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Ole girl has been sitting for a good while. waiting for glow plugs to warm up I didn't hear fuel pump run. The FASS 150 has been flawless on the 01 dually over the years. 12.95V from battery across 30 to 87 on the relay but only 8.5V across 85 to 86 with ignition on. Ive never been good at diagnostics, seemed logical. power and ground from original carter pump. That 2 pin connector leads into large factory harness that's run along the block should have 12V right?

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For one you dont have glow plugs. You have a pair of grid heaters at the base of the intake horn that heat incoming air.

 Two, if the fass is connected thru the factory harness and controlled by yhe ECM your pump will not be running with just the key on. You should only get a short prime of the pump, a second or less. Bump the starter, no engine start and it should run for 20 seconds or so. Unless your pump is wired to a key on hot it should not run constantly unless the engine is running. 

  This is all based on the stock configuration of the pump control wiring. Any mods could change that. Did you install the FASS?


It does sound like relay might be failing but thats a bit over my head. That might explain the voltage loss. There is always 12v power to the pump but it is negatively switched. If I am not mistaken you have test the voltage on the 2 pins and not just the hot to any ground. This gets a bit over my head at times but I am sure someone will be along to help clarify.

Edited by dripley
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Across 85/86 the voltage should vary.   During cranking it should be about 6v and running it should be 12v.  You don't want that to die....  that is the signal for the fuel pump from your ECM.     With the key on after 2 seconds or so, there should be no power there.....   only during cranking, engine running, or the 25 second time during a crank with no start.  










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Thanks for the input guys. Went to check voltage at dueche connectors at pump. both wires fell off in my hand from corrosion thnx to these pesky Minnesota winters. fixed that and walla! got fuel.

Never ends tho, went to fire her up and nothing not even a click. 

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