Why Does VP-44 Fail So Much?
10-20-2004 | 01:39 PM
#2
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Joined: May 2004
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From: South Surrey, B.C. Canada
The VP44 is the INJECTION PUMP not the lift pump. The lift pump
is a cummins or carter lift pump.
VP44=$1500.00
Lift Pump=$150.00
I've unfortunately replaced my VP44 while my lift pump is actually still good. Bought the truck second hand with the VP44 bad already. Crappy learning curve but I still love my truck! Best guess here is after all my reading is the VP44 "seems" to go out
when
1.) The lift pump fails
2.) Trucks are "chipped" for more power.
The VP44 is actually a very good pump and used in BMW WITHOUT any sort of secondary pump at all.
is a cummins or carter lift pump.
VP44=$1500.00
Lift Pump=$150.00
I've unfortunately replaced my VP44 while my lift pump is actually still good. Bought the truck second hand with the VP44 bad already. Crappy learning curve but I still love my truck! Best guess here is after all my reading is the VP44 "seems" to go out
when
1.) The lift pump fails
2.) Trucks are "chipped" for more power.
The VP44 is actually a very good pump and used in BMW WITHOUT any sort of secondary pump at all.
10-20-2004 | 01:43 PM
#3
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Joined: Apr 2004
Posts: 8,234
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From: Texas/Oklahoma Border
Most VP44 (injector pump) failures are a reaction to an undetected failure of the Lift Pump...thus, the reason for FP gauge.
The only other reason for VP44 faliure that I can imagine would be very high HP constantly pulling fuel pressure below 5+/- psi thereby reducing bypass fuel (returned to the tank)...which cools & lubricates the injector pump.
Lift pumps fail, IMO, due to excessive cycling from higher HP demands for more fuel. I am in the minority, but I think the LP is an OK design...works very well for stock motors most of the time. With the proper support (Wildcat Max Fuel Flow System) it can and does work well up to about 425 HP.
RJ
The only other reason for VP44 faliure that I can imagine would be very high HP constantly pulling fuel pressure below 5+/- psi thereby reducing bypass fuel (returned to the tank)...which cools & lubricates the injector pump.
Lift pumps fail, IMO, due to excessive cycling from higher HP demands for more fuel. I am in the minority, but I think the LP is an OK design...works very well for stock motors most of the time. With the proper support (Wildcat Max Fuel Flow System) it can and does work well up to about 425 HP.
RJ
10-20-2004 | 02:01 PM
#4
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Joined: Jan 2003
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From: Kentucky
Hmm...I thought people always talked bad about the VP-44? Wow...that's news to me that the VP-44 isn't the lift pump!
From what I can tell, high-pressure pumps (VP-44 in this case) have poor suction capability and must be primed by the lift pump, correct?
Where is the VP-44 mounted at? Where is the lift-pump located at?
From what I can tell, high-pressure pumps (VP-44 in this case) have poor suction capability and must be primed by the lift pump, correct?
Where is the VP-44 mounted at? Where is the lift-pump located at?
10-20-2004 | 02:10 PM
#5
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From: Texas/Oklahoma Border
10-20-2004 | 02:22 PM
#7
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Posts: 2,242
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From: Celina, TX
There is not a pump in the tank. And the fact that the lift pump has to suck fuel from the tank, is part of the reason for it's early failure. The electric pump was meant to push fuel, not pull it.
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10-20-2004 | 05:25 PM
#8
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Joined: Nov 2001
Posts: 3,733
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From: Austria Europe
Well, IMO the suction is no problem at all for the lift pump. Any rotary vane pump can be used to pull fuel without a problem.
On the BMW the VP44 has no need for a lift pump, the integrated rotary vane pump is enough to pull all the fuel the BMW needs and then some to cool and lube.
The big difference between those engines is that the BMW uses less fuel per revolution than the Cummins. Therefore there is more fuel available for cooling and lubing the pump. The integrated vane pump will pump a certain amount of fuel per revolution, some of it is injected, the rest goes back through the return line. With the Cummins needing lots of fuel per revolution compared to the 2.5l BMW diesel the ratio is somewhat biased towards injecting instead of cooling. Hence the need for an electrical lift pump.
The main disadvantage of any rotary vane pump is that it will produce pressure spikes on both sides- on the outlet side that's no problem with the VP44's integrated pump because the rest of the IP is clocked correctly to have the fuel pulse fill the high pressure pump element quicker.
The inlet side actually poses a problem. The fuel is not flowing in but gushing in and then stopped rapidly. This cycle repeats with a high frequency. So when the VP44 is taking a mouthfull the LP has to deliver, when it stops pressure rises and the bypass of the LP will open. VP44 next mouthfull- pressure drop- bypass closes- etc-etc. So the bypass valve of the LP sometimes literally gets hammered through it's seat. These pulses do also put strain on the other parts of the LP like the motor and the vanes.
Personally I had good results by simply replacing the stock steel lines with rather soft rubber lines with an id of 10mm. These lines can expand and contract and therefore form a kind of dampener on the pulses.
The only time when a rotary vane pump hates to suck fuel is when it's dry. It does need the fuel to cool and lube itself. Since the diesel should not have any air in the system at any time the pump will just produce a pressure differential between inlet and outlet and have no problem whatsoever to pull the fuel up some inches. (Problems would start at more than 4.5 meters -14.7 feet)- an idustry average for marine apps is to keep the suction heighth of gear pumps and vane pumps below 2.5 m -roughly 8 feet and they are still self priming and can run continuous duty.
Just my 2c
AlpineRAM
On the BMW the VP44 has no need for a lift pump, the integrated rotary vane pump is enough to pull all the fuel the BMW needs and then some to cool and lube.
The big difference between those engines is that the BMW uses less fuel per revolution than the Cummins. Therefore there is more fuel available for cooling and lubing the pump. The integrated vane pump will pump a certain amount of fuel per revolution, some of it is injected, the rest goes back through the return line. With the Cummins needing lots of fuel per revolution compared to the 2.5l BMW diesel the ratio is somewhat biased towards injecting instead of cooling. Hence the need for an electrical lift pump.
The main disadvantage of any rotary vane pump is that it will produce pressure spikes on both sides- on the outlet side that's no problem with the VP44's integrated pump because the rest of the IP is clocked correctly to have the fuel pulse fill the high pressure pump element quicker.
The inlet side actually poses a problem. The fuel is not flowing in but gushing in and then stopped rapidly. This cycle repeats with a high frequency. So when the VP44 is taking a mouthfull the LP has to deliver, when it stops pressure rises and the bypass of the LP will open. VP44 next mouthfull- pressure drop- bypass closes- etc-etc. So the bypass valve of the LP sometimes literally gets hammered through it's seat. These pulses do also put strain on the other parts of the LP like the motor and the vanes.
Personally I had good results by simply replacing the stock steel lines with rather soft rubber lines with an id of 10mm. These lines can expand and contract and therefore form a kind of dampener on the pulses.
The only time when a rotary vane pump hates to suck fuel is when it's dry. It does need the fuel to cool and lube itself. Since the diesel should not have any air in the system at any time the pump will just produce a pressure differential between inlet and outlet and have no problem whatsoever to pull the fuel up some inches. (Problems would start at more than 4.5 meters -14.7 feet)- an idustry average for marine apps is to keep the suction heighth of gear pumps and vane pumps below 2.5 m -roughly 8 feet and they are still self priming and can run continuous duty.
Just my 2c
AlpineRAM
10-20-2004 | 07:05 PM
#9
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Joined: Mar 2003
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From: Central VT
Can someone tell me where you hook up a fuel pressure gauge on the stock system? Does this differ from where I hook it up with a FASS? I plan on getting gauges and also getting a FASS setup eventually. Just curious about the differences in setup if any.
10-20-2004 | 07:16 PM
#10
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Joined: Feb 2004
Posts: 176
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From: Columbus, Indiana
I was told the VP44 usually fails due to the metering plunjer sticking. Bosch realized they had a problem at about 110,000 miles. They decided to use a brass sleeve to fix the problem. Those usually stuck at about 30,000 mi. Bosch has now went back to the steel sleeve. Up to about a year ago your replacement would have been a brass style. They are mostly out of the system now. Lack of a lift pump only speeds the sticking process.
Fire away.......
Fire away.......
but i did keep 49 of it thanks
10-21-2004 | 06:42 PM
#12
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Joined: Apr 2003
Posts: 6,564
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From: Cummins Technical Center, IN
Originally posted by rjohnson
Most VP44 (injector pump) failures are a reaction to an undetected failure of the Lift Pump...thus, the reason for FP gauge.
The only other reason for VP44 faliure that I can imagine would be very high HP constantly pulling fuel pressure below 5+/- psi thereby reducing bypass fuel (returned to the tank)...which cools & lubricates the pump.
Lift pumps fail, IMO, due to excessive cycling from higher HP demands for more fuel. I am in the minority, but I think the LP is an OK design...works very well for stock motors most of the time. With the proper support (Wildcat Max Fuel Flow System) it can and does work well up to about 425 HP.
RJ
Most VP44 (injector pump) failures are a reaction to an undetected failure of the Lift Pump...thus, the reason for FP gauge.
The only other reason for VP44 faliure that I can imagine would be very high HP constantly pulling fuel pressure below 5+/- psi thereby reducing bypass fuel (returned to the tank)...which cools & lubricates the pump.
Lift pumps fail, IMO, due to excessive cycling from higher HP demands for more fuel. I am in the minority, but I think the LP is an OK design...works very well for stock motors most of the time. With the proper support (Wildcat Max Fuel Flow System) it can and does work well up to about 425 HP.
RJ
Justin
10-21-2004 | 11:24 PM
#14
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From: The "real" Northern CA
Originally posted by AggieJustin
There is not a pump in the tank. And the fact that the lift pump has to suck fuel from the tank, is part of the reason for it's early failure. The electric pump was meant to push fuel, not pull it.
There is not a pump in the tank. And the fact that the lift pump has to suck fuel from the tank, is part of the reason for it's early failure. The electric pump was meant to push fuel, not pull it.
10-22-2004 | 11:33 AM
#15
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From: Cummins Technical Center, IN
Katoom is correct. If you look closely at the stock fuel system, there is a very strong siphon effect that basically prevents the "sucking" condition.
Now, if there's small air leak that allows the system to lose the siphon, then the pump will have to "work" to get it going again.
The only time you'll lose the siphon under normal conditions is when the fuel level in the tank falls below that level of the LP. Even then, the "suck" factor is minimal.
Justin
Now, if there's small air leak that allows the system to lose the siphon, then the pump will have to "work" to get it going again.
The only time you'll lose the siphon under normal conditions is when the fuel level in the tank falls below that level of the LP. Even then, the "suck" factor is minimal.
Justin