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Fuel Pump Issues


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10 hours ago, SoCalManche said:

As far as how I've measured it, the ignition is OFF, I disconnect the two three-pin connectors, one coming from the truck cab, and the other being the fuel pump itself. Once the fuel pump is disconnected, I take the other connector and back-probe the middle pin, and ground out to the chassis. That's how I get 40 ohms.

 

Sounds like this ohms measurement is through the fuel gauge in the cluster (C139_B). Reading could be normal for measurement taken.

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Need to take some voltage measurements. Use the following connectors callout. D1 and D2 are located under the hood, right side of engine compartment. Should have yellow covers on them.

 

D1_D2.jpg.b3f4725d0ce74c23fb6976fa8b81006e.jpg

 

D1_5 Battery Voltage (B+) Hot at all times.
D1_2 Battery Voltage (B+) Hot with KEY in RUN or CRANK position.
D1_6 Battery Voltage (B+) Hot with KEY in RUN position (only 2-3 seconds). This ones tricky, because of time limited.
Hope you can do these voltage measurements by yourself.

 

Forgot to mention, use battery negative terminal as DVOM ground.
 

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17 minutes ago, Ωhm said:

Need to take some voltage measurements. Use the following connectors callout. D1 and D2 are located under the hood, right side of engine compartment. Should have yellow covers on them.

 

D1_D2.jpg.b3f4725d0ce74c23fb6976fa8b81006e.jpg

 

D1_5 Battery Voltage (B+) Hot at all times.
D1_2 Battery Voltage (B+) Hot with KEY in RUN or CRANK position.
D1_6 Battery Voltage (B+) Hot with KEY in RUN position (only 2-3 seconds). This ones tricky, because of time limited.
Hope you can do these voltage measurements by yourself.

 

Forgot to mention, use battery negative terminal as DVOM ground.
 

D1_5: 12.5 volts

D1_2: 10.6-10.7 volts

D1_6: 1.8 volts

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14 minutes ago, Ωhm said:

 

If you have a choice, start with 15A fuse.

That worked to engage fuel pump via 15A fused jumper wire. Too much fuel entered the intake, so waiting a few minutes before trying to start again. Will come back with reading.

 

What does this mean for now?

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Fused jumper wire is doing what the Fuel Pump Relay should do. Suspect Fuel Pump Relay. You said you've try a few different relay, but that jumper wire is doing the same thing. Hope engine starts.

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13 minutes ago, Ωhm said:

Fused jumper wire is doing what the Fuel Pump Relay should do. Suspect Fuel Pump Relay. You said you've try a few different relay, but that jumper wire is doing the same thing. Hope engine starts.

Would there be a reason as to why the original relay clicks repeatedly when a new relay won't? 

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1 hour ago, Ωhm said:

Relays can fail in many different ways. Clicking means the relay coil can't hold the switching contact down on the other terminal. Does engine start with a new fuel pump relay installed?

No.

 

With jumper wire connected, fuel pump constantly primes but no start.

 

With original relay connected, no priming but will start with fuel added to TBI.

 

Help...lol...

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OK, well clearly it's not moving any fuel. 

 

Has it occurred to anyone that you have a bad pump????

 

It maybe that the pump has gone to ground and therefore the relay stammers. 

 


Time for a pump.......and go through ALL your grounds and cables and fused links...........ect.........

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2 minutes ago, Jeep Driver said:

OK, well clearly it's not moving any fuel. 

 

Has it occurred to anyone that you have a bad pump????

 

It maybe that the pump has gone to ground and therefore the relay stammers. 

 


Time for a pump.......and go through ALL your grounds and cables and fused links...........ect.........

I got a new pump orginally, which by the way isn't properly spec'd out for these trucks. But regardless, I took the original pump out, tested it at the battery, and it immediately started. Whenever I connect the jumper wire in the fuel pump relay, it immediate comes on. And it is definitely pushing fuel, because one of my fuel line retainer clips broke, and the new ones you buy need o-rings. I didn't know that, and so as soon as the jumper wire engaged between 30 and 87, fuel started coming out of the fuel lines at the connectors underneath the intake.

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