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.

 

My first question; Is the computer output turning the fuel pump relay on and off, or is it a power supply problem(EEC relay) cutting the fuel pump on and off.

 

The computer is turning it on and off.

 

Just a thought , do you think it could be a faulty ign switch , not the key switch , but the switch itself , you may have a bad or shorting ign contact in the switch .

Guy

 

I was 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. Replaced the Diode and Power Relay then hot wired it again and started it up again with no problem. drove it to town and back with no problems at all.
Then I pulled the hot wire and it has the problem again but the problem has been coming and going so I am going to put the hot wire back and try it again before I c/o the Ignition switch.

Hot wired:


/

 

Wow , nice , you know too much LOL , I was supposed to get those Caps today for my Computer Module , the tracking said they never left MD , so I called it in and they are trying to find my little package with those tiny Caps in it , does not look like I will be seeing them today , I am dis-appointed to say the least , got my surgery tools ready with soldering iron , I hope it gets here anyway today so I can see if that is the issue , I hope you find the problem , I will be curious to see what it is , have never seen that happen before with the fuel pump going on and off .

Guy

 

Put the hot wire back and it is still doing the rev-up with CEL flashing three times.

 

Sure you do not have any issues with the OBD1 plugs under the hood , oil or water in them possibly , just another idea , if it is not switch , it would have to be a short somewhere I am guessing , hot wiring must be bypassing the problem or pulling fuses is removing it from circuit .

Guy

 

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.

 

Glad you got it done

Guy