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Discussion Starter · #1 ·
Just bought this truck in july. I had read up on these trucks well before the purchase, so fuel pressure gauge was in on day 2. Mechanical gauge on top of fuel filter housing. When i put this in the pressure pegged the 15 psi gauge. My cummins mechanic said that i just had a strong pump. Over time the pressure came down to 10-12 psi. Then I checked and its down to 2-4 psi running at idle. I bumped the starter and check the gauge was up holding 9-10 psi, but running again it is back down low. I feel like air leak because the pressure relief at shut down is faster. Havent found time for in cab gauges yet. Any suggestions on electronic gauges.
 

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seriously use search I've answered this same topic so many times
 

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No offense but this topic is well exhausted and if you do a simple search on lift pumps, VP44's, fuel pressures, gauges, etc., you'll find more recent info than you'll care to read.
By the way, your lift pump is going out and taking your injection pump with it.
 

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Discussion Starter · #4 ·
I really appreciate your time to even read this post considering the topic. I spent a good deal of time searching and reading. I would not have posted this, but i have not seen anyone say a bad pump still put out 9-10 psi when the engine isn't running. I didn't see that difference before between idle and just the pump running alone.
 

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Your interest in making sure your truck is working properly is a move in the right step. Lurking around these diesel forums will give you lots of insight just by reading others stories. Yes, there is TONS of info on your topic which should supply you with hours of reading but to answer your question, we have all determined that the stock LP must be able to sustain 15 psi at idle and 10 psi at WOT. If your LP wont do that then you need to look into a new one or of course a better one. Stock LP's cost around $200 and will continue to fail but an after market pump will cost about $400 and come with a warranty. Tough to beat. The VP44 cant take low fuel pressure and WILL fail if you insist on running a weak LP. The fuel supply system is the weakest point of these trucks and most try to increase HP before they worry about their fuel pumps only to worry about their $1500 VP44 later. Good fuel supply and gauges then power increases is the right order.
 

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It's probably the lift pump but, just for s and grins, I have to ask when was the last time you changed the fuel filter?

If the gauge port you used is on the downstream side (as it should be) a clogged/clogging filter can/will cause restricted flow, thus pressure drop.
 

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10 psi at idle means a heck of a lot less at wot.
 

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I really appreciate your time to even read this post considering the topic. I spent a good deal of time searching and reading. I would not have posted this, but i have not seen anyone say a bad pump still put out 9-10 psi when the engine isn't running. I didn't see that difference before between idle and just the pump running alone.
Your pump is capable of pressurizing fuel, but cannot produce the volume needed to maintain pressure while some of the fuel is being used.

Mopar1973Man has some good info on this topic. Lift Pump Diagnostics
 

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Discussion Starter · #9 ·
Just to let you guys know, a mechanical 15 psi gauge doesn't last long in a 17-20 psi environment. Last week i tapped on the gauge and the needle jumped all over the place. Today my gauges arrived, and a quick test showed everything is fine...except the guage. Not sure of the funny behavior from the gauge, but that is better that the other possibilities. Thanks for the advice anyhow.
 
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