2003 f150 fuel problem
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New User
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2003 f150 fuel problem
New to this site, my problem is on my 2003 4.6L fuel pump not working.My problem is that I am not getting voltage to contacts on pcm and fuel pump relays.
Getting volts to #30 fuse 30amps ok, voltage to pcm diode ok. Voltage on
#30 on both relays(pcm & fuel) but I am loosing voltage across coils contacts #85 & #86, these makes hot #30 & #87 to make pump work. Inertia sw ok,
Don't know if PCM is bad, ck fuse #2 ok 5 amps, any Ideas?? Thanks
Getting volts to #30 fuse 30amps ok, voltage to pcm diode ok. Voltage on
#30 on both relays(pcm & fuel) but I am loosing voltage across coils contacts #85 & #86, these makes hot #30 & #87 to make pump work. Inertia sw ok,
Don't know if PCM is bad, ck fuse #2 ok 5 amps, any Ideas?? Thanks
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
Time to re-think what should go on, then look again.
Key to Run only powers the PCM.
This in turn causes the PCM to power the pump 'relay' to operate for only a few seconds then stops the pump.
At cranking, the relay and pump are turned on again full time.
This is a two stage operation.
The PCM operates the relay, the relay applies power through the crash sensor to the pump harness from a separate fuse.
Without consulting a set of drawing, I cannot follow your post.
You need to see if the pump relay powers up, if the relay is good, seating an issue etc.
Then which way the power fault lays.
Be sure to press the reset button on the crash sensor so it is set on..
Good luck.
Key to Run only powers the PCM.
This in turn causes the PCM to power the pump 'relay' to operate for only a few seconds then stops the pump.
At cranking, the relay and pump are turned on again full time.
This is a two stage operation.
The PCM operates the relay, the relay applies power through the crash sensor to the pump harness from a separate fuse.
Without consulting a set of drawing, I cannot follow your post.
You need to see if the pump relay powers up, if the relay is good, seating an issue etc.
Then which way the power fault lays.
Be sure to press the reset button on the crash sensor so it is set on..
Good luck.
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New User
Joined: Dec 2016
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Thanks for your response, I have rotated relays around, the only thing that puzzle me, the pcm is powered by #2 fuse 5 amp and its good.From there fuse #30 30amp (good) feats power to pcm diode good, then powers #86 on pcm relay. From there contacts on pcm relay not making to power up fuel pump relay. If pcm is bad then there will be no power to fuse #2 5 amp?? thanks again, I have printed more diagrams and following paths. I keep you in form
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
Fuse F2 does not operate the PCM, it just supplies power to the PCM's KAM so the memory is retained when the key is OFF.
Quite honestly, you aren't reading the diagrams correctly and you don't understand fully how the system operates.
Quite honestly, you aren't reading the diagrams correctly and you don't understand fully how the system operates.
Posting Guru
Joined: Jun 2009
Posts: 1,908
Likes: 20
From: Fort Smith, Arkansas
Set up the multimeter to check power to the pump at the top of the tank.
Have an assistant turn on the key while you are looking at the mulitmeter
because the pump only runs momentarily.
If the engine isn't running, the pump is not fed power. This is the way the system is designed to work.
All the circuit chasing you are doing is more likely to do damage to the PCM because you do not understand how the system works.
Have an assistant turn on the key while you are looking at the mulitmeter
because the pump only runs momentarily.
If the engine isn't running, the pump is not fed power. This is the way the system is designed to work.
All the circuit chasing you are doing is more likely to do damage to the PCM because you do not understand how the system works.
Thread Starter
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New User
Joined: Dec 2016
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Thanks guys, You'll are right ! your inputs are helping me, I am totally diagnosing incorrectly
and don't understand it like I thought.
I will study and re-think diagnosis, retrace diagrams again, and start over. Thanks again
and don't understand it like I thought.
I will study and re-think diagnosis, retrace diagrams again, and start over. Thanks again
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Hotshot
Joined: Jul 2005
Posts: 11,931
Likes: 180
look at the simple first... Volt meter connected to the fuel pump wires. Do you have power when the key is turned on for 3 SECONDS.
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Thread Starter
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New User
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Thanks, I just replace both relays already, I disconnected harness at
fuel pump and check pink/black wire, lights stays on for a few seconds, so power is there., engine start spray works for a few seconds and dies. Next I need to check pressure on fuel rail. Don't have a Ford fitting shraeder (sp) for fuel pressure gage. Pump is new, we have bench test pump it and it worked. I hoping its not a computer so far.
thanks, keep you informed to help others. I have watched
videos, but when problem is not solve the computer is replace.I am making sure to check everything before buying a PCM.
fuel pump and check pink/black wire, lights stays on for a few seconds, so power is there., engine start spray works for a few seconds and dies. Next I need to check pressure on fuel rail. Don't have a Ford fitting shraeder (sp) for fuel pressure gage. Pump is new, we have bench test pump it and it worked. I hoping its not a computer so far.
thanks, keep you informed to help others. I have watched
videos, but when problem is not solve the computer is replace.I am making sure to check everything before buying a PCM.
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
If power comes on at the pink/black wire for the 2-3 seconds and it's full battery voltage (12V+) WITH THE PUMP CONNECTED, there's nothing wrong with the computer or the relays, the problem is rearward in the truck. That means it's either the pump (don't care how new it is or that it bench tested good) or the wiring between the pump and wherever you tested at.
Hotshot
Joined: Jul 2005
Posts: 11,931
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project is right.......... AGAIN, keep it simple... very seldom does the "computer" cause the problem........ many, many pumps/ electrical fail or loose pressure and cause problems. I think getting a pressure reading is your next move.
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
Getting a known-to-be CORRECT voltage reading what's needed. If the voltage reading, when done CORRECTLY is good, there aren't many choices left and either requires either dropping the tank or pulling the bed to pursue.
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New User
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Ok, been testing it with light tester will switch over to Digital Meter, make sure there is no
voltage drop on pump circuit. I will start from pcm relay to fuel then inertia sw to pump, and
see if there is a voltage drop. Yesterday I checked for voltage with light tester on fuel pump
harness, there was voltage but done know if a voltage drop was there. Getting close friends,
have dropped fuel tank before on a older Ford Truck I had.
Your input is helpful, thinking its not the computers. Pump not buzzing at all when key is turned, Voltage to pump is key.
Thanks
voltage drop on pump circuit. I will start from pcm relay to fuel then inertia sw to pump, and
see if there is a voltage drop. Yesterday I checked for voltage with light tester on fuel pump
harness, there was voltage but done know if a voltage drop was there. Getting close friends,
have dropped fuel tank before on a older Ford Truck I had.
Your input is helpful, thinking its not the computers. Pump not buzzing at all when key is turned, Voltage to pump is key.
Thanks
Logistics Pro
Joined: Jan 2001
Posts: 3,740
Likes: 37
From: Central NYS
But don't stop there. Continue on and check for a voltage drop on the ground side. Sometimes the pump may need to run for a while before the ground side voltage drop ramps up.