SOLVED: Fuel system electrical diag road block


ecgreen

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OK, jumping did nothing. Relay is good. Put a new one in just to see.

I am getting 11.5 volts when I measure voltage on the pink/black (hot) and black wires (ground) on the pump connector.

Did a test:
- I took an old pump and held a wire to the red and black terminals and hooked it up to a battery, the pump fired up.
- Hooked up the verified pump to the pump connector on the truck, turned the key and nothing - the pump did not run.
- I even measured voltage on the red and black wires on the sending unit. Nothing there

So I am not understanding how this pump works. There are four pins on the connector. One is power, onen is ground (both of those work). So the other wires must have something to do with letting that power into the pump unit (and whatever that connection is, that should be the problem). Those two wires must also have something to do with shutting off the pump after 2 seconds, right? The diagram says the orange goes to the same ground as the black wire, but what does the Y/W do? Whatever is wrong with those two wires, is stopping the voltage from going through the pins on the pump hanger and into the wires connected to those pins.

Please be patient with this thick headed man.
 


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ericbphoto

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The y/w and orange wires are for the sending unit (fuel level sensor). They have nothing to do with power to the pump.
 

farmer

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OK, jumping did nothing. Relay is good. Put a new one in just to see.

I am getting 11.5 volts when I measure voltage on the pink/black (hot) and black wires (ground) on the pump connector.

Did a test:
- I took an old pump and held a wire to the red and black terminals and hooked it up to a battery, the pump fired up.
- Hooked up the verified pump to the pump connector on the truck, turned the key and nothing - the pump did not run.
- I even measured voltage on the red and black wires on the sending unit. Nothing there

So I am not understanding how this pump works. There are four pins on the connector. One is power, onen is ground (both of those work). So the other wires must have something to do with letting that power into the pump unit (and whatever that connection is, that should be the problem). Those two wires must also have something to do with shutting off the pump after 2 seconds, right? The diagram says the orange goes to the same ground as the black wire, but what does the Y/W do? Whatever is wrong with those two wires, is stopping the voltage from going through the pins on the pump hanger and into the wires connected to those pins.

Please be patient with this thick headed man.
Change the pump.

One of the extra wires is for the fuel gauge, maybe both, idk not looking at a diagram
 

alwaysFlOoReD

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I can't see any info under your avatar as I'm on mobile.
Is this a frame rail pump?
Don't forget the pcm shuts off power to the pump after 2 seconds if the engine isn't running.
You can jumper at the obd1 connector to turn the pump on continuously. Look in the tech section for instructions.
If its a frame rail pump there is a short pig tail that connects to the frame side wiring. That pigtail connects to the pump under rubber boots. Those connections have been loose on every pump I've looked at. Crimp new ends on if that's what you have.
 

ecgreen

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Change the pump.

One of the extra wires is for the fuel gauge, maybe both, idk not looking at a diagram
I dunno, I have tried two pumps, both of which I verified working outside of the vehicle
 

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Did you check the ground at the pump? If you have 11.5 volts there and the pumps run outside the vehicle, I would suspect the ground. Connect the pump at the frame, and install the jumper like alwaysfloored said. If the pump doesn't run, run a ground straight from the battery to the pump and try that. I mean, a fresh ground and/or hot straight from the battery has to work. That way you can determine if the positive or negative (or both) feeding the pumps are the problem or not.
 

ecgreen

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OK I jumped the ground off of the obd to the battery and the pump ran. So the issue is a ground problem, right? The pump needs to be ground by the ECU correct (its the LB/O wire that I am jumping and that goes to the ECU). Sothe problem is either the ECU or the wire from the ECU to the OBD ( or that junction before that). I am I right?
 

ecgreen

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So this is what the LB/O wires look like on the back of the connector to the relay. looks like a bad connection to me - you can see the exposed wire that is not fully seated in the connector. I believe that goes to pin 22 on the ecu How would I test this? Or should I just fix it

badwire.jpg
 

farmer

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To test it, set the multimeter to ohm, and touch the exposed wire with one lead, and the connector with the other.

To fix that, you might be able to pull the pin out from the connector and carefully pry the tabs open, reseat it, and reinstall, but I've never tried. Otherwise I'd get a box of good heat shrink butt connectors, snip the intact wire 3-4" away from the connector, and connect them all together. Like (two wires)>[butt connector]-(single wire to relay)

Have you triple checked all your chassis grounds? for grins try running a temp ground wire from the ECM to the battery, that would prove/disprove a chassis ground issue.

If there's continuity at the relay plug, and an extra ground doesn't fix it, I'd say its the ECM
 

farmer

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According to car-part, theres a computer in Pelham, and one in New Ipswich, price listed only for the one in new Ipswich, $45
 

ecgreen

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To test it, set the multimeter to ohm, and touch the exposed wire with one lead, and the connector with the other.

To fix that, you might be able to pull the pin out from the connector and carefully pry the tabs open, reseat it, and reinstall, but I've never tried. Otherwise I'd get a box of good heat shrink butt connectors, snip the intact wire 3-4" away from the connector, and connect them all together. Like (two wires)>[butt connector]-(single wire to relay)

Have you triple checked all your chassis grounds? for grins try running a temp ground wire from the ECM to the battery, that would prove/disprove a chassis ground issue.

If there's continuity at the relay plug, and an extra ground doesn't fix it, I'd say its the ECM
OK, I just pulled that connector pin out and I ran a voltmeter between the battery negative and that wire (both on the exposed wire and various parts of the connector pin. Got no resitance. That tells me the ground is good.

I'll try the extra ground thing, but all signs point to ECM I think.

This diagnostic thing is kinda fun.
 

farmer

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farmer

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If you wind up junkyarding for a ECM, want to keep an eye out for a gauge cluster without a tach? I have a 2nd gen dash like your Bronco, my tach doesn't do me any good with the v8
 

ecgreen

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If you wind up junkyarding for a ECM, want to keep an eye out for a gauge cluster without a tach? I have a 2nd gen dash like your Bronco, my tach doesn't do me any good with the v8
Will do!
 


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