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So I washed my engine and right after I had no fuel pressure. I just tested everything and found that the aftermarket relay that I assume came with the fass 90 fuel pump, doesn't have power to on of the pins. There is power from the battery positive terminal, but no power from what looks like is coming from the factory harness. Is there a fuel pump fuse somewhere?? I tested all the fuses I can see, all ok.

When I jump the relay pins the fuel pump turns on, so I just need to find out where the factory wires that run to the relay get their power from... thanks!
 

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Not sure about the FASS but the AirDog's have a fuse on the power coming from the battery.
 

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Discussion Starter #3
well yeah, that is the part that I have power from. The relay needs power from another source as well. the key on part. that is what I need
 

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In a normal setup the ECM powers the lift pump directlly. The factory relay only provides power to the ECM. I suppose the add on relay is controlled by ECM. It will not have power except in some conditions. It may have power in bump start mode for adequate testing.
 

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Disconnect the ecm plug. Clean and dry it and hope the ecm isn't fried.

The stock lift pump got it's power from the ecm through those tiny 18 ga wires. imo this is part of the reason the dodge engineers set it up to fail and why the after market ddrp pumps aren't as reliable as the relayed after market pumps. High amp draw electric motors need big wire. At least 10-12 ga. depending on length. Most manufacturers relay the fuel pump. Not dodge. They wanted to save $5.

On your relay Pin 85 gets the low amp signal from the ecm. Pin 86 sends the signal back to the ecm to ground. Pin 30 is the fused power from source (batt/power dist box). Pin 87 is power out to pump. Pin 87a is not connected to anything so it is power off when pin 85 has no signal.

Relays occasionally go bad but that doesn't sound like your problem. Like Dozer said you will only get a 2 second signal from the ecm if you just turn the key to on. Bump the starter and you get 25 seconds.

Hopefully your problem is just a wet/bad connection at the ecm plug. Good luck.
 

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Discussion Starter #6
ok thanks! that is exactly what i was looking for! I would not have been able to catch the 2 sec on without this info;) it has sat for a couple days now, so I assume it is dry. but i will double check tonight. thanks
 

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Disconnect the ecm plug. Clean and dry it and hope the ecm isn't fried.

The stock lift pump got it's power from the ecm through those tiny 18 ga wires. imo this is part of the reason the dodge engineers set it up to fail and why the after market ddrp pumps aren't as reliable as the relayed after market pumps. High amp draw electric motors need big wire. At least 10-12 ga. depending on length. Most manufacturers relay the fuel pump. Not dodge. They wanted to save $5.On your relay Pin 85 gets the low amp signal from the ecm. Pin 86 sends the signal back to the ecm to ground. Pin 30 is the fused power from source (batt/power dist box). Pin 87 is power out to pump. Pin 87a is not connected to anything so it is power off when pin 85 has no signal.

Relays occasionally go bad but that doesn't sound like your problem. Like Dozer said you will only get a 2 second signal from the ecm if you just turn the key to on. Bump the starter and you get 25 seconds.

Hopefully your problem is just a wet/bad connection at the ecm plug. Good luck.
Yeah, I don't understand this concept either. I assume the engineers didn't design the pump to draw a large amount of curent from the start. From that alone one can conclude that the pump is crap from the begining.
 

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Yeah, I don't understand this concept either. I assume the engineers didn't design the pump to draw a large amount of curent from the start. From that alone one can conclude that the pump is crap from the begining.

I found one of the cheap brands that brags their pump only draws 3 amps. Like that is good. :hehe:eek:h no! Don't waste amperage! :buttkick: we only got 136. :party018:
 
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