12 Valve 2nd Gen Dodge Cummins 94-98 Discussion of 12 Valve 5.9 Liter Dodge Cummins Diesels with P7100 Injection Pumps

Bad lift pump?

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Old 03-14-2012, 12:13 PM
ricet07's Avatar
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Default Bad lift pump?

When I first bought the truck I had to just touch the throttle while turning it over to get her to fire. I adjusted the idle to 750 and that helped but now (months later) it takes about three 5-10 second cranks before she fires. I don't have a fp gauge so I don't know what it is running for psi at idle and WOT. Just wondering if the hard start was because of that or when they bite the dust, they bite the dust.
 
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Old 03-14-2012, 12:30 PM
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I'd suggest checking the fuel pressure asap,whether you have to get a gauge or use a diagnostic tool, idk. Your injection pump isn't designed to pull fuel from the tank, will likely chew itself to death rather quickly if asked to do so. It might also be a good idea to upgrade to an Airdog or FASS lift pump/filter system if finances allow. Either way, you want to make sure you have a functioning lift pump.
 
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Old 03-14-2012, 07:26 PM
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Going to run the fuel psi gauge on it tonight. I have seen something like this before and it was a air leak, on a buddies truck. I would love to run a airdog I'm just hoping its something else causing the problem that is simple and not a wallet killer. Thanks

---AutoMerged DoublePost---

Thinking about getting a Airdog, I have that damn prime lok fuel filter relocator on my truck and im sick of it being in the way so I figure I can do away with that and the LP with the airdog and hopefully solve my problem too. How do they go about using the hose and the set up on the injection pump (banjo). Anyone have any pics and recommendations?
 

Last edited by ricet07; 03-14-2012 at 07:26 PM. Reason: Automerged Doublepost
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Old 03-14-2012, 09:24 PM
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your stock lift pump is a 90 gpm at 14psi pump this is what i use and wouldn't trade it for anything

HIGH PERFORMANCE ELECTRIC FUEL PUMP 130 GPH CHEVY FORD | eBay
 
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Old 03-14-2012, 11:00 PM
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Isnt the p pump supposed to have at least 22 psi supply? Not sure just wondering
 
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Old 03-15-2012, 10:27 AM
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Originally Posted by ricet07
Isnt the p pump supposed to have at least 22 psi supply? Not sure just wondering
the info I was able to find out was a stock one put out 14psi that is what I was told my the dodge service department

probably have 20k on my pump no problems

makes it nice when you change the fuel filter
 
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Old 03-15-2012, 11:17 AM
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I think I'm going to run a airdog 2 and see how it does.
 
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Old 03-15-2012, 10:35 PM
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A simple way to test for a bad lift pump is by replacing the fuel filter. The first time I replaced it I filled the filter but there is always a little air, I started the truck and brought the idle to about 1000 and it died once it got the air. I had a bad lift pump and it took running on ether for ahwile while cracking fuel lines until the pump primed. Some guys will tell you a p7100 won't run with a bad lift pump but it will. Even with a bad lift pump my truck would start on the first crank with slight throttle. I find long cranks is all about the p7100, maybe air. My buddy just put a BD 300hp pump on his truck and it now starts on the first crank with no throttle and idles at 750. Before it took about 3secs with no throttle. Mine won't start without throttle at all. Then again I never cranked it past 5 secs before I stop and give it slight throttle, habits My engine has 570K miles
 

Last edited by 12v15004x4; 03-15-2012 at 10:47 PM.
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Old 03-15-2012, 11:41 PM
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Dammm570k
 
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Old 03-16-2012, 09:20 PM
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Originally Posted by 12v15004x4
A simple way to test for a bad lift pump is by replacing the fuel filter. The first time I replaced it I filled the filter but there is always a little air, I started the truck and brought the idle to about 1000 and it died once it got the air. I had a bad lift pump and it took running on ether for ahwile while cracking fuel lines until the pump primed. Some guys will tell you a p7100 won't run with a bad lift pump but it will. Even with a bad lift pump my truck would start on the first crank with slight throttle. I find long cranks is all about the p7100, maybe air. My buddy just put a BD 300hp pump on his truck and it now starts on the first crank with no throttle and idles at 750. Before it took about 3secs with no throttle. Mine won't start without throttle at all. Then again I never cranked it past 5 secs before I stop and give it slight throttle, habits My engine has 570K miles
It starts with no throttle now but just takes a couple of cranks. I noticed that the 1 and 3 injectors are weeping aroung the retainer nut so im thinking that its just getting air in the lines. Hooked the fuel pressure gauge up and had good pressure so im ruling out a bad lp. Im going to pull the lines and torque the retainer nuts down and see if that helps. Kind of thinking about just throwing a new set of sticks in it but undecided on what to go with. Dont want to spend more than 500 on a set if I dont have to, any suggestions on what to run with the mods in my sig and stock hx35 and no fuel plate anymore. I have heard mixed opinions on the 370's and I know guys who had to run bigger dv's with them or it chattered like an old lady at idle.
 


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