I've got my 2001 2500 5-speed 4x4 down with a lift pump problem.

 

Currently the newly replaced (in-line style, original location on engine) pump is primed and working during starting and maintains over 15 psi (that's the my of my gage). If the truck has sat for a few minutes, it will turn on briefly when the ignition is turned on, and it responds to blipping the starter by turning on for 25 seconds. I can hear good fuel flow returning to the tank (which I just cleaned up when replacing the fuel sender). Once I got the fuel circuit bled of air, it started just fine, but as soon as the engine starts, the lift pump shuts off. The injection pump is apparently able to pull enough fuel to keep idling, but can't rev up much- obviously it's starving for fuel. Gage slowly drops to zero.

 

I've swapped relays around for the fuel system and the ASD, with no improvement. I replaced the earlier lift pump with a fresh one, though the earlier one wasn't very old. There are no codes showing.

 

My search of the forums suggests that the ECM might have a burnt out circuit that runs the lift pump while the engine is running as opposed to starting. If that's so, I don't know why it would be, and I'd like to positively diagnose it before embarking on that repair. I have had strange lift pump behavior, including drops in pressure that vary with load but also come and go intermittently. I did replace the lift pump that came with the truck from the previous owner after I had is pressure drop to zero at times, and at this moment I have just replaced the one I put in, because I thought it was causing the problem... not so, apparently, so I guess I have a working spare.

 

Can anyone point me to any discussions that address this, or provide any further troubleshooting guidance?

 

If my ECM is the problem, I'm more tempted to set up a new relay off some other signal source to turn the pump on, in hopes that I can retain the shut-down function that would trigger in case of a wreck. I'm guessing a new or repaired ecm isn't in my budget.

 

Thanks for any ideas.

 

1 hour ago, piñon&juniper said:

Truck running again.

I'm glad you got it ironed out.

Relocating my lift pump to the frame helped my fuel pressure a lot. I put a spin-on strainer ahead of it since I gutted (on accident) the strainer/sock in the tank.

 

Here's the link to an amateur photo of my install.

https://mopar1973man.com/topic/18093-donaldson-upstream-spin-on-screen/

Edited July 14, 20222 yr by LorenS
Add link

11 hours ago, LorenS said:

Relocating my lift pump to the frame

What pump setup did you use?

FASS DRP 100. Relocating the stock pump to the frame was probably sufficient as the pressure rose and was consistent, but I had already bought the FASS so eventually installed it just to see if it gave any noticeable improvement. It may have been better at maintaining a higher pressure in a high load situation.

Ok, if anyone is still paying attention...

 

I got it all back together, and it runs, but something ain't right.

 

Summary of current state of affairs:

 

Problem 1 (Solved): ECU control of fuel pump is bypassed using @IBMobile's ASD relay technique. Works great.

 

Problem 2 (soon to be solved): The ASD is controlling an Airtex style inline lift pump in the stock location, not Airtex brand. Seems to work, but only pumps about half the expected volume of fuel when tested. This pump is brand new (Standard Ignition STD FTP5 from O'Reilly). With all my recent experience with the unreliability of these pumps, I have ordered an AirDog FP 100 upgrade to mount on the frame rail. I't not here yet.

 

Problem 3 (sort of solved): In messing with the fuel tank basket to replace the fuel sender and resolve a blockage of some kind, I replaced the original damaged fuel screen and another original fuel screen with my own made up draw tube in which I included a check valve. That valve now seems unnecessary, but it made sense at the time. The blockage issue is fixed, but the check valve probably adds a little unnecessary restriction to the line.

 

Problem 4 (not yet addressed): I have a pretty janky looking fuel pressure sender and gauge setup, and I'm not too confident in its accuracy. There have been wild variations in its readings. It's range is 0-15 psi, and to be useful, it should be more like 0-30. Historically it mostly stayed pegged and only dropped a little under heavy load. More recently it's at 12 or so at idle, 5-9 on light load driving, and plummets under heavier loads down to 1 or 2. Observing this behavior for the first time is what started me off on my lift pump quest. Even since getting things kind of working again, the gauge has behaved in both ways (reading mostly pegged and now, consistently, the more alarming low pressure readings).

 

Putting in a more reputable pump system will eliminate one of my variables. Getting a reliable fuel pressure gauge will eliminate another.

 

My Question for now is: Is there any known possibility of an issue in an otherwise functional VP44 that would cause intermittent fluctuations in the return fuel volume and/or the pressure set point for that return? As I assembled things the most recent time, I observed the return flow, which was steady at idle but which increased dramatically with RPM. Perhaps that's normal with the VP44's internal vane pump?

 

I'll update again after the AirDog installation.

 

Thanks

I'll be releasing a install video soon.

1 hour ago, piñon&juniper said:

As I assembled things the most recent time, I observed the return flow, which was steady at idle but which increased dramatically with RPM. Perhaps that's normal with the VP44's internal vane pump?

This is correct.  @Tractorman I believe did a bunch of testing around this topic.

I just found the article on that valve, so I'll pursue all that good info.

 

1 hour ago, piñon&juniper said:

My Question for now is: Is there any known possibility of an issue in an otherwise functional VP44 that would cause intermittent fluctuations in the return fuel volume and/or the pressure set point for that return? As I assembled things the most recent time, I observed the return flow, which was steady at idle but which increased dramatically with RPM. Perhaps that's normal with the VP44's internal vane pump?

 

The VP44 fixed displacement internal vane pump is the only pump that controls flow through the VP44 and over the 14 psi overflow valve returning fuel to the fuel tank.  Because the vane pump is fixed displacement, it will always flow more fuel as engine rpms are increased, therefore more return fuel.  None of the vane pump's operation has anything to do with the lift pump.  The lift pump's only purpose is to supply more fuel to the VP44 inlet than the internal vane pump can use.  That is all.  Nothing else.  

 

Because the lift pump supplies more fuel than the internal vane pump can use and the internal vane pump is rpm dependent, there will always be a positive pressure at the VP44 fuel inlet.  The fuel pressure at the VP44 inlet will be the highest when the engine is at idle and the lowest when engine is at full rpm under full throttle.

 

I have logged similar miles on my truck (367,000) and over 270,000 miles on a replaced VP44.  My frame-mounted FASS 65 gph lift pump pressure is the highest at idle - 12 psi.  It is 6 psi at under near full power.  The 6 psi is of no concern.  It is a positive pressure at the VP44 inlet.  I operated a OEM relayed in-tank lift pump (modified under warranty by Dodge) for over 150,000 miles on the replaced VP44 - that lift pump produced 6 psi at idle and 3 psi under near full power.  Again, 3 psi is a positive pressure - no concerns.

 

I think you are on the right track with getting a reliable gauge setup and installing a frame-mounted lift pump.  The frame-mount pump will allow the lift pump to behave like a pusher pump instead of a puller.  Most of the time the fuel level in the tank will be at or higher than the lift pump inlet.  

 

Lift pump pressure should be steady at any pressure reading.  You mention you still have concerns with blockage.  I think it would be worth installing a temporary vacuum gauge at the lift pump inlet (on your frame-mounted lift pump) to measure the pressure drop.  If there is no blockage, I would expect to see a minimal vacuum reading (less than 5" hg) while driving the truck.

 

I just noticed that you are reading the 14 psi overflow article.  A good read, but in my opinion this valve is not your problem.  The operation of this valve is largely misunderstood.  It very rarely fails - if ever.

 

- John

 

 

Edited July 18, 20222 yr by Tractorman

4 hours ago, Tractorman said:

I think it would be worth installing a temporary vacuum gauge at the lift pump inlet

Thanks for the thoughtful reply. Can you recommend a good vacuum gauge setup, and for that matter, a reputable and not too costly fuel pressure gauge I could consider?

 

More soon-

Here is just one of many vacuum gauges that would be suitable.  Just make a temporary tee fitting to work for your test.  You don't necessarily have to drive the truck.  Just bring the engine rpm up to 2,000 and hold.  This will bring the tank return flow to about 28 gph via the internal vane pump.  Observe the vacuum gage reading.

 

As far as a permanent fuel pressure gauge setup, I have no recommendation.  I use a warning light mounted in the dash.  The warning light is triggered by a low fuel pressure switch under the hood.  I have never felt a need for a fuel pressure gauge inside the cab.  

 

I have also added a fuel line with a check valve that loops around the lift pump.  This means that fuel flow to the VP44 inlet will not be disrupted in the event of a lift pump failure.  The VP44 internal vane pump will continue to draw fuel from the tank and around the disabled lift pump.  There will be no disruption of engine performance or fuel return flow to the tank.  I have proven this with my own truck on a 28 mile roundtrip to town with the electrical supply disconnected to the lift pump.   During the trip I applied full throttle several times, set cruise control for a few miles, and stopped / started the engine several times.  No change in performance.  Of course, the low fuel pressure warning lamp stayed on the for the whole trip (no lift pump pressure), but there was no cause for concern.  

 

- John

 

 

 

 

As ever John great write up with facts

I use a mechanical lift pump and would NEVER go back to electric EVER

 

my fuel pressure is 7psi ish at idle and 22psi at anything over 2k which my truck never sees, I have tested fuel return to tank and at 7psi (mechanical gauge) it is a serious amount of fuel, my fuel temps are never high, I've just done 200mile today and highest was 105f

My fuel return goes back to the basket ....still.... I have a return made for the filler neck but haven't got around to it

 

I don't buy into the 15psi minimum deal, I buy into flow return not pressure as my truck proves

 

And my mechanical pump is a DTT which everyone slated as rubbish..... not so  and my lines right now are 3/8th just not got around to 1/2" and I don't see the need

 

I did change the return valve on my truck a while ago...... while chasing PSI  actually  made jack difference

What I am not saying is that 5psi WOT on a rubbish electric chinese pump is enough,  5psi and 10 GPM return is fine

 

I am saying check your own return as I have and I believe @Tractorman has 

 

And go mechanical lift pump and forget about all this PSI rubbish

 

I swallowed a huge shipping, duty and Vat bill to get mine into the UK..... best thing I did