Safe fuel pressure

[Mopar1973Man]

Something else that pass though my mind... If you coasting down a long grade... Lets say like me a forestry roads for over 15 miles during this time the injection pump is not pumping any fuel to the injectors because your coasting. Then if your fuel pressure is below 14 PSI that means the only fuel movement is through that tiny hole. Like myself hauling down a forestry road got my exhaust brake set on and never touch the throttle for over 15 miles. But my engine is singing along at 2K to 2.5K RPM's... This means the VP44 is twisting along at the same speed as the cam and there is little to no fuel movement... Another example. Coming off of Whitebird grade south of Grangeville, ID there is a 7% grade that I travel down not needing a exhaust brake but its 7 miles long and the engine is coasting the whole time so once again there is no fuel pushed to the injectors. Heat? Cooling? Lubrication? How can any of this occur at 5 PSI of fuel pressure? :shrug:Remember there is only 2 exit points... Injectors or the return line...

[flman]

I am not going to debate Chip, he is an upstanding business man, he is a VP44 pioneer, and your not gonna make him change his pages, he told me so . A lot of other people that sell pumps, have even copied alot of his info and experience from his web site. So lets get back to fuel pressure. Today the temps were in the high 30s. I was getting 16PSI at idle and 13PSI WOT:thumb1:I just got the 1/2" hoses, and plan on putting them on tomorrow. I hope to see even higher numbers, and I wont be depending on that tiny hole for return

[Mopar1973Man]

Don't get me wrong either... I'm not asking Chip to change either... But the mass tend to take the 5 PSI comment to far... Like over on your other post even he comment on the 10-15 is a normal pressure...

Hello Bob, I feel your frustration daily. I don't understand why Bosch can't build better computers. I suspect the real issue is the lead free solder that the tree huggers have caused all of us to use these days. It seems to me that computers on VP44s fail early on if they are going to fail, so consider the glass as being half full in your case. You got the replacement under warranty! As for optimum fuel pressure, back then there was no lift pump available that could make 10 psi under load, so that is one of the reasons we decided to do our test. My opinion based on experience is that 10-15 psi is optimum at all tiimes. Yes we got the pumps. Have a great day, Chip Fisher End of quote. There you go, Chip does not endorse 5 PSI.

This makes me feel better... (Sorry to ruffle feather...) As for my fuel pressure mine is hanging at 17 @ idle still and 15 @ WOT... Today temp was 49-50*F outside...

[flman]

Something else that pass though my mind... If you coasting down a long grade... Lets say like me a forestry roads for over 15 miles during this time the injection pump is not pumping any fuel to the injectors because your coasting. Then if your fuel pressure is below 14 PSI that means the only fuel movement is through that tiny hole. Like myself hauling down a forestry road got my exhaust brake set on and never touch the throttle for over 15 miles. But my engine is singing along at 2K to 2.5K RPM's... This means the VP44 is twisting along at the same speed as the cam and there is little to no fuel movement... Another example. Coming off of Whitebird grade south of Grangeville, ID there is a 7% grade that I travel down not needing a exhaust brake but its 7 miles long and the engine is coasting the whole time so once again there is no fuel pushed to the injectors. Heat? Cooling? Lubrication? How can any of this occur at 5 PSI of fuel pressure? Remember there is only 2 exit points... Injectors or the return line...

Glad you brought that up, today I took big blue through a mountainous region of Haines Falls Rt. 23A http://en.wikipedia.org/wiki/Route_23A_%28New_York%29 It is steep and winding, any ways big blue pulled most of it in 5th gear, had to down shift to 4th for sharp turns. On my way back down the Mountain, my fuel gauge was reading 12 psi in 4th gear, 2500 RPM, foot off the accelerator. I was wondering, why does it seem to be using fuel when I am coasting? I put it in N, and it coasted at 15 PSI. So go figure, it uses fuel in coast??

[flman]

But the mass tend to take the 5 PSI comment to far...

I know, a grump in another forum pointed out the 5 PSI claim, and I pointed them to the page that Chip sells the DDRP on. I got no reply Disclaimer, "I wont mention other forums by name any more."

[Mopar1973Man]

I pulled my previous post because I felt bad but you made a quote before I got rid of it... :banghead: As for the grumps and the big sites they tend to run with Chip's 5 PSI comment and take it as gospel. I got admit I've used several tidbits of Chip information too. Like the diagnostic information is dead nuts for telling if a VP44 is heading south. Like myself I stopped in a local rebuilder shop in Lewiston Idaho (happens to be a advertiser) and he's also saying that typical fuel pressure should be about 10-15 PSI. When I mention a AieDog 150 you get the "oh nevermind" comment... Which makes me feel good... I think it comes down to the fact of Cooling/Fuel pressure, soldering issues, fuel lubricity, and good filtering. Yea Chip did find a bunch of this stuff out and made life but for all of us. I tend to prefer the slightly highier number like 15 as a minimum to hopefully keep the VP44 overflow valve open more. The for filter I tend to prefer the 2-3 micron fleetguard filters. As for lubricity well that without saying... (2 Cycle Oil)

Glad you brought that up, today I took big blue through a mountainous region of Haines Falls Rt. 23A http://en.wikipedia.org/wiki/Route_23A_%28New_York%29 It is steep and winding, any ways big blue pulled most of it in 5th gear, had to down shift to 4th for sharp turns. On my way back down the Mountain, my fuel gauge was reading 12 psi in 4th gear, 2500 RPM, foot off the accelerator. I was wondering, why does it seem to be using fuel when I am coasting? I put it in N, and it coasted at 15 PSI. So go figure, it uses fuel in coast??

As for that I see a slight drop but only 0.5 PSI. So if I'm idling at 17 PSI coasting at any speed I see 16.5 PSI... As for consumption there shouldn't be any into the cylinders (injected) because there there would be acceleration. Now the fuzzy part... If there is only 2 exit points 1 being the injectors and 2 is a overflow valve... So either the VP44 is pushing fuel out the overflow valve or bleeding past the injectors into the return rail...

[flman]

Now the fuzzy part... If there is only 2 exit points 1 being the injectors and 2 is a overflow valve... So either the VP44 is pushing fuel out the overflow valve or bleeding past the injectors into the return rail...

That makes more sense, because it is not accelerating down the mountain. I guess I wont worry about it, will see what a 1/2' supply line does for it?

[flman]

You know, I read several years ago in the Cummins engine supplement manual that came with my truck, "do not turn off the key under acceleration or coast, something will break or need resetting in the injection pump" I wonder if that is why the fuel pressure drops at coast, because I the "something" I forgot??

[Mopar1973Man]

But I would assume the reason for it is that if you turn off the key the lift pump is shut down and there is ZERO fuel pressure to take care of the VP44 that is still spining...

[flman]

I will have to look at the manual, I thought the VP44 was capable of pulling fuel any ways, mine always did, even with dead lift pumps

[Mopar1973Man]

That's true... Yes... It will pull fuel by itsself but it not suggested because of the lack of pressure to keep it lubed and cooled properly...

[flman]

Actually the OE lift pumps would not allow fuel to free flow past the impeller in the event of failure. The new OEM ones were updated to allow bypass of the lift pump, so the VP to take in fuel on its own, to prevent imminent failure. But yeah, 1 VP failure was enough for me to put in a gauge, and not depend on that feature.

[flman]

I will have to look at the manual, I thought the VP44 was capable of pulling fuel any ways, mine always did, even with dead lift pumps

OK, I found it, it was actually in the Freightliner Drivers manual, under Cummins Engine operation. "Never turn off the ignition switch while going down hill. With the engine still in gear, fuel pressure will build up against the shut down valve and may prevent it from opening when the ignition is turned back on." And that is all they wrote.

[flman]

Ok, now lets get back on topic, I ran the 1/2" fuel line today, and I was able to get an all time high in pressures, I filled up after wards, so the fuel in the ground was probably warm, but it was in the mid 30s outdoors. Any ways, my pressure at idle is now 17 1/2 psi and 13 psi WOT. Almost had an FML moment cause the aluminium saddle tank has 1/2" taps. Any ways when I put on the Fass with the 3/8" lines, the flare connector I was going to use, sucked, and it pulled the nut right of the connector. So I rigged up a connection using a 3/8" flare x 3/8" NIPT. I also used a 1/2 x 3/8 bushing, but it had no hex on it, of course the 3/8 fitting came out leaving the bushing behind, with less then 1/4" to grab on to with channel locks, it broke of course, so I was under there with chisel, would not budge, cut it internally with a hacksaw and drove the chisel into the slots and got it out:pray:Ok, now it is back to work, I have a business that needs my attention as well. Talk to you all later.

[dayne808]

i bought an airtex pump and the pressure at WOT is like 12 psi but it idles really high at like 20psi. not really liking the pressure drop, but i guess i'm in the safe zone. with normal driving conditions it stays up in the 15-17 psi zone. i plan on buying an airdog or fass later even though my truck is just a DD, i rarely tow anything (sadly yes) i also agree with you guys about the importance of good press. i'm sure if it gets below 10psi on occasion it might not hurt the vp44, but steady romps on the throttle with no fuel pressure monitoring can lead to disaster hahaha

[guesswho512]

its kinda funny. no one votes for less than 10 psi. the farmer i bought the truck from said he kept a fuel filter under the seat. when he was pulling, it would lose power. he would pull over and change it. it even had one under the seat when i bought it. then one day i lost power. since i already had a filter in the truck, i pulled over and changed it. when i was filling up the cann, i bumped the starter 3 times...and still only had 1/3rd of it full! thats when i knew something wasn't right. that is when i stumbled across one of mopar1973man's post about 10psi min. i thought, "DUH, i wonder how long its been like this". the strange thing is that OE lift pumps can be crap out of the box. the auto part guy said "they(the manufacture) can't test them...other wise they would have fuel in them when you get it."

[Mopar1973Man]

the auto part guy said "they(the manufacture) can't test them...other wise they would have fuel in them when you get it."

I never thought about that... But yeah its true they are always dry...

[flman]

Actually all my Lift pumps were tied up in a plastic bag with fuel residue in them. Here is the part number for the LPs I used to buy Cummins 4943048, I am going to take a good look at one and see if it has a name on it, such as Carter or Bosch.

[FlatTwin]

I work with things like this all the time and thats BS. They test (or should test) the pumps. You want a bit of fuel in them to keep the seals from going dry. I work with aviation stuff like this and they are always checked. As noted above they are then placed in plastic bags and it takes care of any residue left in the pump. Same with injector pumps that are pretty much the same thing we use on jet engines, they are checked then bagged and sent out to us.

[guesswho512]

i hope i quit playing that game. i can tell you from experience that my pump moves at least 1 gallon in ~30sec:woot:, but that's another story.