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  #11  
Old 07-16-2019, 07:04 PM
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Originally Posted by Dr Dean View Post
Just because you have battery voltage with an open circuit doesn't mean you have it when connected. Each resistance in the circuit takes part of the voltage, or the correct term is a voltage drop. I have seen wires worn down to 1 strand out of an 18 gauge wire that will show battery voltage on an open circuit, but as soon as you connect the load the voltage goes to zero. In this case an ohm meter will lie to you, 1 strand of the wire will carry the tiny amount of current that the ohm meter uses.

Be wary of the open circuit voltage, same scenario as the ohm meter, almost no current will read okay on your voltmeter. I try to use voltage drops for my testing.

In your case on initial testing I would use back probe pins and check for battery voltage across the pump. That tells me I have a complete circuit and if I see less than battery voltage I know I have a resistance somewhere else. next is to test positive side to ground, should be battery voltage if not I know I have to chase it to the source.

Don't forget the ground side of the circuit. Once again looking at voltage drops, with the load connected back probe the ground side of the pump and run the other lead to a good ground. Voltage read here indicates a resistance in the ground circuit.
All good stuff posted here Dr. Thanks for taking the time to post it here.

I pulled the connector on the fuel pump and metered it while it was all under the truck and showed open. cut my hole in the bed to get to the fuel pump and while I had everything out in the open I checked again. HMMMM 11 ohms from power to ground wire, that means I have continuity through the pump motor.

Jumpered from the battery to the pump on both pos and neg. pump runs fine. Got the truck started and all is well with jumpers, tail end lights are a bit confused, Lights on no taillights brake lights or turn signals. The front all works, blinkers blink fast like a bulb out. Put truck in reverse and all the lights in the back come on real dim.

I ran a ground from the negative battery to the ground pin on the flat trailer connector and all the lights work properly and the truck runs like it should.

So I was sure the fuel pump was bad based on the ohm reading with my head all under the truck and 98 degrees in the sun. I SURE FOULED THAT UP!!
I have not purchased any parts yet so I am not in the hole for a fuel pump I did not need.

I have lost a ground, possibly 2, there is a black/White wire in the connector for the fuel pump, and a black wire with ring term bolted to frame.

I found a couple broken ground straps going to the frame of the truck I need to replace. The black /white wire runs up the frame and up towards the brake master cylinder. On the wiring diagram I have it shows the black/white wire running to the maf sensor and a couple other sensors. along with a connection point with other black/white and black wires in the harness. This is all in the plastic split loom and where it breaks out is all black taped up.

The sun will be down enough here in a little bit to go dig around on this some more.

Thanks again for the participation and helping me out.

Scott
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  #12  
Old 07-16-2019, 11:24 PM
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I had a feeling that it wasn't a pump that's why I typed it all out. I can say from experience that it's really embarrassing to replace a $3000 controller only to find out that it was a ground, and I'm the factory trained professional. It's even worse to hang a new $5000 ecm on the engine only to notice that it has a chip on it after putting the ecm on. Guess what the freaking chip failed causing the no start. I'm going to stop now before I climb up on my soap box about putting a chip on the engine.

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  #13  
Old 07-17-2019, 09:13 AM
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I had a feeling that it wasn't a pump that's why I typed it all out. I can say from experience that it's really embarrassing to replace a $3000 controller only to find out that it was a ground, and I'm the factory trained professional. It's even worse to hang a new $5000 ecm on the engine only to notice that it has a chip on it after putting the ecm on. Guess what the freaking chip failed causing the no start. I'm going to stop now before I climb up on my soap box about putting a chip on the engine.

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  #14  
Old 07-23-2019, 07:32 PM
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Well how about a couple of things?

Got the ground figured out, I ran a ground from the battery terminal negative on the body of the truck and the lights on the rear and the fuel pump worked,,,, ( wait for it ),,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, The lights worked properly without a hitch.

The truck started a couple of times and just cranked a few times. Grabbed meter and checked voltage at fuel pump and had 12 volts, checked with connector connected to fuel pump. Lead probes small enough to back probe connector. I put a jumper in place of the relay to keep power on. Pulled connector and no continuity through pump motor. I thumped the top of the tank where all the line connectors come out of the fuel pump and had continuity. Plugged in pump and it ran. (GRRRRRRRRRRR) this was able to be replicated a couple of times. Ain't it nice to have more than one issue at a time.

New ground wire and fuel pump and truck has not missed a beat starting up in the drive.

Scott
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  #15  
Old 07-23-2019, 07:54 PM
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Quote:
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Well how about a couple of things?

.

New ground wire and fuel pump and truck has not missed a beat starting up in the drive.

Scott
Good! I hope.
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  #16  
Old 07-23-2019, 08:47 PM
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Me too.

Scott


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  #17  
Old 07-27-2019, 04:33 AM
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Don't know where you are with this, but just talked with a guy that is replacing his son in laws fuse box on a GM truck. Evidently gets water damage and is a known problem. So if all isn't still working, this might be something to look at.
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