Changing fuel pump, what else needs changing?
Thread Starter
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Mountain Pass
Joined: Feb 2016
Posts: 150
Likes: 1
From: Los Angeles
Changing fuel pump, what else needs changing?
UPDATE: Truck is fixed, thanks!!! See post 12 below.
2001 V10 CCLB 4x4, fuel pump quit. Quit on the road and it wasn't the reset switch. Checked fuses.
I'm about to order a new Motorcraft pump assembly. Is there anything else that I need to change? Does the new assembly come with a new gasket?
Any other advice is appreciated.
2001 V10 CCLB 4x4, fuel pump quit. Quit on the road and it wasn't the reset switch. Checked fuses.
I'm about to order a new Motorcraft pump assembly. Is there anything else that I need to change? Does the new assembly come with a new gasket?
Any other advice is appreciated.
Fleet Mechanic
Joined: Feb 2011
Posts: 1,812
Likes: 88
From: Thousand Oaks, CA
If you're getting 12v at the Inertia Switch the relay is probably good.
Last edited by R&T Babich; Sep 24, 2017 at 09:50 PM. Reason: More general test
Thread Starter
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Mountain Pass
Joined: Feb 2016
Posts: 150
Likes: 1
From: Los Angeles
I didn't test the inertia switch for 12v. It just wasn't tripped.
EDIT: Just checked inertia switch and getting 12volts when the key first is turned to ON, then it drops to 6.8 volts and stays there. Still don't know where the fuel pump relay is.
Fleet Mechanic
Joined: Feb 2011
Posts: 1,812
Likes: 88
From: Thousand Oaks, CA
Seems odd, there should be a fuel pump relay somewhere.
The fuel pump is turned on for a few seconds when the ignition switch is turned to Run to prime the lines, then shut down. When the ignition switch is turned to Start the PCM looks at several other inputs and fires up the fuel pump to run the engine when everything is good to go. With the engine running the voltage at the Inertia Switch should be system voltage or around 13.4v. I added a voltmeter on the dash and tapped the Inertia Switch output lead for the source. The voltage is usually around 13.2-13.5v or when the battery is low can go up around 14.2v when the engine is running.
When do you see the 6.8v? When the engine is running? That would barely be enough to run the fuel pump or not.
For a test you could run a new wire from the battery to the Inertia Switch.
Thread Starter
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Mountain Pass
Joined: Feb 2016
Posts: 150
Likes: 1
From: Los Angeles
Engine does not run. Engine quit while driving and hasn't started since. I had it towed home.
I put the multimeter on all 3 wires going into the inertia switch. Only one shows any voltage.
key off = 0 volts
key on = momentary 12v, then steady 6.8v after that
when I say 12v that's literally what the meter reads 12.0 volts. Battery at the terminals is currently 12.4v. I just put it on a charger. I think I drained it a little testing on the road side.
I put the multimeter on all 3 wires going into the inertia switch. Only one shows any voltage.
key off = 0 volts
key on = momentary 12v, then steady 6.8v after that
when I say 12v that's literally what the meter reads 12.0 volts. Battery at the terminals is currently 12.4v. I just put it on a charger. I think I drained it a little testing on the road side.
Fleet Mechanic
Joined: Feb 2011
Posts: 1,812
Likes: 88
From: Thousand Oaks, CA
With a good fuel pump there should be pressure in the rail, 32+ psi.
Elder User
Joined: Jul 2015
Posts: 584
Likes: 1
It sounds like his pump wiring is working, the voltage will go down until the engine begins cranking and then it will come back up. I would just replace the pump.
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Fleet Mechanic
Joined: Feb 2011
Posts: 1,812
Likes: 88
From: Thousand Oaks, CA
If the voltage is going to 6.8v while cranking that is too low for the electronics to work, should be at least 9.5v while cranking.
If the fuel pressure is good at initial turn on the pump does work, but doesn't mean it will hold pressure while running.
We need more info on the fuel pressure.
If the contacts in the relay are burned you might get enough power thru it to prime the rails, but may not allow enough current thru to maintain volume while running.
A test lead from the battery to the Inertia Switch or all the way back to the pump would help a lot.
I think it's probably the pump, but I've read posts from several people that have changed pumps only to have the problem be the relay.
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Elder User
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The voltage going to 6.8v is strange, it should go to zero or near zero.
If the voltage is going to 6.8v while cranking that is too low for the electronics to work, should be at least 9.5v while cranking.
If the fuel pressure is good at initial turn on the pump does work, but doesn't mean it will hold pressure while running.
We need more info on the fuel pressure.
If the contacts in the relay are burned you might get enough power thru it to prime the rails, but may not allow enough current thru to maintain volume while running.
A test lead from the battery to the Inertia Switch or all the way back to the pump would help a lot.
I think it's probably the pump, but I've read posts from several people that have changed pumps only to have the problem be the relay.
If the voltage is going to 6.8v while cranking that is too low for the electronics to work, should be at least 9.5v while cranking.
If the fuel pressure is good at initial turn on the pump does work, but doesn't mean it will hold pressure while running.
We need more info on the fuel pressure.
If the contacts in the relay are burned you might get enough power thru it to prime the rails, but may not allow enough current thru to maintain volume while running.
A test lead from the battery to the Inertia Switch or all the way back to the pump would help a lot.
I think it's probably the pump, but I've read posts from several people that have changed pumps only to have the problem be the relay.
Thread Starter
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Mountain Pass
Joined: Feb 2016
Posts: 150
Likes: 1
From: Los Angeles
Engine cranks but not even a hint of it going to fire. It just cranks and cranks.
I will test it again when I get home as you suggest. I haven't tried to see what voltage does while cranking. I just checked it in the on position.
Lead Driver
Joined: Nov 2008
Posts: 8,449
Likes: 70
From: South Jersey
Gas tank rubber vent lines, had my bed off the other day to wire wheel and repaint the frame and the hoses that I replaced three years ago were all flaking apart and crumbling. Looks like I'll have to add it to my yearly routine
Thread Starter
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Mountain Pass
Joined: Feb 2016
Posts: 150
Likes: 1
From: Los Angeles
UPDATE: Truck is fixed
I replaced the fuel pump today and it's running. I also changed the rubber vent hoses as they were disintegrating. Thanks for all the help.
It was a tough job solo, in the street where the tow truck left me. It took me about 5 hours I figure.
I replaced the fuel pump today and it's running. I also changed the rubber vent hoses as they were disintegrating. Thanks for all the help.
It was a tough job solo, in the street where the tow truck left me. It took me about 5 hours I figure.
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