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Testing fuel pump


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89 MJ, 6 cyl.

 

Truck was running but then had an issue where it would run then cut off after a few seconds. Then it wouldn't run at all. On the starter relay, the wires that have the ring terminals shifted and contacted the blade terminal for the fuel pump. Fuel pump is new (put on the the PO) and was running just fine the other day. There is gas in the tank and the engine will run with starter fluid in the intake.

 

Turn key, relay sound like it clicks but no hum from the fuel pump. Zero pressure and no fuel at the fuel rail.

 

There is ~6V at the ballast. The ballast reads at 1.2ohms and I jumped the two wires, bypassing the ballast, and still no dice.

 

There is voltage at the plug at the harness next to the pump itself, but I don't know what the readings should be.

 

1. What voltages should be at the connector at the FP?

2. Should I wire the pump directly to the battery as a test to see if it runs?

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89 MJ, 6 cyl.

 

There is ~6V at the ballast. The ballast reads at 1.2ohms and I jumped the two wires, bypassing the ballast, and still no dice.

 

There is voltage at the plug at the harness next to the pump itself, but I don't know what the readings should be.

 

1. What voltages should be at the connector at the FP?

2. Should I wire the pump directly to the battery as a test to see if it runs?

 

You should have at least 10V-11V at the resistor. And at the pump connector. Before you wire 12V directly to the pump measure (ohms) between the pump ground wire and a clean shiny ground on the frame. I think you will have resistance and you have a bad ground to the pump due to corrosion.

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So should the starter relay also output 10-11V at the fuel pump terminal?

The 'front' of the ballast (closer to radiator) should have 10-11V and the 'back' should have ~6V?

 

There's a yellow wire and orange wire and a black wire. The black is ground and the orange runs from the ballast? What about the yellow? Which wire should have the 10-11V on the FP harness?

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I don't have a wiring diagram for your model. There will be three wires at the pump connector, power, ground, and the output from the float sensor to your fuel gauge. Use your meter w. the - lead on a good chassis ground, and probe the three pins w. the + lead. One should have at least 11VDC, that's your power lead. Then shift your - lead to the the black wire on the connector. The voltage should remain the same. If not, you have a bad ground wire at the connector. Oh, and the key should be on IGN.

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