fuel pressure too high

[I6FREAK]

what is the issue with setting fuel pressure to higher levels, 20 or 25 psi so under load it can flow more volume keeping pressure say around 19 psi at wot. also I'veheard that as long as it starts then it is ok....is that the limiting factor of the pressure going into vp44?

[CUMMINSDIESELPWR]

i have heard that too high of pressure will actually cause some diaphram (metallic) to burst rendering the vp to fail. I could be wrong so dont take this for fact yet. Too high of pressure does have a negative affect on the water bleed port on the stock filter assembly, my neighber that i installed a raptor 150 on his found this out. When after i installed it i adjusted the flow to 20psi max at idle, checked with manual fuel pressure gauge on test port then told him we need to readjust it in a few days as it will break in and flow more.Well he called me up saying he found fuel under his truck (iddy bitty puddle bout 3"diameter) and also his diff was washed with fuel. It led me to find that the pressure was hitting 30psi at the test port on pre-start up lift pump run, then 25psi engine running. This was actually forcing the valve of the water in fuel dump to open and push fuel out.After readjusting the pressure back to 20psi max idle he hasnt mentioned any issues since. Nothing else was wes from fuel and you could see that it was soaking around the water dump valve. I also tightened the valve as well.Too high of pressure could work past the banjo bolt sealing washers... ?

[I6FREAK]

i have heard that too high of pressure will actually cause some diaphram (metallic) to burst rendering the vp to fail. I could be wrong so dont take this for fact yet. Too high of pressure does have a negative affect on the water bleed port on the stock filter assembly, my neighber that i installed a raptor 150 on his found this out. When after i installed it i adjusted the flow to 20psi max at idle, checked with manual fuel pressure gauge on test port then told him we need to readjust it in a few days as it will break in and flow more. Well he called me up saying he found fuel under his truck (iddy bitty puddle bout 3"diameter) and also his diff was washed with fuel. It led me to find that the pressure was hitting 30psi at the test port on pre-start up lift pump run, then 25psi engine running. This was actually forcing the valve of the water in fuel dump to open and push fuel out. After readjusting the pressure back to 20psi max idle he hasnt mentioned any issues since. Nothing else was wes from fuel and you could see that it was soaking around the water dump valve. I also tightened the valve as well. Too high of pressure could work past the banjo bolt sealing washers... ?

i am doing a little experiment that is a little overkill but i like to learn about first hand the relationship between pressure, flow, and cooling with my 1/2 inch hose setup. i have machined my own adapters with vp44 and filter outlet thread pitch(12mm-1.5) to a .5" hose barb out of 316l stainless steel. there is a decrease in pressure just at the vane pump caused by a relief in restriction in internal routing. so i am working on a high grade stainless steel spring alternative for my raptor (airdog 100 without builtin filter/h2o sep ). i have got 3 different ultra precision stainless springs ....so i am charting spring rate to fuel pressure for the configuration i have for my fuel system. my goal is to achieve 20 psi at vp vane pump at idle. i will be posting my report in the minimum fuel pressure post but i need to test 1 more spring rate. the variability that people see in their return line rate is from the position of the ball valve at that particular time of testing, which is almost always at idle. my opinnion is that unless you have a 150gph pump , at almost half wot, yes you have much more fuel flow going to injectors which is helpful butmaybe half or less going to return line. my goal is to have fuel and consistant flow going to return line. i believe that in conjunction with the heat alleviation in flow going into injector pump output to injectors. if pump produces twice the rpm, we have more than twice the heat energy alleviation of that additional heat energy from above idle rpms is needed imho. now i will hopefully go forward i will follow through with my thermodynamic protocol. i would appreciate any experience i can get from anyone. i wont be using anything more than 25 psi on lift pump output. i wish that the vp inlet would allow same or decent flow without engine running.

[CUMMINSDIESELPWR]

could one drill into the injector return galley on the front of the head and tap it to fit a banjo so not only will the injector excess flow to the back of the head but the new banjo coming off the high pressure side from the lift pump will also perform additional cooling through the galley? just run a T fitting after the filter assembly to achieve this.thoughts?

[Mopar1973Man]

Actually the majority of the reutrn flow is the overflow valve which is pinned open after 14 PSI this why there really no reason get get carried away with fuel pressure. Because after 14 PSI your just flooding the return line with fuel pressure racing back to the fuel tank. Now remember your supply line is 1/2" and your return lines ar 6mm (roughly 1/4") so eventiual you get to a choke point where the return line start gaining pressure because of it tiny size. Since there isn't a big line return kit with oversized overflow valve its just not going to work quite right...

[I6FREAK]

Actually the majority of the reutrn flow is the overflow valve which is pinned open after 14 PSI this why there really no reason get get carried away with fuel pressure. Because after 14 PSI your just flooding the return line with fuel pressure racing back to the fuel tank. Now remember your supply line is 1/2" and your return lines ar 6mm (roughly 1/4") so eventiual you get to a choke point where the return line start gaining pressure because of it tiny size. Since there isn't a big line return kit with oversized overflow valve its just not going to work quite right...

that is great to know, will it cause damage on any internal vp parts to run 22 psi going into vp? during the split second that the acc circuit cuts out during cranking, my relay that powers my lift pump is off, so i know the pcm sends lower voltage to pump circuit during cranking, is this potentially going to damage vp...truck starts in less than 1 second of circuit shutting off then on.

[Mopar1973Man]

As for the 22 PSI it unknown...You have to remember the orignal design was setup for 14-16 PSI which was the stock carter lift pump.As for the lift pump shutting down it normal. It called PWM (Pulse Wide Modulation) where the ECM command a on time and a OFF time in rapid series. With VP44 with torn diaphragms more people rig up a relay to cut the fuel signal during cranking because the VP44 will be hypersensitive to fuel pressure. But this condition is caused from running too low of fuel pressure.

[KATOOM]

Actually the majority of the reutrn flow is the overflow valve which is pinned open after 14 PSI this why there really no reason get get carried away with fuel pressure. Because after 14 PSI your just flooding the return line with fuel pressure racing back to the fuel tank. Now remember your supply line is 1/2" and your return lines ar 6mm (roughly 1/4") so eventiual you get to a choke point where the return line start gaining pressure because of it tiny size. Since there isn't a big line return kit with oversized overflow valve its just not going to work quite right...

This is exactly correct. Yes, excess fuel running through the VP is what removes the heat but using the "if more is good then a lot is better" mentality by just cranking up the fuel pressure could potentially work against you. We know how the VP is cooled and we know at what psi the VP is cooled but we dont know at what psi could be causing the return line to run under pressure and if that happening will affect the return process or affect VP performance or reliability. More research with more people running well over 20 psi may yield more answers to this but at the moment, staying between 15-20 psi at all times seems to be best. In saying this, we have yet to hear of someone who ruined their VP from "to much" fuel pressure.

[CUMMINSDIESELPWR]

with the cost of them and the time to replace, i dont think anyone wants to volunteer to do this test lol:doh:

[Mopar1973Man]

There was a guy that converted over to 12V cam and 12V lift pump and had 35-38 PSI going to the VP44. Needless to say he got ran off another forum for it. So as for knowing if it work or not I say it was running but as for long term damage I'll never know...Still I will not suggest crossing the 20 PSI mark there is no need for it...

[I6FREAK]

my goal was to get 20 psi to vp input, nothing more , but in order to achieve that i would have to set my lift pump to 22 or 23 psi. going through plumbing and filter canisteris causing 2 psi drop with a new filter. i change my filter every 10k anyway. i dont believe in waiting for pressure restriction. i would rather not gamble my new vp with 25 or 30 psi, especially if it wont make a difference in reliability.

[Mopar1973Man]

But the pressure inside the VP44 is only going to be 14 PSI because everything else is return to the tank. So there is no since in even trying...Just as long as the fuel pressure is above 14 PSI your golden..

[CUMMINSDIESELPWR]

my pressure sensor is at the return line on the vp and im reading ~19 at idle WOT about ~14. Ive had no problem with this for over a couple years now.

[KATOOM]

But the pressure inside the VP44 is only going to be 14 PSI because everything else is return to the tank. So there is no since in even trying....Just as long as the fuel pressure is above 14 PSI your golden.

Obviously I agree with you but given the fact that the FSM lists the overflow valve setting as "approximately" 14 psi and goes on to say that it should flow at 14-16 psi, I figure 15 psi is safer than 14 psi. That being said, how accurate is everyone's fuel pressure gauge? Well for example, my electronic fuel pressure gauge used to read 19.5 psi at idle but after changing to my new mechanical fuel pressure gauge, I was now reading 17.5 psi at idle. So I compared with a fuel pressure test gauge to find that my mechanical was within 1/2 a psi of the tester which means that I can only figure I wasn't getting accurate fuel pressure readings from my electrical gauge. My fault for trusting it for all those years, which is why I plumbed in a test port this time around so I can always confirm my mechanical gauge. Now I know I'm really getting 19.5 psi at idle. Point being is, I would advise someone to either test their fuel pressure gauge or set their regulator so that they never get below 16 psi.....just to be sure. Not worth the risk.

[Mopar1973Man]

Leave it to Katoom to bring out the inaccuracy angle. I do agree with you about that that why I'm push up wards to 19 @ idle and 17 @ WOT (Warm fuel) so when cold mornings come I'm dropped down to 17 @ idle and 15 @ WOT (< +32*F). Like yesterday I made a run down to Ontario, OR as I was travel through New Meadows, ID the the cold temp you can watch the fuel pressure sick just little. But in any case my pressure fall is the same 1-2 PSI empty and 2-3 PSI loaded with the trailer. So now assuming there is a +/- 1 PSI of slop in the system (overflow valve or the gauge) I still rather happy with the setup because worse case would put me at a low of 14 and a high of 20 PSI. But The Good Lord only knows how accurate my setup really is. But going back to the OP post of reaching well above 20 PSI at idle to make 19 PSI at WOT I still think is un-needed. So if the dash gauge and a test gauge are close to right and you well above 14 PSI but below 20 PSI you going to be fine. Pulling a quote from Blue Chip...

Blue Chip proved that 5 PSI, under load, made all the horsepower the VP44 pump could make, even with stock fuel lines, fittings and supply pump.

So raising fuel pressure above 14 PSI isn't going to change HP/TQ at all but it will increase the cooling ability. But once again about if a little is good then a lot more is better doesn't always work. But here again if you going to improve cooling ability you would have to create a 1/2" or 3/8" return line kit to improve return flow to the tank. Because at any rate your going to be fighting the same old 6mm ID lines back to the tank which has a flow reduced flow rate than your 1/2" big line kits.

[KATOOM]

Leave it to Katoom to bring out the inaccuracy angle.

Thats right. Keeping it real.