Can anybody come up with anything that would make the computer keep turning the fuel pump on and off over and over with the key just tuned on once with the engine not running?
It is like you keep turning the key on and off over and over but you are not.
Or it is like the computer is running the power up self test over and over.

It is a 1995 F150 5.0L 4R70W.
Tried three different computers so it is not the computer.
Changed the PIP sensor in the distributor three times.
Replace the MASS sensor.
KOEO self-test comes back with a 111.
CM comes back with a 111.
KOER reports Knock sensor not detected.
Check the voltage from the TPS as the throttle was slowly opened, .8VDC CT and 4.5V WOT.
Ref voltage 5.0V

When you start the engine it will start normal and if you let it idle the CEL will flash three times and the engine will rev from 750 RPM to 1500 RPM with the IAC going going from 38% to 58%. The high rpm will continue until you put it in gear then the truck goes back to idle.

Truck will lose power with the CEL/MIL light on when leaving stop sign and you have to floor the throttle to get power and turn off the CEL/MIL.
But this does not seem to set a code.

I though I had a good handle on these trucks but this one has me scratching my head.
Any help would be appreciated.

 

For the fuel pump problem, is this a single tank or dual tank? Does it do it on both tanks?

Either way pull the fuel pump relay, clean and test the harness connections, especially the ground and the control voltage which comes from the PCM relay, repair as necessary and re-install. If it's a single tank or it does it only on one tank, do the same for that fuel pump. If it does it on both tanks, the pump isn't the problem.

No idea on the other issues

 

Yes it has two tanks and it does it on both tanks.

Have replaced the PCM power relay and the Fuel Pump relay.
The computer once powered up should run the selected pump for one second and quit. But this one is powering the fuel pump relay over and over for the one second time out without starting the engine or turning off the key. So the fuel pump relay and the fuel pumps work OK.

 

...unless the signal to the fuel pump relay gets interrupted due to a bad connection, worn insulation, etc.

Since replacing the PCM and the relays didn't solve it that leaves the wiring harness

 

Check all of your GROUND wires.

Fords have a BIG problem with ground wires. If they get too corroded or rusty, they will not make good grounds and this can cause all kinds of issues.

On my 89 F150, the guy who had it though he had alot of issues w/ the truck not starting after it's been running. It did act like the starter was going bad.

But I got out there ( I HATE BATTERY CORROSION ) and cleaned each and every ground wire and ran 3 more of my own.

The truck starts right up each and every time w/o a problem.

Also, bad grounds can kill the computer or other electricial parts such as the AIC & ECM Modules ( From Personal Bronco II experience ) and can cause alot of faulty readings.

If you notice your truck headlights getting brighter / dimmer when revving the engine, this can also be attributed to bad / weak grounds as well.

I am not saying this IS your problem, but definately check it out.

 

I did check and clean all of the grounds when this first started.

Thinking it might be the Ignition switch so I hot wired the truck by pulling fuses "Q" & "U" so it would run with the key off. The fuel pump only came on once and then I started the truck. It tried to start to rev once with CEL/MIL only coming on one time. Shut it down and let it set for awhile. Then hot wired it again and started it up again with no problem. drove it to town and back with no problems at all.

Hot wired:



/

 

One thing I've learned about fords in 40 years, there' s no telling what causes some issues!

So many things can go wrong with wiring.

Do you know of anything that might have been hooked into the wiring system? I've seen a simple patch to create a power wire, or ground cause all kinds of electrical issues.

Does sound like you are working it out. Hope you get it soon.

 

No nothing has been patched into the wiring harness.
It is still doing it even hot wired to bypass the Ignition Switch.

 

The fix:

Problem fixed.
I think this can only happen to 1992-1995 5.0L engines as they are wired different than any of the other Ford engines.
The 5.0L uses the SIG RET wiring and the other engine use a different ground for the O2 sensor.
What the problem was that the heat from the exhaust manifold cooked the wires for the O2 sensor right near the starters wires brake out wires on the harness. I by passed the entire starter harness to solve the problem. I ran the bypass wiring from the plug at the battery all the way to the O2 sensor. My bypass wiring was from another 1995 5.0L truck that I had parted out. So it was just plug and play and a few wire ties. I do not know what wires in the starter harness was shorting to cause all of this as I am not going to undo that starter wiring harness and dig into it.