Rail pressure / loss of prime

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dak dmax

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Sep 4, 2020
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Minnesota
www.duramaxdiesels.com
Ight guys im working on my very first dmax 03 lb7 my injector went out a while back so I figure i wanted to build the engine anyways so I got 100 over injectors ats dual cp3 pump and a 200 gph air dog lift pump. Got all of in inatalled drove the truck maybe an hour parked it came back to start it 2 days later and i have a primeing issues it will fire up idle for maybe 30 sec the sputter out and die I hope back in the engine bay prime the system 25 pumps is what it take to get it started and same thing it dies agian. I cant figure it out brand new fuel filter ive looked at all the lines there not leaking I dont understand i just dropped like 6 grand on this truck and im ready to burn it to the grand and take the insurence money hahaha
Any tips would help guys thanx!
 
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N2BRK

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Dec 31, 2009
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Why are you needing to pump the manaul primer on the filter head, when you have an electronic lift pump? It should self prime, no? Are you sure that the AD is working?
 
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Bdsankey

Bdsankey

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N2BRK said:
Why are you needing to pump the manaul primer on the filter head, when you have an electronic lift pump? It should self prime, no? Are you sure that the AD is working?
Click to expand...

^ This. If there isn't a lift pump on the truck you better darn well get one.
 
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dak dmax

New member
Sep 4, 2020
7
1
3
Minnesota
www.duramaxdiesels.com
N2BRK said:
Why are you needing to pump the manaul primer on the filter head, when you have an electronic lift pump? It should self prime, no? Are you sure that the AD is working?
Click to expand...

I can feel it humming when the truck is running but I have power hooked up to the alternator because 1 thats what the stupid manual said and if i hooked it up to the battery it wouldnt shut off
 
Bdsankey

Bdsankey

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Feb 1, 2018
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dak dmax said:
I can feel it humming when the truck is running but I have power hooked up to the alternator because 1 thats what the stupid manual said and if i hooked it up to the battery it wouldnt shut off
Click to expand...

The battery and the alternator output lug are the same point electrically other than the alternator lug has a fused link between them to account for a possible short. If you had your lift pump hooked to the battery and it wouldn't turn off then you hooked it up incorrectly or your relay somehow was stuck in the engaged/closed position. Your lift pump should have 3 electrical connections that are a constant 12v+ source, a ground, and a switched source to turn the relay on which will then turn the lift pump on.


Make sure your lift pump isn't air locked and actually moving fuel. I've seen it happen on more than one occasion where someone installs a lift pump it was never primed properly causing a no-start.
 
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N2BRK

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Dec 31, 2009
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move the rtelay trigger to the HVAC system fuse under the hood (comes on with ignition). Key on, crack the AD filter and make sure it's pissing. Tighten it up and let it run a little. If you heard a change in the motor when you burped the AD filter, it was not primed. See if she'll start.
 
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