Truck revs up or plays with its fuel pumps.

[subford]

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.

 

[Skandocious]

Well first off Bill-- glad to see your light on again! Unfortunately I think if you can't figure it out the nobody probably can, lol! That being said, I have to ask the most obvious question since you didn't mention it-- have you checked the fuel pump relay?

 

[subford]

Well first off Bill-- glad to see your light on again! Unfortunately I think if you can't figure it out the nobody probably can, lol! That being said, I have to ask the most obvious question since you didn't mention it-- have you checked the fuel pump relay?

I do not go to all the sites as much anymore and post as I have been in and out of the hospital and getting close to 70 years old. Been doing some posting over on an RV site for the Ford F53 from our era.

I 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.

Something else it does if I start the KOEO self-test sometimes it will not power on the fuel pump relay when the test starts. But always powers the fuel pump relay for one second each time the key is turned on.

This all seem to start happening at the same time that I found flower bulbs setting on top of the heater/AC box. But can not find any chewed wires or vacuum lines as I have looked and looked.

 

[5.0Flareside]

Sounds like a a loose connection somewhere in wiring.. But idk for sure

 

[subford]

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. 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.

Hot wired:

/

 

[subford]

Well it is still doing even when it is hot wired so I guess it was not the Ignition Switch.

 

[subford]

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.

 

[Dukes78]

I don't know alot about fords but thought I would just ask. Does it have a pressure regulator, and if they do is the fuel system the type that when the key is on it will try and keep a constant pressure on the fuel system? To me sounds like leaking fuel pressure regulator causing the pump to keep cycling on to maintain pressure. Also a leaking fuel pressure regulator that is vacuum operated will cause the vacuum system to suck up the leaking fuel. Like I said dont laugh if im way off on this as I have never done much ford stuff I was a GM mechanic for several years that ran systems like this.

 

[subford]

I don't know alot about fords but thought I would just ask. Does it have a pressure regulator,

Yes it does.

and if they do is the fuel system the type that when the key is on it will try and keep a constant pressure on the fuel system?

No it dose not. The pressure regulator just returns fuel to the tank when the fuel pressure over comes the spring and pushes the valve in the pressure regulator off its seat. If the engine is running vacuum will pull against the spring to let the fuel pressure go lower.

To me sounds like leaking fuel pressure regulator causing the pump to keep cycling on to maintain pressure.

The pump is only turned on by the computer and the computer has no idea what the fuel pressure is. There is a clock inside the computer that times the fuel pump on for one second each time the computer sees a PIP from the distributor. The fuel pump runs at no other time except for one time for one second each time the computer is initiated.

The problem was the computer keep getting reinitialize with the tuck just setting with the key on or when the engine was at idle.
This was being caused by two wires shoring together in the starter wiring harness right next to the starter. Just guessing but I think it was the heated O2 sensors return to the computer wire being shorted to power and this was causing the computer to reinitialize.