My stock lift pump failed and caused the VP44 to fail at 65K miles. My mechanic recommended and I had him install the Bosch in-tank lift pump MOPAR upgrade. Question: what is the idle fuel pressure specification? What would you expect fuel pressure to be on the road at moderate speed, level, unloaded? Full throttle fuel pressure spec?

 

This was just also replaced on mine by the dealership. The pump puts out 10psi at idle at the vp44. It holds at around 9-10 throughout acceleration and drops to about 8 when I open it wide up.

Interestingly the mech says its way more efficient than the motor mounted unit it replaced, which was having 10-12 at idle and dropping to around 6-8 at WOT, that just failed a couple months back reading 0 on the guage. He also said it flows higher volume which I can't wrap my head around since its running the same size lines to the IP and running the same pressure. But its working so far.

Kurt

 

You might check out our DDRP pump......I dont have much time right now, but do a search for it.....

 

I had my lift pump changed over to the intank style under warranty...

I was able to hold 10-12PSI at idle... Not bad Right?

At WOT i could pull my gauge down to just under 1PSI..

Not cool..

But I installed a Holley blue inline with the intank and Im getting 18PSI at idle, and cant Drop it below 11 PSI WOT with the box and smoke chip on..

 

Do what y'all want to, but if you lose a pump by the side of the road it is going to be a whale of a lot harder to get going again, not to mention you shouldnt run an in tank pump down past 1/4 tank remaining to keep the pump cool.

I switched my buddies 02 back to the engine mounted pump after he lost his in tank pump.

 

I asked the diesel mechanics at an Albuquerque dealership about the Bosch pump. Their response to a pressure spec was that there is NOT a pressure spec .... it is a flow spec. 45 fl oz of fuel in 25 seconds (the fuel pump 25 sec timer when you tic the starter). When asked .... given that flow spec, what is normally experienced for pressure at an idle? .... 7-10 psi (I get about 7 psi). Normal pressure at normal speeds and loads? ... about 5 psi (I get about 5-6 psi). When I step on it, I get about 3-4 psi. My Edge Monitor low fuel pressure alarm is set at 2 psi. On a further note, the mechanics said that they have had good overall experience with the Bosch lift pump and that it is standard equipment starting in 2005.

 

Funny thing is that fuel pressure is a measurement of restriction of flow. The more you restrict the flow of a pump, the higher pressure you will get. Now the ability to maintain pressure is excess flow, or putting more fuel to the pump than what is needed. If you dance on the fine line of engine requirements with pump flow, you will get big pressure drops under load. Assuming gauge is reading correctly and there is no other restrictions in the system.

 

Diesel-Dan,

This is puzzling to me also .... pump head curves and system head loss curves and the like. We discussed the old pressure minimum spec for the block mounted lift pump (10psi, I believe) trying to rationalize the change. But apparently according to Dodge (per the mechanics) for the mechanical system configuration, if the Bosch lift pump can move the required volume rate to a container teed to the system before the VP44, then the VP44 requirements are satisfied. What is the flow/pressure spec for 2005 or later? What is the best way to get to the horses mouth?

Thanks for the comeback!

 

No prob.....eh..i know somewhere we have flow specs on the stockers...maybe not an in-tank...but the engine mounted units....

Well if you have good flow and you know your constant (Fuel demand of the VP); you should be able to use a volume test to see if the pump is going to hold pressure. Prob is that you do the test free flow...so say if you had a regulator in the lift pump that was messing up due to debris or something else...it wouldn't show up in that test. The only way to find that one is pressure gauge. BUT you have a whole can of worms that can factor into that as well.

BUT say if you do them both....you should have a good set of results to prove what is good and bad.

I see SOOOOOO many gauges go bad and the pump get blamed. Whether it be a sending unit, isolator, gauge, ect……confirming a gauge is not the issue should be the first step. Especially with a stock pump. I bet there has been thousands of stock pumps replaced that didn’t need it due to gauge error.

 

i have installed hundreds of the in-tank pumps and have not seen 1 fail yet. i run both pumps and regulate them. if the engine pump fails fuel will still flow through.

 

rigsy340, I will send you a failed one.

Thankfully he was close to home when it went and he limped it in.

 

The bottom line with volume vs pressure is that a set pressure at a given load will tell you if you have volume all things being equal.

Meaning, if you have a pump that will flow 2cc more fuel than the VP44 can ever consume, it should still show as positive pressure as there is a surplus of fuel. Or resistance as mentioned.

The free flow spec was introduced due to the number of warrantied pumps IMO. Nearly any pump, including one that may only be able to make 5psi at idle due to a stuck bypass can pass the free flow test.

We have a number of these failed in tank pumps on the bench and that's why we developed the new Draw Straw to make replacement of these units easier. There's tons of them on the street and few of the stock pumps can keep up.

I know I have to change my dad's dealer installed in tank pump for a better solution.

Dave