WHAT is a "Pusher Pump", and why use one?
http://www.cumminsforum.com/articles/articles/45/1/WHAT-is-a-quotPusher-Pumpquot-and-why-use-one/Page1.html
Gary K7
By Gary K7
Published on 04/3/2007
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.
WHAT is a "Pusher Pump", and why use one?
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.
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.