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Posted by: ppetion Feb 24 2012, 10:14 PM

Fuel pump question on 74 djet. Does the brain operates the fuel pump ? I connected all grounds and the relay board, fuses and relays are good , the engine is not yet in the car, when I turn the key on, the fuel pump is not powered. Is it because the brain is not attached ? 

Posted by: Jon Fernandes Feb 24 2012, 10:38 PM

Did you check to see if there's power at the pump when the key is turned on?

Posted by: ppetion Feb 24 2012, 10:41 PM

QUOTE(Jon Fernandes @ Feb 24 2012, 11:38 PM)

Posted by: underthetire Feb 24 2012, 10:47 PM

The "brain" does turn the pump on. It switches the ground on the fuel pump relay. It times for 1 second with key on, then turns the pump on when the ecu sees the trigger points trigger. At least that's how I understand the circuit. My megasquirt is tied in the same way.

Posted by: 76-914 Feb 25 2012, 08:41 AM

Yep. I chased that cat on my 1st 914. IIRC, it was a ground leg that switched it. #19 sticks in my mind but don't hold me to it.

Posted by: Prospectfarms Feb 25 2012, 09:28 AM

Unless I was certain the pump is operational, if I had any concerns about my FP or its circuit I'd first try to energize the pump directly from a 12 volt source with sufficient current. Might save time later speculating about it.

Posted by: underthetire Feb 25 2012, 11:01 AM

All you need to do is ground III on the relay board. I can't upload pics from my iPad, but it's on the pelican site.