Attention: TDR Forum Junkies The stock CKP sensor got erratic at 203k miles, the tachometer would falter and go to zero with loss of power, but it ran. One day it failed to start for 5 minutes, finally restarted on about 5th try; this spooked me to think the VP44 was going bad. The light came on, I read the codes, they indicated a faulty CKP, so I put a new one in and it fixed the problem.
The experience but got me to thinking I should change out the injector pump due to high service mileage (207k); I know, don't fix it if it's not broken! But it doesn't start on the 1st or 2nd compression stroke like it did when new, and MPG has drifted down from 19 to about 17. I did some figuring and found that the pump has run about 4000 hours and cycled about 1. 5 billion times assuming 50 mph average speed, so... . I decided to put in a new VP44 to keep on truckin for another 200k miles.
-->Question: is the woodruff key specific to the pump or the gear train? That is, should I install the new VP44 with the key that came with it, or used the key from the original unit?
Lift pump history: I've on my 2nd LP in the stock position, I added a booster LP (Carter HP unit same as stock, DP products) on the frame rail at 75k; fuel pressure at the filter ranges from 10 to 12; I also added a Watts 150A Water Hammer Arrestor (1/2") between the fuel filter and VP44 inlet to reduce the "water hammer" caused by the rotary vane pump at the inlet end of the VP44. This is a miniature accumulator, or hydraulic shock absorber, mounted on a 1/2" bronze T with 3/8" hose barbs for the hose connections.
I noticed, as others have, that a conventional pressure gauge on the fuel filter gets hammered and quickly fatigues the bourdon tube then it cracks and leaks, or the isolator diaphragm fails, so you have to use a snubber or needle valve to dampen the hammering, or a glycerine filled gauge. To feel these shocks just reach down and grip the short rubber hose while the truck is running at idle.
These pulses may only be a problem at idle when the VP44 vane pump is turning at 400 rpm (one-half engine rpm), which is 6. 66 revs/second, or 27 vane sweeps (suction pulses) per second (27 Hz) in the four vane pump. Apparently at higher RPM, cruising at 65 mph (1900 engine RPM) the VP44 vane pump pulsing is at 64 Hz and the hammering diminishes. I charge the Watts arrester at about 5 psi, and it absorbs most of the pulse energy.
My theory is that this "diesel hammer" effect is the root cause of the short LP life the stock setup suffers from. The hammering is transmitted upstream to the pressure regulator ball in the Carter LP, causing premature fatigue or failure of the pressure regulating spring, leading to a loss of output pressure in these pumps in our Dodge trucks. In a gas-carberateur application the flow would be smooth so the LP would run longer. (The new fix of putting the LP in the tank separates the LP from the VP by 10+ feet with more rubber hose elements, so the hammering may be reduced giving longer service life at this location. )
A low-tech alternative to the Watts unit would be to replace the short 6" hose segment between the 3/8" OD hard lines at the filter and VP44 inlet with a 24-inch fuel hose as a coild of 2 or 3 loops; this flexible element would absorb some energy and may give the LP a longer life. My original unit lasted 170k miles.
1999, Auto, 4x4, QC, Silver, Pyro, Boost, Fuel Pressure Gauges, silencer ring removed, pusher LP + stock LP, Watts shock arrestor on intake side of VP44, 207k miles and going strong.
The experience but got me to thinking I should change out the injector pump due to high service mileage (207k); I know, don't fix it if it's not broken! But it doesn't start on the 1st or 2nd compression stroke like it did when new, and MPG has drifted down from 19 to about 17. I did some figuring and found that the pump has run about 4000 hours and cycled about 1. 5 billion times assuming 50 mph average speed, so... . I decided to put in a new VP44 to keep on truckin for another 200k miles.
-->Question: is the woodruff key specific to the pump or the gear train? That is, should I install the new VP44 with the key that came with it, or used the key from the original unit?
Lift pump history: I've on my 2nd LP in the stock position, I added a booster LP (Carter HP unit same as stock, DP products) on the frame rail at 75k; fuel pressure at the filter ranges from 10 to 12; I also added a Watts 150A Water Hammer Arrestor (1/2") between the fuel filter and VP44 inlet to reduce the "water hammer" caused by the rotary vane pump at the inlet end of the VP44. This is a miniature accumulator, or hydraulic shock absorber, mounted on a 1/2" bronze T with 3/8" hose barbs for the hose connections.
I noticed, as others have, that a conventional pressure gauge on the fuel filter gets hammered and quickly fatigues the bourdon tube then it cracks and leaks, or the isolator diaphragm fails, so you have to use a snubber or needle valve to dampen the hammering, or a glycerine filled gauge. To feel these shocks just reach down and grip the short rubber hose while the truck is running at idle.
These pulses may only be a problem at idle when the VP44 vane pump is turning at 400 rpm (one-half engine rpm), which is 6. 66 revs/second, or 27 vane sweeps (suction pulses) per second (27 Hz) in the four vane pump. Apparently at higher RPM, cruising at 65 mph (1900 engine RPM) the VP44 vane pump pulsing is at 64 Hz and the hammering diminishes. I charge the Watts arrester at about 5 psi, and it absorbs most of the pulse energy.
My theory is that this "diesel hammer" effect is the root cause of the short LP life the stock setup suffers from. The hammering is transmitted upstream to the pressure regulator ball in the Carter LP, causing premature fatigue or failure of the pressure regulating spring, leading to a loss of output pressure in these pumps in our Dodge trucks. In a gas-carberateur application the flow would be smooth so the LP would run longer. (The new fix of putting the LP in the tank separates the LP from the VP by 10+ feet with more rubber hose elements, so the hammering may be reduced giving longer service life at this location. )
A low-tech alternative to the Watts unit would be to replace the short 6" hose segment between the 3/8" OD hard lines at the filter and VP44 inlet with a 24-inch fuel hose as a coild of 2 or 3 loops; this flexible element would absorb some energy and may give the LP a longer life. My original unit lasted 170k miles.
1999, Auto, 4x4, QC, Silver, Pyro, Boost, Fuel Pressure Gauges, silencer ring removed, pusher LP + stock LP, Watts shock arrestor on intake side of VP44, 207k miles and going strong.
