My 1996 F250 4X4 5.8 liter will not stay running on its own. It will run for a few seconds and then run rough and then cut off. If I spray starting fluid into it, I can rev it up to high RPMs. It has a new fuel pump (which I can hear run) and a new fuel filter. I have pressure in the fuel bar. I have tested the fuel regulator. It is throwing codes for system normal (111-111). I have also checked the MAP sensor. I was told by a mechanic friend of mine that it is the computer. When I checked one of the injectors with a test light, it WAS pulsing.
Can I get a pulse indication on the test light from the injectors and still have a bad computer?
Any further advice would also be appreciated.

 

You need to put a gauge on the fuel rail to see exactly how much pressure you have, the system has to build and maintain 40psi or the engine will have problems. If the pressure is low or bleeds off you could have dirty or stuck injectors or maybe the fuel transfer problem where half the fuel from the active tank goes into the other tank. Any smell of fuel in or around the truck? How is the milage? Does it have dual tanks and do they both work?

 

I told you to check the fuel pressure in the other thread you started: https://www.ford-trucks.com/forums/1...250-codes.html

 

There is no smell of fuel around the truck.
I only use the truck for hauling my boat to the ramp and/or gas station which is only about two miles away so no good indication of fuel milage.
I have dual tanks and I only use the front tank. When I switch to the back tank, the engine will not run. I figured it was the fuel pump so when I replaced the pump in the front tank, I figured I would only use it and avoid the hassle and cost of dropping both tanks.
I will try to verify the fuel pressure today for a more accurate number.

 

I went and bought a fuel pressure tester. When I start the engine I have about 20 PSI after a few seconds the PSI drops down and the the engine starts to run rough at about 14 PSI and then it cuts off within a few seconds. Beside and above the fuel rail there is something with a two-wire electrical connector and what looks like two small vacuum lines, one white and one green. The item has a little cap on top with a filter inside of it. When the engine cuts off I can hear this thing seeping air. If i put my finger over the little intake in the middle of it, the sound stops. What is this? Could it be the problem?

Sorry rla2005, I was being a cheapskate and trying to avoid buying the fuel pressure tester.

 

I am a cheap bast**d myself. Many auto part stores rent out tools like a fuel pressure tester. Your fuel pressure is way too low. Could be a fuel pressure regulator problem or a bad pump. A leaking injector will allow the pressure to bleed off after shutting the truck off. Unless you have a bunch of them stuck open I doubt it is causing your low pressure issue. If the rear Fuel Delivery Module (FDM) has a bad shuttle valve it could allow the front tank to fill the rear tank. That is why Paul asked you questions related to the fuel transfer problem that is so common on these trucks.

The part you are referring to is the EGR Valve Regulator (EVR).



The noise you described is quite common with these EVRs.

 

A little more info...
The rear fuel pump does not make any sound when the ignition is turned to run. With the fuel switch on "rear" and the ignition turned to run, I checked the voltage at the connector before the rear fuel pump and was getting around 7 on the pins. With fuel switch turned to "front" I got 0 on all of the pins. It appears that I am getting current to the rear pump so maybe the rear fuel pump is shot.
I turn the ignition to the run position, fuel switch on "front" and the fuel pressure at the bar goes to around 20. After the relay cuts the fuel pump off (2 seconds) I turn the ignition switch to off and back to run. The pump turns on again for about 2 seconds and the pressure goes to 30. I repeat one more time and the pressure goes to 40. The pressure then slowly bleeds down to about 20 after maybe 10 to 15 minutes.
Could this be related to the dual tank fuel system?
Could it be a stuck injector as was mentioned earlier?
I'm just wondering if my next step is to drop the rear tank and put in a new fuel pump.
Any suggestions?

 

Two hours later and the pressure gauge is still reading 20 PSI.
Turned on ignition and pressure jumped to 30. Started engine and revved-up before too much loss of pressure and the higher the RPMs went, the lower the pressure reading. When I let off of the accelerator, and the RPMs came down, the pressure increased, but only to about 12 PSI. Then as usual within 5 to 10 seconds the engine cut off.

 

Simple test with the engine running: pull the vacuum line off the fuel pressure regulator. The pressure should max out around 45 PSI. If the pressure does increase it could be a simple case of a bad regulator. If it remain low then you most likely have something else causing your issue. Low fuel pressure can be caused by everything you listed above, except for a stuck injector the pressure typically keeps dropping to zero.

 

I had to wait until this morning to continue troubleshooting. I pulled the vacuum line on the fuel regulator and got a slight bump in pressure (about 3 PSI) and then the steady decline continued.
Next:
I built the pressure up to 40 PSI and then removed the fuse for the fuel pump. The engine ran for only about 10 seconds and then cut off. Earlier when I started the engine and got under the truck to listen if the pump was running while the engine was running (which it was) the engine ran for about two minutes before it cut off.

It seems like the fuel pump is working but just not keeping up.
Does this sound correct and should I just drop the tank and replace the fuel pump as my next step?

 

I am still wondering if the rear fuel pump module (FDM) has a bad shuttle valve. A very common problem on these trucks. In order to split the system in half others have been successful pinching off the fuel return line coming from the fuel rail. By doing this you eliminate a potential pressure bleed off point, i.e. the rear tank FDM. Personally I have never had the need to do this, but I would hate to see you toss another front pump only to find out it's the rear FDM causing your issue.

You can force the fuel pump to turn on by jumpering Pin 6 to ground (Signal return) on the Diagnostic Link connector under the hood.

 

Since Friday I have isolated the midship fuel tank and completely excluded the back tank from the equation (permanently).

Results:

Fuel pressure when key is turned on jumps to 40 PSI during 2 second prime. The engine will run like this forever. If I load the engine to about 3000 RPMs or higher (just a guess, no RPM gauge) the fuel pressure will drop down to below 20 PSI. If I continue with the acceleration, the engine will begin to falter.

The next thing I did was to unhook the vacuum line from the fuel pressure regulator and the fuel pressure jumps to 40 PSI and i can run the engine way above 3000 or 4000 RPMs (WOT) and the fuel pressure remains at 40 PSI and the engine does not miss a beat.

Also, when I pressurize the fuel system (40 PSI) and leave the truck for several hours, the fuel pressure will fall all of the way to 0 PSI.

Is the fuel pressure regulator somehow stuck open or is there something else that I am missing here?

 

I must be on crack!!!!
Now (several hours later) when I unhook the FPR, I get the fuel pressure jump from 30 PSI to 40 PSI but when I load the engine (above 3000 to 4000 RPM) the engine begins to falter.

Am I looking at a fuel pump (which is only a little over 1 year old) which is slowly dying?

 

Fuel Pressure regulator is cheaper and easier to change than a fuel pump. Yours does not sound very healthy. It may not be the root cause, but it looks like a contributor.

 

would a clogged fuel filter have anything to do with part of this ?