Fuel delivery issue...
Thread Starter
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Senior User
Joined: Jun 2013
Posts: 107
Likes: 9
From: Valley Mills, TX
Fuel delivery issue...
Im not much for long stories so here are the facts
1993 F150 extd cab 4x4 5.8 (351) V8
-Truck was driving today
-fuel Cut off on the interstate and towed home
-tested all the fuses and relays (PCM and fuel pump relays) all seem to be working (clicking)
-inertia switch is not tripped
-Have power to sending unit
-No power to fuel pump (either front or rear)
-check codes I am getting 542
Questions:
can the relays be bad even though they seem to be clicking?
Please include diagrams or crude paint pictures if your suggestions include chasing wires as I don't have any books or literature on this truck. Any help is greatly appricated.
1993 F150 extd cab 4x4 5.8 (351) V8
-Truck was driving today
-fuel Cut off on the interstate and towed home
-tested all the fuses and relays (PCM and fuel pump relays) all seem to be working (clicking)
-inertia switch is not tripped
-Have power to sending unit
-No power to fuel pump (either front or rear)
-check codes I am getting 542
Questions:
can the relays be bad even though they seem to be clicking?
Please include diagrams or crude paint pictures if your suggestions include chasing wires as I don't have any books or literature on this truck. Any help is greatly appricated.
Fleet Owner
Joined: Aug 2005
Posts: 23,667
Likes: 301
From: Easton,Ks
You can swap the relays with the horn relay for testing, they are the same.
If you have gauge power to the sending unit and no power at the pumps and have power at the inertia switch then you have most likely a bad selector switch mounted on the dash.
I would dough the relays are bad but as I said above if they toot in the horn position then they are good.
That said for your information the power will only be on the fuel pumps for one second each time the key is turned to the run position if the the engine is not cranking or running.
You most likely have an Ignition problem and you need to check for spark when the engine does not run. If no spark the most likely candidate is the PIP sensor inside the distributor. The PIP sensor can also cause the fuel pumps not to run while cranking.
To check the running condition of the fuel system with a test light just ground pin #6 of the self-test plug and turn on the key or short pin #2 to pin #6 and turn on the key.
Self-Test plug location:
/
If you have gauge power to the sending unit and no power at the pumps and have power at the inertia switch then you have most likely a bad selector switch mounted on the dash.
I would dough the relays are bad but as I said above if they toot in the horn position then they are good.
That said for your information the power will only be on the fuel pumps for one second each time the key is turned to the run position if the the engine is not cranking or running.
You most likely have an Ignition problem and you need to check for spark when the engine does not run. If no spark the most likely candidate is the PIP sensor inside the distributor. The PIP sensor can also cause the fuel pumps not to run while cranking.
To check the running condition of the fuel system with a test light just ground pin #6 of the self-test plug and turn on the key or short pin #2 to pin #6 and turn on the key.
Self-Test plug location:
/
Thread Starter
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Senior User
Joined: Jun 2013
Posts: 107
Likes: 9
From: Valley Mills, TX
Ok subford I did every thing you said. and have some new information
I just went out there this morning and started from scratch:
selector switch front-no jumper-key on : nothing
selector switch back-no jumper-key on : hear the back pump prime
selector switch front-jumper from pin 2 to 6-key on : nothing
selector switch front-pin six grounded with test light-key on : nothing
selector switch back-jumper from pin 2 to 6-key on : good prime
selector switch back-pin 6 grounded w/ test light-key on : good prime
Tested all relays in the horn position and got a beep out of all of them
So you might be saying to yourself, sweet so just run off of the rear tank but here's the problem the rear tank seems to be feeding into and over-filling/over-pressurizing the front cause I know I had fuel in that rear tank and now its empty. and my front was about half and it is full. so now my problem is 2 fold
1. Why is the rear tank pumping into the front and how do I fix it?
2. Does it sound like my selector switch is bad since everything works in back but not front?
I just went out there this morning and started from scratch:
selector switch front-no jumper-key on : nothing
selector switch back-no jumper-key on : hear the back pump prime
selector switch front-jumper from pin 2 to 6-key on : nothing
selector switch front-pin six grounded with test light-key on : nothing
selector switch back-jumper from pin 2 to 6-key on : good prime
selector switch back-pin 6 grounded w/ test light-key on : good prime
Tested all relays in the horn position and got a beep out of all of them
So you might be saying to yourself, sweet so just run off of the rear tank but here's the problem the rear tank seems to be feeding into and over-filling/over-pressurizing the front cause I know I had fuel in that rear tank and now its empty. and my front was about half and it is full. so now my problem is 2 fold
1. Why is the rear tank pumping into the front and how do I fix it?
2. Does it sound like my selector switch is bad since everything works in back but not front?
Logistics Pro
Joined: Mar 2005
Posts: 4,698
Likes: 47
From: Mexico, Missouri
Rear pump is bad.
The selector switch may or may not be bad since it usually fails completely. You can remove the bezel/dash and then remove the switch. Carbon is sometimes the culprit since its electrical and try to clean it.
May need to hit the junkyard for a spare as a backup as they are plastic and are known to break and the plastic is old and been through many hot/cold cycles.
The selector switch may or may not be bad since it usually fails completely. You can remove the bezel/dash and then remove the switch. Carbon is sometimes the culprit since its electrical and try to clean it.
May need to hit the junkyard for a spare as a backup as they are plastic and are known to break and the plastic is old and been through many hot/cold cycles.
Thread Starter
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Senior User
Joined: Jun 2013
Posts: 107
Likes: 9
From: Valley Mills, TX
More info
reading selector switch wires with the test light
switch front-key on-test light on pin 6 (red): Nothing
switch back-key on-test light on pin 4 (brn/w): good power
reading selector switch wires with the test light
switch front-key on-test light on pin 6 (red): Nothing
switch back-key on-test light on pin 4 (brn/w): good power
Lead Driver
Joined: Aug 2006
Posts: 5,670
Likes: 13
From: Sand Lake, MI
Repeat the test but with the selector switch unplugged, jumper from R/Y wire to R wire across at the switch connector, if the front tank pump runs the switch is the problem if not suggests the pump as the problem.
Thread Starter
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Senior User
Joined: Jun 2013
Posts: 107
Likes: 9
From: Valley Mills, TX
Thanks Danr1 I finally did narrow it down to the switch
I was going out to run the test you suggested and saw some lawn care guys with a OBS f150 so I went over and asked them if I could borrow their fuel selector switch. after a couple wierd looks and a little more explaining I transplanted their switch onto my truck and POOF all is right in the world again.
So i have already purchased a new pump but I have yet to install it. pertaining to my cross fueling issue, I have read that this is cause by a worn out pump, is this true? if so Ill go ahead and put in the new one if not I wanna get my money back.
I was going out to run the test you suggested and saw some lawn care guys with a OBS f150 so I went over and asked them if I could borrow their fuel selector switch. after a couple wierd looks and a little more explaining I transplanted their switch onto my truck and POOF all is right in the world again.
So i have already purchased a new pump but I have yet to install it. pertaining to my cross fueling issue, I have read that this is cause by a worn out pump, is this true? if so Ill go ahead and put in the new one if not I wanna get my money back.
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Lead Driver
Joined: Aug 2006
Posts: 5,670
Likes: 13
From: Sand Lake, MI
Yea you corrected the power to the front tank issue but sadly because of the fuel transfer issue with it you're gonna have to pull the front pump anyway.
With the fuel transfer issue the receiving tank is the problem tank, fuel transfer from rear to front tank means the front tank's FMU is faulty.
With the fuel transfer issue the receiving tank is the problem tank, fuel transfer from rear to front tank means the front tank's FMU is faulty.
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Elder User
Joined: Feb 2013
Posts: 856
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From: Livonia, MI
PS - I believe there was a recall on the '93 F-150 and an external valve was installed by the dealer right at the tank. Might want to check and see if the previous owner took advantage of the recall.
Thread Starter
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Senior User
Joined: Jun 2013
Posts: 107
Likes: 9
From: Valley Mills, TX
ok so just to be clear:
My truck is dumping fuel from rear to front so replacing the front fuel pump will solve this issue?
I currently have the bed of the truck (way better than dropping the tanks BTW!) so I wanna make sure I address all issues
My truck is dumping fuel from rear to front so replacing the front fuel pump will solve this issue?
I currently have the bed of the truck (way better than dropping the tanks BTW!) so I wanna make sure I address all issues
Logistics Pro
Joined: Mar 2005
Posts: 4,698
Likes: 47
From: Mexico, Missouri
Rear pump is bad.
Shuttle valve has gone bad in the pump.
Edit, I always get this wrong on which pump.
Others are right. My apologies. Sometimes no advice is better than bad advice. I need to leave a note for myself regarding which is bad for the cross fueling problem even though I've been through it already.
Shuttle valve has gone bad in the pump.
Edit, I always get this wrong on which pump.
Others are right. My apologies. Sometimes no advice is better than bad advice. I need to leave a note for myself regarding which is bad for the cross fueling problem even though I've been through it already.
Thread Starter
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Senior User
Joined: Jun 2013
Posts: 107
Likes: 9
From: Valley Mills, TX
Thank ya'll so much, this is why the first thing I do when I buy a new vehicle is find the appropriate forum, so many previous lessons learned and knowledge out there. without this forum i would probably still be attempting to drop the fuel tank(s) instead of putting everything back together.
More Turbo
Joined: Mar 2003
Posts: 665
Likes: 6
From: Detroit suburb
So, if one were inclined to attempt to determine if the check valve or shuttle valve is faulty, has that been done, or a write up or perhaps a you tube posting of this, if anyone knows ? That could be a substantial cost savings if a relatively easy fix ....