown wire with a white stripe is the power wire and the Orange wire is ground.

If your truck is over 8500 GVW and not a California truck then you will have the OBD1 computer system. Then you can ground pin #6 of the EEC Self-Test connector under the hood and turn on the key. This will keep power on to the selected pump circuit for testing.

I will not go any farther not knowing what size truck you have.

 

Thanks for all the info. I will try the fuel tank plug test. The trucks GVWR is 8600lbs.

 

Ok the plug looks like this:


And is located (Diagnostic Self Test Plugs):

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Subford,

I did your diagnostic test tonight to and the voltage that I read on the rear tank wiring harness was 11.8 volts, which I would assume is pretty much right on. Does this indicate that it's the pump or are there more things I should try?

Matt

 

It would be a bad pump, sock or pinched fuel line.
You need to take the FDM (pump) out to check the sock and if the sock looks good I would replace the FDM.
But check for a pinched fuel line first from the tank to the "T" connection on the frame.
Also make sure nobody has added a check valve to the pressure line coming off the top of the tank.

The FDM:


The "T" Connection:


The added check valve looks like this:


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Ok, I will check the lines and the junction between the two tanks. What exactly is the sock? Does the bed have to come off to check that? I assume that the only things I can check without removing the bed are for pinched fuel lines and a check valve.

Thanks,

matt