How JustAnswer Works:

  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.

Ask Larry Your Own Question

Larry
Larry, Technical Editor
Category: Ford
Satisfied Customers: 1139
Experience:  Automotive tech editor & author, 30 years experience, ASE certified
4265081
Type Your Ford Question Here...
Larry is online now
A new question is answered every 9 seconds

Fuel pump..the PCM module, ignition control module, fuel filter..sits

Resolved Question:

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?
Submitted: 7 years ago.
Category: Ford
Expert:  Larry replied 7 years ago.
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.

graphic

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

OPERATION
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 7 years ago.
Reply to Larry Carley's Post: I forgot to add that I have also replaced the fuel pump relay.
Expert:  Larry replied 7 years ago.
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 7 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 run...no 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?
Expert:  Larry replied 7 years ago.
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 7 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 fine...no 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.
Expert:  Larry replied 7 years ago.
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 7 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!!
Expert:  Larry replied 7 years ago.
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 7 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.
Expert:  Larry replied 7 years ago.
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.

graphicgraphic
Customer: replied 7 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?
Expert:  Larry replied 7 years ago.
The Ford literature does not show it, but it is moutned on the front of the engine by the crank pulley.
Larry, Technical Editor
Category: Ford
Satisfied Customers: 1139
Experience: Automotive tech editor & author, 30 years experience, ASE certified
Larry and 10 other Ford Specialists are ready to help you

JustAnswer in the News:

 
 
 
Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.
 
 
 

What Customers are Saying:

 
 
 
  • AlvinC answered a question about my Ford truck that only someone with an in-depth knowledge of his subject would have known what was going on. Rich D USA
< Last | Next >
  • AlvinC answered a question about my Ford truck that only someone with an in-depth knowledge of his subject would have known what was going on. Rich D USA
  • Because of your expertise, you armed me with enough ammunition to win the battle with the dealer. They are installing a fuel filter and fuel pump at no charge to me. Molly USA
  • I needed help with my car on Saturday morning....got a response in 5 minutes, and it was the perfect solution. Thanks again to your service. Jason V. Kirkland, WA
  • I do know, after going though this with JustAnswer, that I can somewhat trust my mechanic but I will always contact you prior to going there. BR New Jersey
  • I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry. Stephanie P Elm City, NC
  • used your service this weekend with "Trecers" help. thank you ,thank you, thank you. replaced an A/C fan motor. Local Auto Zone had part. $15.00 "tracer" fee and $40.00 for parts, I saved several hundreds of dollers at a shop. i will recommend you and use you in the future. David L. Richmond, TX
  • 9 dollars, 2 hours of my time, and I drove away. Your diagnosis was right on the mark. Thank you so much. Phil Marysville, CA
 
 
 

Meet The Experts:

 
 
 
  • Ron

    ASE Certified Technician

    Satisfied Customers:

    20942
    23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
< Last | Next >
  • http://ww2.justanswer.com/uploads/FO/fordguy4u/2011-12-17_222940_HPIM1257.64x64.JPG Ron's Avatar

    Ron

    ASE Certified Technician

    Satisfied Customers:

    20942
    23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
  • http://ww2.justanswer.com/uploads/MU/muddyford/2012-6-13_1204_1.64x64.png Chris (aka- Moose)'s Avatar

    Chris (aka- Moose)

    Ford Technician

    Satisfied Customers:

    22382
    16 years experience with Ford.
  • http://ww2.justanswer.com/uploads/JM/jmcdo28/2012-2-23_01655_resized.64x64.jpg John Mc's Avatar

    John Mc

    Ford Technician

    Satisfied Customers:

    5493
    19 years Ford Lincoln Mercury experience
  • http://ww2.justanswer.com/uploads/wmarti7/2009-4-18_04332_Avatar.jpg Chuck's Avatar

    Chuck

    ASE Certified Technician

    Satisfied Customers:

    1684
    33 Years Experience,Ford Senior Master,ASE Master,L1 Advanced Engine Performance
  • http://ww2.justanswer.com/uploads/CR/crzydrvr00/2013-11-3_12123_246347.64x64.jpg Richard's Avatar

    Richard

    ASE Certified Technician

    Satisfied Customers:

    1518
    12 years at a Ford Lincoln/Mercury and Jaguar dealer as a technician and shop foreman.
  • http://ww2.justanswer.com/uploads/BA/baddad1/2014-4-1_23659_avatar.64x64.jpg Mike V.'s Avatar

    Mike V.

    Auto Service Technician

    Satisfied Customers:

    789
    25 years experience on all makes and models, Licensed NYS Inspector.
  • http://ww2.justanswer.com/uploads/lostrider/2009-9-26_23144_php4VNWAA_c1PM1.jpg lostrider's Avatar

    lostrider

    Ford Technician

    Satisfied Customers:

    2940
    ASE Master Technician, Ford Senior Master Technician,Diesel certified, ASE Master, 22 yrs FORD exp.