Dodge Cummins Diesel Forum banner
1 - 13 of 13 Posts

·
Tech Specialist
Joined
·
1,065 Posts
Discussion Starter · #1 · (Edited)
Of necessity, one of the single largest issues of importance for the 24 valve Cummins trucks, is the absolute need to carefully monitor fuel pressure as supplied to the VP-44 injection pump.

That pump has proved to be somewhat sensitive to fuel lubricity, pressure and flow. It is both cooled and lubricated by the flow of fuel thru it - a fact further complicated by the steady decline of diesel lubricity as steady efforts to reduce sulphur content has also adversely affected the lubrication characteristics of our fuel.

A fuel pressure gauge is an absolute MUST for a knowledgeable 24 valve owner concerned about the health of his expensive VP-44. Next in importance, are steps available to enhance the fuel supply to the VP-44 - and one of the best and most used methods, is installation of some form of aftermarket fuel pump - either a substitute pump felt to be better than the OEM fuel pump (lift pump) - or a supplemental (pusher) pump to reinforce and enhance the ability of the OEM pump to do it's job.

Aftermarket pumps such as the FASS, RASP, and the currently popular Walbro are being used, as well as one of several available Carter types that are nearly identical to the stock OEM lift pump also manufactured by Carter.

The focus of this thread, is the use of a Carter 4600 "Pusher pump" as I have installed on my own ‘02 truck. Here's a shot of mine in original form, installed as most feel works best, down on the frame rail as close to the fuel tank as possible:



Mine has gone thru several evolutions to further enhance reliability and operation - those will be covered later. The added pusher pump needs power to operate - and most users prefer to pick off a small amount of current from the existing LP power circuit to power a relay that in turn provides contacts to take voltage direct from the battery to power the added pusher, and not draw added excessive power from the computer controlled primary LP circuit - here's a shot of the common Radio Shack relay with 20 amp contacts that I use:



Some users trying to simply power the added pusher pump directly off an available keyed circuit, quickly discovered that if fuel PSI above about 7PSI is applied to the VP-44 before and during attempts to start the engine, it won't start - due to an over-pressure sensor in the VP-44 that prevents engine starting.

The OEM setup, and the computer controlled circuit that control power to the OEM LP actually only powers the LP for a split second at key-on to prime the VP-44, then shuts down to allow the engine to start - then, once the engine fires, again powers the LP for normal engine operation. That's why the added relay, controlled by the same lead that powers the OEM LP is used, to key the added pusher in tandem with the OEM LP.

NOW, as to some suggested additions to the pusher pump as seen up above. One potential disadvantage of the added pusher is, if it should fail or stop for any reason, it's possible for it to block fuel flow and starve both the OEM LP and the VP-44 - a potentially serious event!

For that reason, I have devised a homebrew flip-flop valve that functions purely off fuel flow and pressure at the pusher pump - it is closed by system fuel pressure in normal operation, but will open if the pusher fails, and permit fuel flow AROUND the pump if that happens - it looks like this disassembled:



And as assembled on the pusher, ready to mount back on the truck:



It has been tested, and functions perfectly with no need for operator intervention - I built my own, but places like Jegs offer them for about $24 or so.

End result with my setup, is about 23 PSI fuel pressure at idle, and about 16 PSI at cruise, either empty or RV towing:



Full load up steep grades usually show about 12 PSI - totally adequate for proper VP-44 operation.

To those who might be critical of the rather wide range of PSI, I might mention my use of a Frantz sub-micron fuel filter in my systen that adds about a 4 PSI drop in full-load pressure due to the added restriction of that filter - I can live with that, since I still have plenty of pressure for my needs - and greatly value the vastly superior purity of fuel supplied to my VP-44.

My pusher setup has been on my truck since new, and has performed flawlessly for about 4 years and 40K miles - there are other good aftermarket setups available as kits - but at just under $100 in total cost at time of original installation, I'm fully satisfied with mine.

(THERE Chad - satisfied?) LOL!
 
  • Like
Reactions: Marq92

·
Registered
Joined
·
2,283 Posts
A guy can learn a lot from this site. Thanks for that write up seems like u know ur stuff!
 

·
Registered
Joined
·
384 Posts
Gary, you seem way more knowledgeable than me on this subject. I will let you or someone else explain how flow also plays in to the equation. Hence the Vulcan and similar kits.
 

·
Banned
Joined
·
1,659 Posts
mrmajestic said:
Gary, you seem way more knowledgeable than me on this subject. I will let you or someone else explain how flow also plays in to the equation. Hence the Vulcan and similar kits.
This is fairly obvious but, more flow = cooler and happier VP-44. Is that what you are asking? Or am I missing the point of the question?
 

·
Registered
Joined
·
384 Posts
I think that increased flow may be as important as pressure. I run 22 lbs. at idle but can easily drop to 5 lb. at WOT with 38 lbs. of boost. Maybe I was just reminding myself to install a line kit.
 

·
Banned
Joined
·
1,659 Posts
I believe that the reason that DC went from testing fuel pressure to testing flow was so they could pass a huge number of failing lift pumps that would not pass the pressure test. As far as Im concerned, DC did this to save big $ - not to help their customers.
 
G

·
Dr. Evil said:
I believe that the reason that DC went from testing fuel pressure to testing flow was so they could pass a huge number of failing lift pumps that would not pass the pressure test. As far as Im concerned, DC did this to save big $ - not to help their customers.

I agree...........I had one OEM l/p that would produce 12 psi at idle and at a slite I mean slite touch of the throttle and the psi went to zero........this pump prolly would have passed their flow test but not mine.......not for a second

OEM l/p flat scare the hell outa me
 

·
Tech Specialist
Joined
·
1,065 Posts
Discussion Starter · #10 ·
*IF* I could maintain a steady 5 PSI right at the VP-44 inlet under ALL engine operating conditions, I'd be happy as a clam! :thumbsup

As long as adequate fuel flow is available right at the VP-44, even at single digit PSI, that's really all that's necessary - the job of the DC supplied LP is only to SUPPLY FUEL to the VP-44, NOT to in any way pressurize the VP - that's the job of the larger and better engineered VP-44 internal vane pump that feeds and pressurizes the individual fuel injection plungers.

It has been pretty well demonstrated and proved that applying vast volumes and pressures of fuel to the VP-44 does NOTHING to improve it's performance, cool it or improve internal lubrication.

All external fuel supplied to the VP-44 IMMEDIATELY faces that internal vane pump, which has positive engagement spring-loaded vanes - we ain't gonna force ANYTHING past that pump - and it rotates in time with the rest of the internals of the VP-44, so only just so much fuel is going to circulate thru the VP, regardless of HOW much you might spend on efforts to crowd more thru it. In fact, excessive pressures might even damage some of the more sensitive seals and control diaphrams...

All the above comments come directly from the Bosch injection pump manual as used by Bosch certified pump rebuilders...
 

·
Diesel Junkie
Joined
·
4,604 Posts
Whitmore said:
OEM l/p flat scare the hell outa me

Thats why the 7psi max on my 3rd gen concerned me when I put my gauges on. Running stock , it never drops below 5psi.With the performance setting on the BD pup , it will drop to 4psi when I tromp on it.

Any 3rd gen guys that had simmilar fuel psi reading with the stock lp and have upgraded to an aftermarket , Id love to know what kind of readings your getting.
 

·
Tech Specialist
Joined
·
1,065 Posts
Discussion Starter · #13 · (Edited)
Gary, where do you get that flip-flop valve part # at jegs
Mine was homebrew, not from any commercial source. Since mine was made, there IS a commercial source for one at a cost of about $20 as I recall - I'll see if I can dig it up...

EDIT - EDIT!

The commercial bypass number as supplied in another thread is no longer available - if someone locates a reasonably priced one, please post it here - all the ones I find currently available run about $175 or more - one reason I originally built my own...;)
 
1 - 13 of 13 Posts
Top