94 150 Fuel delivery issues
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5th Wheeling
Joined: Jan 2024
Posts: 42
Likes: 5
From: Durham
94 150 Fuel delivery issues
A riddle for Thursday.
1994 F150 XL 5.0
Went out the other morning, truck would crank but would not start. There is at least 1/2 tank of fuel in both tanks.
Checked fuses, fine.
I noticed that when putting ignition to ON position, there was no noise from either front or rear fuel pump, when normally they make noise (when priming?).
I hooked up a jumper wire to the testing plug as if I were going to do a fuel pressure test. Turned key to ON position which should turn on the fuel pump. Nothing from either front or rear.
I just put in a new fuel pump relay this morning in the correct position. Front fuel tank, nothing, crank and no start. Rear fuel tank, this time it cranked a bit and actually started, but ran very rough and would die if I didn't give it a little gas. Similarly, if I gave it more gas, it would also die.
Front fuel pump was making louder than normal noise last week... so could it have been on it's way out? Regardless if it died, shouldn't there be no issues running with rear?
Ok I'm at a loss of what to check next, any suggestions would be greatly appreciated.
Bill
1994 F150 XL 5.0
Went out the other morning, truck would crank but would not start. There is at least 1/2 tank of fuel in both tanks.
Checked fuses, fine.
I noticed that when putting ignition to ON position, there was no noise from either front or rear fuel pump, when normally they make noise (when priming?).
I hooked up a jumper wire to the testing plug as if I were going to do a fuel pressure test. Turned key to ON position which should turn on the fuel pump. Nothing from either front or rear.
I just put in a new fuel pump relay this morning in the correct position. Front fuel tank, nothing, crank and no start. Rear fuel tank, this time it cranked a bit and actually started, but ran very rough and would die if I didn't give it a little gas. Similarly, if I gave it more gas, it would also die.
Front fuel pump was making louder than normal noise last week... so could it have been on it's way out? Regardless if it died, shouldn't there be no issues running with rear?
Ok I'm at a loss of what to check next, any suggestions would be greatly appreciated.
Bill
Logistics Pro
Joined: Nov 2013
Posts: 3,928
Likes: 1,198
From: Mojave, Ca
Here is the fuel pump wiring diagram. The fuel selector switch and the inertia switch are both parts that rarely fail, but can cause the symptoms you're experiencing. You can temporarily jump the terminals with a paper clip to see if the fuel pumps start running to diagnose the failed part.
The fuel pump ground terminal is near the drivers side head light and that may be a problem too. Make sure the wire isn't 'stretchy' as that indicates a broken wire inside the plastic insulation.
Thread Starter
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5th Wheeling
Joined: Jan 2024
Posts: 42
Likes: 5
From: Durham
Thank you for this info, this is really helpful. I'll look this over.
Separatley and more just out of curiosity, I pulled the PCM out and found that the case is very corroded and rusty. I have not yet opened it up to look for any burnt resistors yet, but will later today. I understand that if there are issues with the PCM that doesn't mean there may not be issues in other areas of the circuit as well.
I'm hoping it's not the fuel tank selector switch as I replaced that about 6 months ago. but I'll check.
thanks again.
Separatley and more just out of curiosity, I pulled the PCM out and found that the case is very corroded and rusty. I have not yet opened it up to look for any burnt resistors yet, but will later today. I understand that if there are issues with the PCM that doesn't mean there may not be issues in other areas of the circuit as well.
I'm hoping it's not the fuel tank selector switch as I replaced that about 6 months ago. but I'll check.
thanks again.
Logistics Pro
Joined: Nov 2013
Posts: 3,928
Likes: 1,198
From: Mojave, Ca
Thank you for this info, this is really helpful. I'll look this over.
Separatley and more just out of curiosity, I pulled the PCM out and found that the case is very corroded and rusty. I have not yet opened it up to look for any burnt resistors yet, but will later today. I understand that if there are issues with the PCM that doesn't mean there may not be issues in other areas of the circuit as well.
I'm hoping it's not the fuel tank selector switch as I replaced that about 6 months ago. but I'll check.
thanks again.
Separatley and more just out of curiosity, I pulled the PCM out and found that the case is very corroded and rusty. I have not yet opened it up to look for any burnt resistors yet, but will later today. I understand that if there are issues with the PCM that doesn't mean there may not be issues in other areas of the circuit as well.
I'm hoping it's not the fuel tank selector switch as I replaced that about 6 months ago. but I'll check.
thanks again.
Thread Starter
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5th Wheeling
Joined: Jan 2024
Posts: 42
Likes: 5
From: Durham
Thank you all for comments and help. Prototypemech, thanks for the diagrams... it really helped. Ended up being the fuel tank selector switch apparently went bad.
UPDATE:
PCM actually looked fairly clean inside even though really rusty corroded outside. I reinstalled it. And it was good learning from your comments that I already jumped that circuit, so that should not have been the issue.
Went to the inertia switch and it was not tripped. I manually put the button in the tripped position, lifting it with a flathead screwdriver, then reset it. Not sure if that did anything, but it made me feel better.
Then removed fuel tank selector switch. Ran a paperclip from 12v power pin hole to front fuel pump pin hole. Turned key to ON position and got priming noise. Did same with rear fuel pump and also got priming noise.
Replaced fuel tank selector switch with new one and truck fired right up, both front and rear tanks.
Frustrating because the fuel level was showing correctly with the fuel tank selector switch, it just wasn't powering the fuel pumps. I also just purchased that switch in Jan or Feb.
Anyway, I'll update again if anything further, but now I have to go put everything back together.
Cheers.
UPDATE:
PCM actually looked fairly clean inside even though really rusty corroded outside. I reinstalled it. And it was good learning from your comments that I already jumped that circuit, so that should not have been the issue.
Went to the inertia switch and it was not tripped. I manually put the button in the tripped position, lifting it with a flathead screwdriver, then reset it. Not sure if that did anything, but it made me feel better.
Then removed fuel tank selector switch. Ran a paperclip from 12v power pin hole to front fuel pump pin hole. Turned key to ON position and got priming noise. Did same with rear fuel pump and also got priming noise.
Replaced fuel tank selector switch with new one and truck fired right up, both front and rear tanks.
Frustrating because the fuel level was showing correctly with the fuel tank selector switch, it just wasn't powering the fuel pumps. I also just purchased that switch in Jan or Feb.
Anyway, I'll update again if anything further, but now I have to go put everything back together.
Cheers.
Mountain Pass
Joined: Jun 2024
Posts: 163
Likes: 15
"The fuel pump ground terminal is near the drivers side head light". Not to hijack, but (a) why is the ground for the fuel pump so far away from the fuel pump, and (b) is the same ground used for the sender as the pump itself? My pump works, but the gauge always reads empty, just on the front tank. Probably sender itself, but it would sure be nice if it was just a ground someplace.
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Cross-Country
Joined: Aug 2011
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From: South Puget Sound
"The fuel pump ground terminal is near the drivers side head light". Not to hijack, but (a) why is the ground for the fuel pump so far away from the fuel pump, and (b) is the same ground used for the sender as the pump itself? My pump works, but the gauge always reads empty, just on the front tank. Probably sender itself, but it would sure be nice if it was just a ground someplace.
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Logistics Pro
Joined: Nov 2013
Posts: 3,928
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From: Mojave, Ca
"The fuel pump ground terminal is near the drivers side head light". Not to hijack, but (a) why is the ground for the fuel pump so far away from the fuel pump, and (b) is the same ground used for the sender as the pump itself? My pump works, but the gauge always reads empty, just on the front tank. Probably sender itself, but it would sure be nice if it was just a ground someplace.
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