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Fuel pump wiring issue 5.3 LS Swap

J

jfkelley

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Guys need some guidance..I have an 1976 K10 4x4 with 5.3 /4L60e with stand alone harness ..I have power to everything except my fuel pump wire coming out of the harness ..I can get it running with the wire straight from the in tank fuel pump to the battery ..I ohmed the relays everything checked out ..Need to get it running right to get it to exhaust shop & Tuner ..Any suggestions? ..Thanks in advance..See pics below
https://ibb.co/zXH3xSF

https://ibb.co/Bnc2CxR

ibb.co

IMG-1101 hosted at ImgBB

Image IMG-1101 in the John Kelley's images album
ibb.co ibb.co
 
Make sure the relay is getting power and the power is going to your fuel pump, check fuses as well and trace the wiring. Even if it's connected verify the connection is solid.
 
Babaganoosh said:
Make sure the relay is getting power and the power is going to your fuel pump, check fuses as well and trace the wiring. Even if it's connected verify the connection is solid.
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Just checked and made sure that the relays are getting power with my test light , and everything lit up.. when I turn the engine over with the wire connected to the test like it doesn’t light up.. fixing to do it old school style. I’m just wire straight to the ignition key to work comes on.lol
 
You positive that wire has power going to it while cranking and in the run position?
 
Babaganoosh said:
You positive that wire has power going to it while cranking and in the run position?
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No, there’s no power in the yellow wire coming out of the harness..But when I check where the relay plugs in I have power and the Relays oHM out good .. I know I’m missing something I just don’t know what it’s probably from lack of sleep
 
Babaganoosh said:
Do you have a diagram of the harness used or what brand it is?
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No sir unfortunately I do not have instructions just labeled with those tags ..It was my old harness just reworked by a LS Shop but he’s not much on answering questions.. when I asked him what the yellow connects to his reply was “ Should be powered by the ignition relay when the key is in on/run”
 
jfkelley said:
... fixing to do it old school style. I’m just wire straight to the ignition key to work comes on.lol
Click to expand...
Don’t do that unless you’d like more wiring issues or a burnt truck. The wire coming off of the ignition may not be able to handle the current needed by the fuel pump and it may fry the wire. The smaller wire of the ignition goes to the relay which “turns on” a switch (the solenoid in the relay) to handle the higher current.
 
rampage said:
Don’t do that unless you’d like more wiring issues or a burnt truck. The wire coming off of the ignition may not be able to handle the current needed by the fuel pump and it may fry the wire. The smaller wire of the ignition goes to the relay which “turns on” a switch (the solenoid in the relay) to handle the higher current.
Click to expand...

When you say smaller wire are you talking about the yellow wire that says fuel pump on it?
 
The ecm is supposed to provide a ground to the fuel pump relay. If you provide a ground to the relay does it close ?
 
jfkelley said:
When you say smaller wire are you talking about the yellow wire that says fuel pump on it?
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Whatever wire you’re fixing to use that comes off of the ignition/going to the relay. Don’t run that directly to the fuel pump.
 
The relay should have 2 terminals with power when the key is on. 1 will be the control side, the side that the computer will provide the ground. The other will be the power source for the pump. the 4th terminal will be the line to the tank and pump. So if you were to remove the relay from the socket and jumper pump supply power to pump circuit out it should power the pump. this a temp test suggestion I do not recommend driving the truck with this jumper.
If the pump doesn't run when jumpered, time to trace the wiring and make sure you have terminals in proper cavities.

Use a test light on positive post of battery to check for ground.
 
Without a diagram it's a lot of guessing.

On OBD1 GM stuff, and I have no idea if LS is the same (would think yes) the ECM is what controls the relay. Key to "run" the pump should prime for a few seconds, then stop. When the engine is cranking and running, the relay should be closed, sending power to the pump. But again, the ECM is what controls that. It has to see a signal from the ignition system to know that the engine is rotating and needs fuel. Again, that's OBD1. Hopefully obd2 is the same.

Relay should have a large wire with constant 12V, and another of same size that runs to the pump. If the relay closes, those two wires are connected via the innards of the relay, and the pump should run. If the relay has 12V (constant, ie battery) to it, and the pump + wire is connected, but the pump never runs, either the relay is bad, miswired, or whatever tells the relay to close (ECM, pressure switch, ignition, who knows without a diagram) is not functioning properly.

*Wes beat me.
 
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dyeager535 said:
Without a diagram it's a lot of guessing.

On OBD1 GM stuff, and I have no idea if LS is the same (would think yes) the ECM is what controls the relay. Key to "run" the pump should prime for a few seconds, then stop. When the engine is cranking and running, the relay should be closed, sending power to the pump. But again, the ECM is what controls that. It has to see a signal from the ignition system to know that the engine is rotating and needs fuel. Again, that's OBD1. Hopefully obd2 is the same.

Relay should have a large wire with constant 12V, and another of same size that runs to the pump. If the relay closes, those two wires are connected via the innards of the relay, and the pump should run. If the relay has 12V to it, and the pump + wire is connected, but the pump never runs, either the relay is bad, miswired, or whatever tells the relay to close (ECM, pressure switch, ignition, who knows without a diagram) is not functioning properly.

*Wes best me.
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The LS is the same way
 
Well I found some info and it appears the ls ecm provides power, and not ground. Also there is a signal from the neutral safety switch the ecm is looking for.ls Fuel Pump Circuit.jpg
Not sure what this is exactly, is the only diagram I found with yellow wire in the fuel circuit.
 
rampage said:
Whatever wire you’re fixing to use that comes off of the ignition/going to the relay. Don’t run that directly to the fuel pump.
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Ok so that I understand this correctly find the ignition wire or come off the ignition plug in the fuse box take that wire to the yellow wire that says fuel pump that should activate the relay ...I'm sure I'm making this harder than it should be ...Where do you connect the wire that coming from the fuel pump?... Me and my son started this project and then he joined the Army and I'm trying to have it ready for him when he gets home from Basic and everyones help is truly appreciated
 
IDK can you see the diagram I posted ?

Please list the wire colors going to relay, and diameter/gauge if different
 
Wes Harden said:
Well I found some info and it appears the ls ecm provides power, and not ground. Also there is a signal from the neutral safety switch the ecm is looking for.View attachment 447838
Not sure what this is exactly, is the only diagram I found with yellow wire in the fuel circuit.
Click to expand...
That's a 2-speed fuel pump and the relay shown is just selecting the speed. The B/W wire is probably ground. Typically there's a 2nd relay that turns the pump on and off, which should be where the W/B wire at the bottom is going.
 
From the pictures, this is not a stock LS harness, so there's no reason to expect it to match any of the diagrams posted online. There should be some kind of instructions with the harness. Do you know what the intended application is for that relay box? Do you have a ground wire coming out of the relay box tied to chassis or something? If there's no ground for the relay coils, they won't close, even if power is routed correctly.

But yeah, if the yellow wire isn't changing states (either going hot/open or ground/open) as the key is turned, then it can't control the relay. Usually there are 2 fuses for the PCM and therefore multiple power connections, so if one of those circuits doesn't have power, a lot of the outputs won't work.
 
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