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how much is too much fuel pressure??

5253 Views 27 Replies 14 Participants Last post by  Ditch Baby
i want to know how much is too much fuel pressure for my truck?? i know it shouldn't dip below 5 lbs but how much is too much??
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With electric pumps, you can get hard hot starts above 20psi.

I have been running over 40psi for years. The only pump I have seen lost due to high pressure was last year and that pump had 2 years, 50K miles. It was running at 75psi.

Dave
 

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i want to know how much is too much fuel pressure for my truck?? i know it shouldn't dip below 5 lbs but how much is too much??
5psi? I have always heard never below 10psi and no more than 20psi. :thumbsup:
 

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Discussion Starter · #9 ·
vp is brand new, airdog used to sit at 15 psi then i had some trouble with it and somehow it droped down to 10.5 psi at idle then i stretched the spring inside of it and it sits at 17-18 i never see 20 or higher
 

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Discussion Starter · #10 ·
ad was wired to the alt and when changing the oil i accidently sparked the power wire on the alt and it blew the 140 amp fuse in the fuse block thats why the ad was acting up
 

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I run 28psi and 20 @ WOT no hard starts at all just a mystery fuel leak causing my hard starts, parking downhill takes care of that.
 

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if it's staying at 5 psi cruzin then you will want to fix. 10 psi or above is what you want at cruzin speed. If it's dropping to 5 psi say 0 to 80 mph WOT then levels out at 10 psi or above cruzin you should be fine.
 

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I run 28psi and 20 @ WOT no hard starts at all just a mystery fuel leak causing my hard starts, parking downhill takes care of that.
Over 20psi and your headed for diaphragm damage in the VP44. Once its damaged you have to replace the pump as an assembly or so I hear. The mystery fuel leak you describe sounds like the check valve or the line running down the back of the block however.

The check valve on the return port of the VP44 should open at 15psi or so. You want an adequate return volume of fuel so you should maintain higher than 10psi under all conditions. Remember this has no affect on the power output of the engine because this excess fuel is being returned to the tank, its only there to lubricate and cool the injection pump. I like to see my fuel pressure around 17-18psi at idle and not drop below 15 at WOT. :thumbsup:
 

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this check valve... if it was to leak, how much pressure comes out of it?

i have a fuel leak somewhere when im riding the truck hard. It coats the material on the firewall then drips down all over the driveway at night.

I went through and tightened the lines around that area, the return line on the back of the head i got a good bit of movement, same with the #6 injector. Has done it with and without the airdog installed.
 

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With electric pumps, you can get hard hot starts above 20psi.

I have been running over 40psi for years. The only pump I have seen lost due to high pressure was last year and that pump had 2 years, 50K miles. It was running at 75psi.

Dave
Isn't that like 20psi too much?:confused013:
 

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this check valve... if it was to leak, how much pressure comes out of it?

i have a fuel leak somewhere when im riding the truck hard. It coats the material on the firewall then drips down all over the driveway at night.

I went through and tightened the lines around that area, the return line on the back of the head i got a good bit of movement, same with the #6 injector. Has done it with and without the airdog installed.
I think the solution to your problem is actually getting quite clear. Its not to say that the overflow valve is not sticking, but I am suspecting that you have a leak on the return line that runs down the back of the block rather than a leak at an injector or a bad check valve. Looking the the VP44 follow the return line to the back of the block. It should met a T-junction where one line is coming from the cylinder head, another from the return on the VP44 (the line you followed), and another leading back to the fuel tank. The line leading from the head returns fuel from the fuel drain manifold. Both of these lines return excess fuel to the vehicles fuel tank. The banjo bolt on the back of the cylinder head has sealing washers that can and do go bad causing a fuel leak. From your description I would say this is the culprit of both your leak and hard starts. :thumbsup:
 

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So I am constantly told by the internet engineers.

Dave
The VE pumps in the early Cummins (89-93) could certainly be damaged by high fuel pressure. Its generally regarded as not being a good idea for the VP44, although I am yet to find a confirmed case of injection pump failure due to high pressure. I have found multiple reports of high fuel pressure causing hard start conditions however, and this leads me to believe that something awry is going on inside the injection pump. Without knowing exactly how the mechanical systems employed in the VP44 work I am hesitant to say much more about high pressure effects on the injection pump.

This being said the FSM states the return check valve opens at approximately 14psi. I would suspect running a few more PSI than that would be beneficial (i.e. 15-17psi.) In theory this would keep a fresh supply of fuel circulating through the injection pump aiding in cooling it. However as mentioned this is a just a theory, so take it with a grain of salt.

This is just my outtakes on how and why and I certainly accept constructive criticism. :SMART:
 
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