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Larry, Technical Editor
Category: Ford
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Experience:  Automotive tech editor & author, 30 years experience, ASE certified
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Fuel pump..the PCM module, ignition control module, fuel filter..sits

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When you turn the key to On, the fuel pump may run from 2 seconds to 2 minutes before it turns off. We replaced the PCM module, ignition control module, fuel filter, PCM diode with no luck. It seems like the longer the truck sits, the worse the problem. After 4 hours, it may run 10 seconds, after 8 hours, it may run 30 seconds. After the truck is started, there are no issues.

Any ideas?
The problem may be a bad fuel pump relay. The relay is weak and is not staying on when it is energized by the PCM. When the engine is running, the extra charging voltage may be enough to hold the relay on. The relay is located in the power distribution box under the hood.


Here's a description of the fuel pump relay circuit from the Ford SZservice literature. Maybe this will shed somelight on what is happening:

When the ignition switch is turned ON, the Electronic Engine Control (EEC) power relay is energized, providing power to the fuel pump relay for 1 to 2 seconds through the Powertrain Control Module (PCM) and an Inertia Fuel Shutoff (IFS) switch.

Fuel pump power is provided through the fuel pump relay contacts, if the PCM does not receive an ignition signal within approximately one second after the ignition switch is turned to the "ON" position. A timer circuit in the PCM will open the ground circuit to the fuel pump relay, causing the fuel pump relay contacts to OPEN. This action stops the power supply to the fuel pump.

When the ignition switch is turned to the "START" position, the PCM closes the ground circuit to the fuel pump relay, resuming operation of the fuel pump.

After the ignition switch is returned to the "ON" position, power to the fuel pump is supplied through the fuel pump relay.

The PCM monitors engine speed and opens the fuel pump relay ground circuit if the engine speed drops below 120 rpm.
Customer: replied 10 years ago.
Reply to Larry Carley's Post: I forgot to add that I have also replaced the fuel pump relay.
Then we can rule out the relay. That leaves a weak fuel pump as the only other explanation I can think of. The problem might be a corroded wiring connector at the pump, or a poor power or ground connection at the pump, too.

Customer: replied 10 years ago.
Reply to Larry Carley's Post: We did replace the fuel pump about 2 years ago. Doesn't it seem to reason that the problem would lie before or at the relay?

Reason being, if the relay is controlling the power to the pump, if the relay shuts off correctly, the pump could not continue to run. The pump is simply a motor. If the power is turned on to the motor, the motor will power, it won't run.

Unless the relay or PCM sends a signal to the pump and waits for a response before the relay/PCM would shut off the power, it does not seem logical that the issue would lie at the pump. I do not know if this is the case.

If the PCM sends a signal to the pump and is supposed to get a signal back, and it is not geting a response, so the relay/pump continues to run, THEN I can see that there may be an issue at the pump with either a connector or the pump itself.

It seems really odd, that the longer the truck sits after turning it off, the longer the pump runs. Tyr it right away after turning it off and it works every time. Let it sit 4 hours, it runs a little, 12 hours it runs longer.

Logically, it doesn't seem to be an issue at the pump.

Could it be an issue with the Inertia Switch? I have read that when turned on, power is set to the rely and inertia switch. The cable is connected at the switch, but could there be something in the inertia switch? It seems, the inertia switch and pump are the only two things I have not replaced.

Are there any other relays under the dash or in the cab that controls the PCM or fuel pump?
When the PCM energizes the relay, it has no way of knowing if the fule pump is running or not. On late model Fords, there is a fuel pressure sensor but not on your truck.

The PCM keeps the fuel pump relay energized for a second or two while the engine is cranking, then cuts it off the relay the engine does not start. If the engine starts, it keeps energizing the relay to run the pump. The PCM looks for an rpm signal from the engine to know if the engine is running or not. If it sees no rpm signal, it assumes the engine is off or has quit running and shuts off the fuel pump. This is a safety measure so the fuel pump doesn't keep running in the event of an accident, and the intertial shutoff switch isn't tripped to shut off the flow of fuel to prevent a possible fire.

So given all of this, it means one of several things:

The internal timer circuit in the PCM is defective -- but you say ou have replaced the PCM so we can rule that out.

The fuel pump relay is defective -- but you say you have replaced the relay so we can rule that out.

The PCM is not receiving an rpm signal from the engine -- that would cause a variety of driveability complaints like no spark advance, no injector pulses, etc. which does not seem to be the issue here.

The intertia shutoff switch is defective -- which is a possibility but the switch is either on or off. You could try bypassing the wirignon the switch to see if that cures the problem. If it does, replace the switch.

The fuel pump is weak and runs intermittently because of an electrical connection issue at the pump -- still a possibility.

Tghe fuel pump has a worn spot on the commutator that prevents it from turnign sometimes. This is a common fault. Try shaking or rocking the trunk vigorously. Sometimes this will jiggle the position of the pump armature just enough where the brushes make better contact with the commutator and the pump runs. Then try to start it. If the pump runs, you got a bad pump.

If the last pump failed because of rust inside the tank wearing the pump, it is certainly possible that the new pump may be failing from the same cause.

You've picked my brain clean. I'm out of ideas.

Customer: replied 10 years ago.
I don't think the fuel pump is worn. The pump definetly runs and you can hear it clearly. The last pump lasted 175,000 miles and the tank was clean inside. This pump has about 40,000 miles on it.

Once the truck starts, it runs issues. The problem always is the pump runs and takes longer to shut off. If you try to start the truck while the pump is running, it will turn over, but will not start. Once the pump has stopped, the truck will start right away.

Does this provide any more clues?

This problem is pretty consistant. When we replaced the PCM, ignition control module and relays, it seemed the problem went away for a day or two, and then came back.

This is an "Think outside of the box" type problem.
You may have a bad fuel pressure regulator that is delivering too much fuel pressure to the engine, or the return line from the regulator is plugged causing pressure to backup.
Customer: replied 10 years ago.
We also replaced the fuel pressure regulator. We replaced so many things it is hard to keep track.

Let me ask you this...if you disconnected the wiring at the fuel pump and hooked a test light to it, then turned the key to On. Should the test light come on for 2 seconds then shut off?

If so, then the PCM is not waiting for a signal from the pump and therefore it would not be a pump issue.

Another question...if I push on the Schradder valve when the key is On, and I can hear the fuel pump running, should I get a steady stream of gas? or would there always be presure in the line unless there is a problem with the check valve in the fuel pump?

This is a Double-Expert problem!!
Yes, you should be able to use a test light to see if voltage is getting to the pump when you turn the key on.

As for the valve, there should be residual pressure in the line when you turn the key off IF the check valve at the pump is not leaking.

Pushing the valve to see if there is pressure in the line is NOT a substitute for checking fuel pressure. If the line from the fuel pressure regulator back to the fuel tank is plugged, too much pressure will build up in the fuel system, flooding the engine with fuel preventing it from starting. You need to check fuel pressure with a gauge key on engine off, and if you can get it started with the engine running.
Customer: replied 10 years ago.
Reply to Larry Carley's Post: I disconnected the Inertia switch and turned the key to On, and the fuel pump did not run.

What about this thought....where does the signal come from the ignition (the RPM signal) that tells the PCM the truck is running or not when the key is turned on?

If there is a sensor that looks for the RPM signal, and there is a problem at that sensor, the PCM could be thinking the truck is runing and does not send the signal to the relay to tell it to turn off.
The PCM gets the rpm signal from a crankshaft position sensor mounted on the front of the engine by the crank pulley. It also uses the signal from the cam position sensor to figure out ignition timing and injector sequencing. A bad signal from either coulkd certainly cause a no-start.

Here's the cam sensor, and a location guide for under the hood of your Explorer.

Customer: replied 10 years ago.
Reply to Larry Carley's Post: Do you have a diagram of the location of the crankshaft position sensor?

Are these (somewhat) easy to replace?
The Ford literature does not show it, but it is moutned on the front of the engine by the crank pulley.
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