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Hi all I'm new to the forum and this is my first cummins truck. 1999 3500 It's completely stock aside from the vp44 and my newly installed raptor FRRP 100gph lift pump. The vp44 isn't a hotrod as far as I know I believe it's a stock replacement, previous owner had it done. The truck runs fine at any speed, matter of fact it has more pulling power and better throttle response so I'm reluctant to say my VP is bad? My issue is it is very hard to start after installing my raptor. The morning previous to install,  it started perfectly fine, fired extremely fast, got home from work did the install and it's been hard to start ever since. I have to give it some throttle otherwise it won't fire. I ordered a new vp44 overflow valve, past that any ideas?

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Since it sounds like everything was running fine before you installed a new lift pump, I would thoroughly recheck your work - especially at the fuel connections.  The fuel system may be losing its prime or drawing in air which will cause hard starts.  Fuel lines or fittings can leak air in while engine is off and still show no signs of leaking fuel when engine is running.

 

You should at least attach a fuel pressure test gauge at the VP44 inlet port to ensure the lift pump is doing its job.  

 

Before cranking the engine - try one bump start, then let go of the ignition key.  The lift pump should run for about 20 seconds - then try starting the engine.  If it starts right up it is an indication that you have a fuel supply problem.

 

The overflow valve is very reliable.  Don't start throwing parts at the problem until you have done some diagnostics.

 

- John

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On 10/15/2020 at 8:13 PM, Tractorman said:

Since it sounds like everything was running fine before you installed a new lift pump, I would thoroughly recheck your work - especially at the fuel connections.  The fuel system may be losing its prime or drawing in air which will cause hard starts.  Fuel lines or fittings can leak air in while engine is off and still show no signs of leaking fuel when engine is running.

 

You should at least attach a fuel pressure test gauge at the VP44 inlet port to ensure the lift pump is doing its job.  

 

Before cranking the engine - try one bump start, then let go of the ignition key.  The lift pump should run for about 20 seconds - then try starting the engine.  If it starts right up it is an indication that you have a fuel supply problem.

 

The overflow valve is very reliable.  Don't start throwing parts at the problem until you have done some diagnostics.

 

- John

I've tried bumping it and letting the pump run its full cycle before starting it and i still had to hit the throttle to get it to fire. Losing my prime makes alot of sense though because it acts like it's missing the prime by needing me to give it throttle to fire, I'll check my fitting connections and make sure everything is tight. The valve will be here tomorrow I will install it if I can't find any of my connections being my problem. Truck has 370k on it and I'm unsure if the previous owner used a new one when the vp was replaced

 

I'm also installing an edge juice with attitude that has gauge hook ups will my fuel pressure psi be accurate for seeing what the lift pump is doing? Or do I need to hook up a gauge at the vp port

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30 minutes ago, Djordan94 said:

I'm also installing an edge juice with attitude that has gauge hook ups will my fuel pressure psi be accurate for seeing what the lift pump is doing? Or do I need to hook up a gauge at the vp port

 

When I troubleshoot a fuel system, I want to have the most reliable means of testing available.  For me, that is a mechanical gauge at the inlet port of the VP44.

 

- John

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5 minutes ago, Tractorman said:

 

When I troubleshoot a fuel system, I want to have the most reliable means of testing available.  For me, that is a mechanical gauge at the inlet port of the VP44.

 

- John

I will pick up a gauge then, seems more trustable than an electronic sensor. I appreciate the advice brotha 

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On 10/15/2020 at 9:11 PM, Tractorman said:

 

When I troubleshoot a fuel system, I want to have the most reliable means of testing available.  For me, that is a mechanical gauge at the inlet port of the VP44.

 

- John

I will pick up a gauge then, seems more trustable than an electronic sensor. I appreciate the advice brotha 

 

 

So I checked all my fittings out, got a gauge I'm getting 18psi at idle and WOT is 8-10 psi 

My issue was a loose battery cable 😂 facepalm... Anyways she running great got my edge juice installed today and man oh man am I happy with her 

15 minutes ago, Djordan94 said:

I will pick up a gauge then, seems more trustable than an electronic sensor. I appreciate the advice brotha 

 

 

So I checked all my fittings out, got a gauge I'm getting 18psi at idle and WOT is 8-10 psi 

My issue was a loose battery cable 😂 facepalm... Anyways she running great got my edge juice installed today and man oh man am I happy with her 

Also I'm going to be adjusting my lift pump pressure tomorrow. I've been reading it shouldn't drop that much, I still have the stock fuel line from my filter to the vp so I'm assuming that is causing my drop 

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1 hour ago, Djordan94 said:

My issue was a loose battery cable 😂 facepalm...

 

Glad to hear the problem was a simple one.

 

1 hour ago, Djordan94 said:

So I checked all my fittings out, got a gauge I'm getting 18psi at idle and WOT is 8-10 psi

 

You will probably hear some differences of opinions here, but I think you are fine with 8-10 psi at WOT.  Inside the VP44 injection pump is a vane pump that flows fuel to the internal workings of the VP44 and to the overflow valve.  As long as the lift pump is delivering more fuel than the internal vane pump is consuming, there will always be a positive pressure at the inlet of the VP44.  Since your lift pump is showing a positive pressure (8-10 psi) at wide open throttle, you should be in good shape.

 

- John

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On 10/17/2020 at 8:53 PM, Tractorman said:

 

Glad to hear the problem was a simple one.

 

 

You will probably hear some differences of opinions here, but I think you are fine with 8-10 psi at WOT.  Inside the VP44 injection pump is a vane pump that flows fuel to the internal workings of the VP44 and to the overflow valve.  As long as the lift pump is delivering more fuel than the internal vane pump is consuming, there will always be a positive pressure at the inlet of the VP44.  Since your lift pump is showing a positive pressure (8-10 psi) at wide open throttle, you should be in good shape.

 

- John

I think It is Possible John Might be right about the fuel pressure always being positive or always ahead of the vane pump in the VP44. However, we have not seen detrimental effects from pressures higher than that. I will say it...... Commonly accepted pressures are to be no lower that 14 and no higher than 19 p.s.i. 14 is where the overflow valve opens and returns cooling fuel back to the tank and 19 is needed for when hauling heavy going up grades, that's when 8-10 might translate into slow damage to the VP during times of extreme heat build up. At 19 you are insuring maximum cooling with an open overflow valve. Additionally, I have tested newer mechanical gauges and found them to be showing higher than actual pressures by as much as 4 p.s.i higher. I have only tested two brands and the Isspro was closest with only 1 p.s.i. over actual pressure. I've always been a believer in Isspro brand gauges.

 

Tractorman has been a great help to this site and do not wish to slight in anyway.... again I say he may be correct although I do know the overflow valve will open and return more fuel at the 14 level so the accepted higher pressures are a level of insurance for maximum cooling when needed most.

 

I always use two stroke oil added to the fuel

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Cranking I see bouncing 7 to 12 PSI.

 

Running I see 17 at idle and 15 at WOT

 

I'm nowhere near 20 PSI or plus pressures. I'm very close to the stock pressure with good supply volume and plumbing since I only drop maybe a total of 2 to 3 PSI depending on filters how clean they are. The cranking pressure is a 50% duty cycle the ECM controls and it shoulbe lower than 12 PSI for proper starting above 12 PSI it becomes hard starting being the timing piston is being pushed advanced with fuel pressure. Hence why you need 7 to 12 PSI for cranking.

 

Way too many worry about the 14 PSI MIN pressure but the truth is you don't need 20+ PSI either. You nee to look at the cranking pressure as the engine is trying to start and lower the pressure to 7 to 12 bouncing PSI.  422k miles never had a hard start hot ever...

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1 hour ago, Mopar1973Man said:

Cranking I see bouncing 7 to 12 PSI.

 

Running I see 17 at idle and 15 at WOT

 

I'm nowhere near 20 PSI or plus pressures. I'm very close to the stock pressure with good supply volume and plumbing since I only drop maybe a total of 2 to 3 PSI depending on filters how clean they are. The cranking pressure is a 50% duty cycle the ECM controls and it shoulbe lower than 12 PSI for proper starting above 12 PSI it becomes hard starting being the timing piston is being pushed advanced with fuel pressure. Hence why you need 7 to 12 PSI for cranking.

 

Way too many worry about the 14 PSI MIN pressure but the truth is you don't need 20+ PSI either. You nee to look at the cranking pressure as the engine is trying to start and lower the pressure to 7 to 12 bouncing PSI.  422k miles never had a hard start hot ever...

Hey Wacky :poke:......... with 1/2 inch lines all the way I've pulled mine down by 4 p.si. while hauling heavy up a steep grade.

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2 hours ago, JAG1 said:

I think It is Possible John Might be right about the fuel pressure always being positive or always ahead of the vane pump in the VP44.

 

2 hours ago, JAG1 said:

Tractorman has been a great help to this site and do not wish to slight in anyway....

 

@JAG1, I very much appreciate your approach for considering a different concept regarding the role of the lift pump in a VP44 system.  I always want to give out the right information to the readers, even if it may differ from the current view.  I am  currently pursuing a way to show how the lift pump and the VP44 internal vane pump work together.

 

Thank you,

- John

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Your very welcome Tractorman.:thumb1:

 

Dieselfuture, yes even with Biodiesel because them stickers aren't very removable so it may always say bio when sometimes they can't get it. I really don't know the truth about it so I like the insurance the VP will always be okay.

 

 

Mopar1973Man, Sorry I called you Wacky..... just between friends is all boss.

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On 10/19/2020 at 8:22 AM, JAG1 said:

Hey Wacky :poke:......... with 1/2 inch lines all the way I've pulled mine down by 4 p.si. while hauling heavy up a steep grade.

 

But you have a Raptor WITHOUT a return line so under load you can produce cavitation (foaming of the fuel). Since there is no return to route that away you end up seeing the foam drop your fuel pressure deeper. This is the difference between a Raptor and an AirDog both produced by the same company and the same pump head but the full AirDog will return the air and foam back to the tank. Keeping my pressure stable. I'm even running bigger injectors, bigger turbo, and Quadzilla Tuner and still better on the stability of pressure. Then you most likely return and pick up out of the sender right? All that returned fuel is now foaming up in the sender bucket and adding air to the supplied fuel to the pump. My engine return is in the sender, AirDog return is in the filler neck, and the draw straw is nearly a foot away from both returns way less foaming and much cooler fuel. 

 

Average fuel temp right now 100 to 120*F max with fall weather.

 

drawstraw-fitting.jpg.12e51ef6d7bb7a533c

 

return-fuel-line.jpg.3c9bfa46ee172c243a6

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:punish:Bla bla bla, so what! You always have the best set up. At least I'm half way there with my return going into the filler neck on both trucks. Helps cool the fuel with the fill neck always in the wind and dumps away from the draw straw.

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