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I have an AirDog II 165 GPH lift pump and a full set of ISSPRO gauges.
I have my smarty set for the mileage tune because I have not done any transmission upgrades yet.


Couple weeks ago, I was driving on the highway and noticed that my fuel pressure gauge dropped to 0.

Killed the key, shifted to neutral, and coasted to the shoulder.


Normally when I turn the key to run, I hear the lift pump run for a split second. I did not hear it.

Being on the side of I-66 with cars and trucks passing me at 70+MPH, I did not have the time or desire to troubleshoot. I hotwired the pump straight to the battery and called it a night.

When I put the relay back in, everything worked normally. I figured it was an isolated incident.


This past week, I had the same problem. I noticed the pump did not run when I turned the key.
It also would not run if I bumped the starter.

I thought maybe my relay had gone bad, so I took the Fuel Heater relay from the PDC and installed it. (I have removed my stock fuel filter housing with heater.)

This did not work.

It turns out that I am not getting power to trigger the relay. There is no voltage across pins 85 and 86 of the relay.

Looking to the Bible (Factory Service Manual) page 8W-30-34 at the fuel transfer pump, I'm seeing that the stock lift pump is powered directly off the Engine Control Module.


My AirDog is set up according to the instructions.
The stock harness has a pigtail that connects to the factory lift pump connector on the side of the block. This powers the coil of the relay.
There is one wire that goes to the battery and one that goes to ground. The remainder of the harness connects to the motor on the AirDog.
(There are two additional connectors for a low fuel pressure light. I do not have that option because I have the gauge.)

This is NOT an AirDog problem. A lot of people jump on AirDog for low quality. Mine is an older version and it has no problem maintaining 18-20 PSI idle and 14-16 HP with the pedal to the floor.

This is a Cummins ECM problem.

Is this a sign of a failed ECM?
Has anyone else had these problems?
Were you able to find a solution?


I've still gotta sort through the wiring harness. I looked and didn't see any visible damage. I'm going to start peeling off the tape and loom to check further.

I've also gotta check Ground point 107 at the engine block, near the old lift pump location. I don't really see how that could go bad though.
 

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I've seen a few posts from guys with faulty ECM's who just used a toggle switch to run the lp. If you ecm does turn out to be the issue then just do that and let it last as long as it will.
 

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I think I would suspect the relay 1st.
Do the bump the starter test wile testing for power at the EMC connection.
 

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I would assume bad ECM at this point. I would trigger the LP relay using a key-on source. I you have the key on a lot, maybe also wire a switch inline so you can shut it off if you'd like to have just the key on for an extended time. But at least if its wired to a keyed ignition source, you won't have to worry about throwing a switch to run the truck or forgetting to shut it off. Make sure your switched source is also hot during start. Some key-on sources shut off during starting.

That'll hold you over until your ECM totally craps out.


Sent from AutoGuide.com Free App
 

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