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1996 Ford F 150 4.9 L6

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7 years 1 week ago #7308 by ScannerDanner

toadyboy1957 wrote: i test all grounds with a VOM or a 12 volt test light from from battery posotive


As long as you are NOT using the ohmmeter. For this type of testing a voltage drop measurement is key, but I do like the test light too.

Don't be a parts changer!
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7 years 1 week ago #7309 by toadyboy1957
Replied by toadyboy1957 on topic 1996 Ford F 150 4.9 L6
i use VOM FOR CONTINUITY testing only

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7 years 1 week ago #7310 by ScannerDanner







If the truck is running fine with the fuel pump relay coil manually grounded, the chances of you having a bad main computer ground are very slim but you should check them anyway.

Don't be a parts changer!
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7 years 1 week ago - 7 years 1 week ago #7311 by ScannerDanner

toadyboy1957 wrote: i use VOM FOR CONTINUITY testing only


You need to stop using the ohmmeter for that. I can give you many examples as to why. Here is the best lesson
www.youtube.com/edit?o=U&video_id=44dP6X3QS5A

Don't be a parts changer!
Last edit: 7 years 1 week ago by ScannerDanner.

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7 years 1 week ago #7313 by toadyboy1957
Replied by toadyboy1957 on topic 1996 Ford F 150 4.9 L6
if im doing something wrong please let me know best way to test all and thanks again

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7 years 1 week ago #7314 by ScannerDanner

toadyboy1957 wrote: if im doing something wrong please let me know best way to test all and thanks again


You're fine man. Use your test light and check those grounds I provided for you.
I am concerned that the driver in the ECM for the fuel pump relay is bad. The question is why? What happened? When did this problem start?
A history would help us here for sure. In the mean time, check those main grounds.

Don't be a parts changer!

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7 years 1 week ago #7315 by toadyboy1957
Replied by toadyboy1957 on topic 1996 Ford F 150 4.9 L6
ive owned the pickup for 7 years about last year i was driving the pickup and for no reason just as i rolled into the driveway the orange blue wire went dead i have no explaination paul

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7 years 1 week ago #7319 by toadyboy1957
Replied by toadyboy1957 on topic 1996 Ford F 150 4.9 L6
inside the PCM do you know if the fuel pump driver travels through a directional capacitor FROM THE ORANGE BLUE WIRE going into the PCM or where and how does it obtain its ground??

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7 years 1 week ago #7320 by ScannerDanner

toadyboy1957 wrote: inside the PCM do you know if the fuel pump driver travels through a directional capacitor FROM THE ORANGE BLUE WIRE going into the PCM or where and how does it obtain its ground??


It is a switched ground. The ECM is using a transistor to switch the fuel pump relay coil on and off and it is based on two main inputs.
#1 an ignition feed that powers up the computer
#2 an RPM signal

When the computer first is powered up by the ignition, it will turn that driver (transistor) on for 1-2 seconds. This is your prime.
After that, the PIP signal is your RPM input and as long as it is there, the ECM will keep that relay circuit turned on.

The fact that you have injector pulse tells us this PIP signal is good.

Where does it ground? To the board itself. Where does the board ground? To those wires I highlighted in this thread

Don't be a parts changer!
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7 years 1 week ago #7321 by toadyboy1957
Replied by toadyboy1957 on topic 1996 Ford F 150 4.9 L6
youre correct PAUL the PIP HAS FULL SIGNAL otherwise when i provide the fuel pump relay a ground the engine would never run and i will continue chasong grounds thank you and God Bless You Paul

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7 years 1 week ago #7430 by toadyboy1957
Replied by toadyboy1957 on topic 1996 Ford F 150 4.9 L6
Ok / I ran all the grounds / backprobed all the grounds at the PCM WITH TEST LIGHT on battery posotive . all GROUNDS are present but still HAVE NO GROUNDS AT O2 SENSORS OR SOLENOIDS. IAC,MAF IAT DPFE CRK SENSORS ALL IGNITION SYSTEM MAIN PCM DIODE PCM FUSES RELAYS ALL POWER UP FINE.. I also have a direct short in fuse 16 in the underdash FUSEBOX can you help me with the color wire and any connections so i can trace this down im not sure if this has anything to do with the grounds or not this thing is becoming a nightmare LOL

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7 years 1 week ago #7465 by Tyler
Replied by Tyler on topic 1996 Ford F 150 4.9 L6

toadyboy1957 wrote: Ok / I ran all the grounds / backprobed all the grounds at the PCM WITH TEST LIGHT on battery posotive . all GROUNDS are present but still HAVE NO GROUNDS AT O2 SENSORS OR SOLENOIDS. IAC,MAF IAT DPFE CRK SENSORS ALL IGNITION SYSTEM MAIN PCM DIODE PCM FUSES RELAYS ALL POWER UP FINE.. I also have a direct short in fuse 16 in the underdash FUSEBOX can you help me with the color wire and any connections so i can trace this down im not sure if this has anything to do with the grounds or not this thing is becoming a nightmare LOL


Fuse 16? Shorted, as in it pops a fuse as soon as it's installed? Lemme grab the I/P fuse box diagram.



For the record, I hate how the OE Ford diagrams combine underhood and underdash fuse boxes in the same diagram at times. :lol: Finally found fuse 16:



Not related to your other issues, unfortunately. :( If you wanted to chase this short, I'd probably start with unplugging the cigar lighter and recheck for the short. If that didn't work, then you can follow the light blue/white wire for a short to ground.

Back to your PCM... Sure is sounding like a bad engine computer to me. :unsure:
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7 years 1 week ago #7466 by toadyboy1957
Replied by toadyboy1957 on topic 1996 Ford F 150 4.9 L6
what would cause the fuel pump driver to just suddenly stop working ??i have no idea how long all the grounds to the other items have been dead>> and again thanks for all your assistance and wiring diagrams have been of great help

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7 years 1 week ago #7469 by toadyboy1957
Replied by toadyboy1957 on topic 1996 Ford F 150 4.9 L6
and do the o2 sensor grounds come from inside the PCM OR AN external ground??

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7 years 1 week ago #7471 by toadyboy1957
Replied by toadyboy1957 on topic 1996 Ford F 150 4.9 L6
even tho the cigar lighter is unplugged and isolated it still pops fuses soon as i install a new 1

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7 years 1 week ago #7476 by Tyler
Replied by Tyler on topic 1996 Ford F 150 4.9 L6

toadyboy1957 wrote: even tho the cigar lighter is unplugged and isolated it still pops fuses soon as i install a new 1


Ah crap, I'm sorry man, that was the easy test first. :( You're down to a direct short now. My go-to test for this kind of thing is to leave the cigar lighter disconnected, and use a test light connected to B+ on the light blue/white wire at the lighter connector. Trace the harness, wiggling carefully as you go, and keep an eye on the test light. When you move the short off of ground, the test light will flicker/go out.

and do the o2 sensor grounds come from inside the PCM OR AN external ground??


These get a ground inside the PCM:



It's worth noting here that, without the engine running, the PCM may not ground the O2 heaters. It may only ground the heaters once the engine is running.

Does the IAC have a ground when cranking? That'd tell us the PCM has the capability of controlling at least one of it's outputs.
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7 years 1 week ago #7480 by toadyboy1957
Replied by toadyboy1957 on topic 1996 Ford F 150 4.9 L6
IAC,MAF IAT DPFE CRK SENSORS ALL IGNITION SYSTEM MAIN PCM DIODE PCM FUSES RELAYS ALL POWER UP FINE and all lights internal and external all work properly

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7 years 1 week ago #7482 by toadyboy1957
Replied by toadyboy1957 on topic 1996 Ford F 150 4.9 L6
the engine starts and runs fine with a self provided ground to the fuel pump relay where the lt/blue - orange wire plugs in on the relay thats the fuel pump control wire going into the pcm

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7 years 1 week ago #7486 by Tyler
Replied by Tyler on topic 1996 Ford F 150 4.9 L6

toadyboy1957 wrote: the engine starts and runs fine with a self provided ground to the fuel pump relay where the lt/blue - orange wire plugs in on the relay thats the fuel pump control wire going into the pcm


If everything else works, then I think you're looking at a simple failed driver OR there was a short to power on the light blue/orange wire, either from a wiring problem, or a shorted relay coil. Either way, it seems like the damage has been done.

Have you tried driving around with the fuel pump relay control jumped? Ran well? Honestly, if this was my truck, I'd be REALLY tempted to wire a rocker switch into that light blue/orange wire and put it on the dash. :whistle: You could even hide it somewhere, and now you've got a cheap anti-theft system! :lol:

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7 years 1 week ago #7489 by borntoroll
Replied by borntoroll on topic 1996 Ford F 150 4.9 L6
And not to forget to check current travelling through this "jumper"

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