My 1990 F-150 Haynes manual says that when you turn the ignition to ON (but not to start), the fuel pump should come on for 1 to 2 seconds. This results in an "elects check" of the EEC. My Ford's fuel pump with increasing frequency will not shut-off but continues to run. Secondly, when it does this and you continue to the start position, the engine will fire for only a second and then simply continue to crank without starting. The Hayne's book says that if the pump does not operate for the 1 or 2 seconds as designed, the fix is "check with Ford, the EEC may be bad."

My question is: Is there any input from outside the EEC that signals to it to cut out the ground it is providing to the fuel pump relay (because that is what completes the circuit that allows the fuel pump to operate for 1 to 2 seconds), OR is the 1 to 2 second grounding a timing function controlled entirely inside the EEC and I may have to replace it?

Thanks in advance for any advice

 

My 89 truck was doing something very similar with the fuel pump failing to shut off. Didn't matter whether the key was on, in, or not. I finally figured out that I had a loose connection at the fuel pump test plug (on the driver's side fender well). Once I cleaned the connection, never had any more problems with it. Next time it continues to run when you turn the truck off, try tapping on that block of connections. If it quits, that's probably what it is.

My guess would be that its a loose connection problem rather than the EEC bad.

 

thanks M04 for the reply......the pump does turn off when the key is turned off. I have cleaned/inspected all the connections I can think of - including the EEC.

 

This sounds more like the realy is going bad. Over time they can get corrosion from the arcing that occurs, and sometimes even weld themselves in the on position.

 

Agree with pfogle that it's relay.Eventually pump will run after you turn off switch and then you'll have to "smack" relay to shut off pump.

 

Thanks for the thoughts but two things seem puzzling....first when the pump keeps running the engine wont start???? everytime I turn the key off the pump shuts off...

It seems if a sticking relay causes the pump to run, then the engine should still start. Also once in awhile the pump should keep running when the key is turned off - which it never has done....

thanks again

 

If the relay sticks the fuel pressure gets too high and floods the engine.

 

^ not really. The computer runs the fuel pump continuously while the engine is running. It only turns it off if it does not sense engine rotation. It would not flood the engine if the FP relay stuck on. I do agree that the relay could be sticking, but it wouldn't cause the no-start condition.

tddiller, Have you tested the TFI module?

 

When the key is first turned on, the EEC is reset. The hardware reset causes the FP line from the computer to go low, which energizes the coil in the fuel pump relay, which in turn provides VPWR to the fuel pump, which causes the fuel pump to run.

One of the control program's tasks is to monitor the PIP signal coming from the TFI. If it does not see PIP for two seconds, it de-energizes the FP line, which should shut off the fuel pump relay. This is the behavior that you observe when you turn the key from off to on, but do not attempt a start.

If the computer will not reliably run the control program, it may not be able to carry out this task, and the fuel pump may be left running. It may also fail in its other task (controlling the fuel injectors) and it may give the "no start" behavior you observe.

The easiest way to diagnose this is to attempt to collect KOEO codes (see fordfuelinjection.com). Flashing the check engine light is another task for the control program. If it can control the light, it should be able to control the fuel pump. If it can't control the light, it may be dead.

If you can get codes from the computer, but the fuel pump runs when it shouldn't, suspect the fuel pump relay.

The computers almost never go bad. Poor connections, lack of power or ground to the computer, bad sensors, etc are the typical culprits. I suspect many of the EEC rebuilders are able to test and repackage more than 75% of the supposedly "bad" EEC cores they recieve -- without changing or fixing anything.

But on the other hand, sometimes they really do fail, and this may be your issue.

 

Thanks for the responses fefarm and EPNCSU2006, I think I will look at the TFI and the PIP signal specifically. Knowing a bit more about the programing inputs is exactly what I needed to know. I do get engine codes correctly and I do have two FP relays with both subject to the occasional FP running beyond the two seconds. Very unlikely sticking is the problem. When the pump runs beyond the two seconds, my meter tells me the ECC is still running low which keeps the relay engaged and pump running. I agree the ECC failing is the least likely case and that is why I wanted to explore all other possibilities before laying out that cash!!! Knowing the PIP may play a role, I will check it out.....thanks

 

If you replace the PIP get it at napa or the dealer. I went through 4 of the autozone ones in a month, before getting a good one at carquest (about $10 more).

 

It would be fairly hard for the TFI to cause the fuel pump to run when it should not. The PIP signal it produces is a pulse. The absence of pulses is what is supposed to cause the computer to shut the fuel pump off. So if you completely disconnect the TFI module (rendering it utterly dead from the computer's point of view), the fuel pump should shut off after two seconds.

In order for the computer to leave FP low, it would have to think there are pulses coming in on PIP with the engine stopped, which seems like an unlikely failure mode for the TFI. The next time time it does this, try disconnecting the TFI module harness connector and see if that causes the computer to recognize the engine is not running.
I bet it won't make any difference.

 

Hey Fella: I had the exact same problem with my 1992 4.9 just last week. I tested and checked out everything, never did get a related code. finally I pulled the computer and found that water had entered the seal gasket and rusted the computer mounting rack. I dried out everything and OSPHO treated the rusted areas of the frame rack, sprayed out the harness connectors with CRC silicone electrical spray and reassembled all. Powered up and all is working fine.Before when I turned on the key the fuel pump would run non stop and sometimes it started and stopped by its self; if I tried to start it would not stsrt or would die immediately; now the pump runs for about two seconds and stops and when I turn to start the engine starts immediately. Looks like it was a bad ground?
Now my current problem is light surging at any and all speeds with a slight miss at idle. I am going to check the rest of my grounds at battery and start testing sensors after I install a EGR restrictor plate.

 

I think we both stumbled on the same possible fix. I too ended up pulling the computer and all three of the bottom pins were corroded. (Due to dirt and moisture over time) Two of the those three pins are in fact grounding pins! Haven't had the problem since!!! Sounds like you are more up to speed on troubleshooting than I am. Good luck on your current problem. If isolating the EGR doesn't have any effect.....a clogged/stuck fuel injector might be worth looking at.

dave