Engine/Transmission (1998.5 - 2002) Yet another LP/VP thread...

[DaveN]

Alright - just replaced the VP44, and bought the factory in tank relocator kit, along with a pile of gages that are now on my A piller.



At idle, I'm getting 10psi at the VP. I'm due for a fuel filter change, so I haven't checked that yet. But at WOT, it drops to 5 or 4 psi. At WOT, 3100 RPM, I'm down to two psi at the VP44. This only lasts for a second or two, once it shifts then it goes back up to four or so.



I'm not worried about starving the pump, but I don't know about what the actual requirements are for the VP. I'm sure there's 47 different opinions on it, some guys will want to say you need 15 PSI all the time, others will say this is OK - does anyone have any type of spec from Bosch on this, or some data to back up the minimum fuel pressure spec?

 

[Timbeaux38]

I'm sure there's 47 different opinions on it, some guys will want to say you need 15 PSI all the time, others will say this is OK - does anyone have any type of spec from Bosch on this, or some data to back up the minimum fuel pressure spec?

I hate to be the one to break it to you, but you will probably find that there will be 47 opinions about bosch spec too. What it boils down to is what you are comfortable with. You read threads where guys never get below 15psi and have a failure, and I personally have seen 0. 0 on mine before my current setup, and it still rocks along. Me personally, I like the flow test as opposed to the psi test. I'm getting 18 lbs with 1/2 inch fuel lines, that is more volume than with stock lines at the same pressure, no doubt.

 

[Fishin Guide]

Alright - just replaced the VP44, and bought the factory in tank relocator kit, along with a pile of gages that are now on my A piller.



At idle, I'm getting 10psi at the VP. I'm due for a fuel filter change, so I haven't checked that yet. But at WOT, it drops to 5 or 4 psi. At WOT, 3100 RPM, I'm down to two psi at the VP44. This only lasts for a second or two, once it shifts then it goes back up to four or so.



I'm not worried about starving the pump, but I don't know about what the actual requirements are for the VP. I'm sure there's 47 different opinions on it, some guys will want to say you need 15 PSI all the time, others will say this is OK - does anyone have any type of spec from Bosch on this, or some data to back up the minimum fuel pressure spec?

You are correct. There are as many opinions as there are people.



Mine is to be sure that the pump is not able to consume more volume than is available. While a gauge often shows us that some pressure is present, there is no way to measure volume. I personally would like to see no less than 10 psi under any condition. This is to overcome any restrictions to the fuel to enter the inlet of the VP and to fully fill it's fuel volume.



You are probably getting good volume and any pressure above zero is technically ok. However, I have seen what happens to trucks that see 5 psi at WOT. And the pumps just do not seems to last. My dad got the new pump and he has eaten 2 VPs since then. His truck is stock except for a 4" exhaust, BHAF and gauges. No fueling mods, ever.



In this example, he tows a small 5er and routinely runs the pressure down to the single digits. The VPs have been replaced under warranty. When he nears the end of that, we are adding a F1 Helix 2 cam and a 12Valve lift pump. This is due to the success I have had with my and a few other trucks I have modded this way.



Dave

 

[Fishin Guide]

I'm getting 18 lbs with 1/2 inch fuel lines, that is more volume than with stock lines at the same pressure, no doubt.

Yes and no.



1/2" lines will flow more volume at the same pressure. However, the VP can only consume so much fuel. Also, you still have to shove that fuel through those tiny 12mm fittings. The line could even be bigger and you would get no help.



Afetr upgrading my fuel system, we found several points of restriction. They were the stock module and the plastic flex lines from the module to the fuel line and from the fuel line to the factory lift pump.



Bigger is better to a point. Then it's just for looks and to say it's better because it can flow more.



Pressure is pressure. And basically is the resitance to something. I am not saying that bigger lines don't help. But I feel the largest gains come from good fittings and better design.



Dave

 

[Moose Truck]

Dave, here is a PDF of what is going on in the tank with the "intank" DC lift pump



http://www.glacierdieselpower.com/images/PDFs/IntankPumpExposed.pdf



Pretty weird huh? Moose00

 

[Fishin Guide]

Dave, here is a PDF of what is going on in the tank with the "intank" DC lift pump



http://www.glacierdieselpower.com/images/PDFs/IntankPumpExposed.pdf



Pretty weird huh? Moose00

It's a pretty good read. I think that now someone has put the pump in the tank, we can see something become available in the aftermarket hopefully. After all, the pump is finally where it belongs!!



Just by changing out my fuel system to the Vulcan Draw Straw and my BIG DOG fuel line kit, I was able to raise my WOT pressures from 22 psi to 37 psi. Now, I am running a mechanical pump. But it clearly illustrates the restrictions from the front of the truck into the bottom of the tank.



To me, big lines are great on the suction side. On the pressure side, they are far less important.



Dave

 

[bigdogdodge]

Hi,

A while back I emailed Cummins on this very subject and received a reply. Here is their response, "If you can have a positive pressure at the filter out fitting during cranking and max power your system should be OK. Anytime you see no pressure or a vacuum on the pressure out fitting stop the engine and fix the problem. The problems could be loose fuel supply line/fittings, cracked or broken supply line, plugged filter, tank filter or failed lift pump(#3946151. " I don't know if this helps but I have to believe that they would know best. Hope this helps.

 

[DMcPherson]

I beleive the vp needs at least 5 psi to keep the little chamber full, like said though, if yo uflow more volume you can get away with less pressure, on a stock system, try and keep it above 5

 

[Fishin Guide]

I beleive the vp needs at least 5 psi to keep the little chamber full, like said though, if yo uflow more volume you can get away with less pressure, on a stock system, try and keep it above 5

One of the things I found was interesting in regards to this. I had 20 psi of pressure and no volume.



How can that be? I guess I was sucking air somewhere and the pump was copressing both the air and fuel.



So, pressure is good as a basic diagnostic tool. But in the end, it's volume that gets it done with a little pressure backing it up. I would like to see the volume test perormed against a pressure head. So, at say 5PSI we get X LPM. I think it would tell us more than free flow into a bucket.



Dave

 

[DMcPherson]

I just copied and pasted this from cummins QSOL, sorry the small med large are the pics that wont copy



Fuel Lift Pump

(005-045)

Table of Contents

Summary

Initial Check

Remove

Disassemble

Test

Install



Summary



Measure pressure drop. Max: 34 kPa [5 psi].

Turn keyswitch ON and check fuel lift pump operation.

If pump not working, check voltage and resistance at lift pump. See detail.

If not to specification, check for good power supply.

Disconnect the fuel line between the lift pump and the fuel filter.

Plug the outlet of the lift pump.

Check for leaks at the lift pump or fuel line fittings.

Inspect the lift pump and the fittings.

Disconnect battery. Negative cable first.

Clean fittings and components.

Remove fuel lift pump inlet and outlet fuel lines (Procedure 006-024).

Disconnect the fuel lift pump harness connector.

Remove the mounting nuts and pull the lift pump down and out of bracket.

Disconnect electric fuel lift pump power leads.

Remove three cover screws and cover.

If suspect plugging, clean pump.

Measure output pressure. Use pressure gauge.

Turn keyswitch on and start engine. Max during cranking: 41 kPa [69 psi]. Min during idle: 69 kPa [10 psi].

Measure output pressure on fuel filter head. Use pressure gauge.

If not to specification, check for plugged inlet screen on pump. Clean if plugged.

Measure fuel inlet restriction. Refer to Procedure 006-020.

Install lift pump cover.

Install pump in mounting bracket. Torque: 12 N•m [106 in-lb].

Make sure the inlet and outlet are orientated properly. See detail.

Connect the harness connector to fuel lift pump.







Initial Check

TOC

WARNING



Fuel is flammable. Keep all cigarettes, flames, pilot lights, arcing equipment, and switches out of the work area and areas sharing ventilation to reduce the possibility of severe personal injury or death when working on the fuel system.



WARNING



Do not vent the fuel system on a hot engine; this can cause fuel to spill onto a hot exhaust manifold, which can cause a fire.



CAUTION



Do not operate the fuel system with a suction restriction of more than 3 psi.



A malfunctioning electric fuel lift pump can cause low power or rough running from the engine. The fuel lift pump can be cleaned and repaired to a limited extent.







SMALL | MEDIUM | LARGE







The pressure drop will increase as the filter removes contamination from the fuel. Therefore, a worn fuel lift pump will have reduced capacity to force fuel through a dirty filter. This can cause low engine power.

Pressure Drop Across the Fuel Filter

kpa psi

34 MAX 5

NOTE: Frequent filter replacement to get full power from the engine can indicate a worn fuel lift pump.







SMALL | MEDIUM | LARGE







Check for fuel lift pump operation by turning the vehicle keyswitch to the ON position and listening or feeling for operation.

NOTE: The fuel lift pump will run for 2 to 3 seconds when the keyswitch is first turned on and then it will shut off. It will run while the engine is running. It will also run for 25 seconds after a failed start attempt with the key on. This can be used to aid in priming the low-pressure lines after a filter replacement.







SMALL | MEDIUM | LARGE







If the fuel lift pump is not working, check for voltage and resistance at the lift pump.



If the voltage does not meet the specifications, check for a good power supply.

System Voltage Resistance

12 VDC MIN 9 VDC 0. 1 ohm

12 VDC MAX 2. 0 ohms

24 VDC MIN 21 VDC 0. 1 ohm

24 VDC MAX 4. 0 ohms













SMALL | MEDIUM | LARGE







Disconnect the fuel line between the lift pump and the fuel filter.







SMALL | MEDIUM | LARGE







Plug the outlet of the lift pump.

NOTE: All fuel must be drained from all fuel lines, if observed.



Apply the vacuum test to the fuel system and check the vacuum gauge. The vacuum can not exceed 381 to 508 mm-Hg [15 to 20 in-Hg].



If the system holds a vacuum (if the reading on the gauge does not reduce, the vacuum should not drop more than 2. 54 mm-Hg [0. 1 in-Hg] in a minute), then there is no leak in the fuel system.

NOTE: The vacuum test is completed if the fuel system holds vacuum for at least 5 minutes.



If the system does not hold vacuum (the reading on the gauge does not hold and reduce to 0 mm-Hg [0 in-Hg], then there is a leak in the fuel system.







SMALL | MEDIUM | LARGE







If the system does not hold a vacuum, check for leaks at the lift pump or fuel line fittings.







SMALL | MEDIUM | LARGE







Inspect the lift pump and the fittings. Replace and install parts that are malfunctioning or damaged.







SMALL | MEDIUM | LARGE









Remove

TOC

WARNING



Batteries can emit explosive gases. To reduce the possibility of personal injury, always ventilate the compartment before servicing the batteries. To reduce the possibility of arcing, remove the negative (-) battery cable first and attach the negative (-) battery cable last.



Disconnect the battery, negative (-) cable first.

NOTE: Thoroughly clean fittings and components before removal. Make sure that the debris, water, steam, or cleaning solution does not reach inside the fuel system.



Remove the fuel lift pump inlet and outlet fuel lines. Refer to Procedure 006-024.











SMALL | MEDIUM | LARGE







Disconnect the fuel lift pump harness connector.







SMALL | MEDIUM | LARGE







Remove the three fuel lift pump mounting nuts, and pull the lift pump down and out of its mounting bracket.







SMALL | MEDIUM | LARGE









Disassemble

TOC

WARNING



Fuel is flammable. Keep all cigarettes, flames, pilot lights, arcing equipment, and switches out of the work area and areas sharing ventilation to avoid severe personal injury or death when working on the fuel system.



Disconnect the electric fuel lift pump power leads.







SMALL | MEDIUM | LARGE







Remove the three screws on the cover of the fuel lift pump.



Remove the cover.







SMALL | MEDIUM | LARGE







The fuel lift pump is an electrically driven vane-type pump. It contains a relief valve in the head of the pump to recirculate fuel; this prevents over-pressurization of the injection pump and protects it from damage.



The fuel lift pump also has a screen on the inlet to catch debris and protect the pump. It can be cleaned if suspected of being plugged. A plugged inlet screen can cause low power and/or white smoke.



SMALL | MEDIUM | LARGE









Test

TOC



The output of the fuel lift pump can be checked through the following test:



* Measure the output pressure using a pressure gauge at the fuel filter head tap.









SMALL | MEDIUM | LARGE







Pressure Gauge and Hose, Part Number 3375932



Turn the keyswitch on, and start the engine. Measure the output pressure of the fuel lift pump by using pressure gauge, Part Number 3375932, at the tap on the inlet side of the fuel filter head.



The minimum lift pump pressure allowed during engine cranking is 41 kPa [6 psi]. Once the engine has started and is idling, the minimum lift pump pressure is 69 kPa [10 psi].

Lift Pump Pressure

kpa psi

Cranking 41 MAX 6

Running 69 MIN 10

NOTE: At initial key on, the lift pump will run for 2 to 3 seconds and then stop. During cranking, the fuel lift pump will run at half-duty cycle (approximately 6 psi at the output). Once the engine is running, the lift pump will run continuously. If the engine will not start, the lift pump can be checked by cranking the engine for a split second and releasing the keyswitch to the ON position. The lift pump will then run for 25 seconds.











SMALL | MEDIUM | LARGE







If the minimum pressure is not within specifications, check for a plugged inlet screen on the fuel lift pump, to disassemble the lift pump.



Clean the inlet screen if it is plugged.











SMALL | MEDIUM | LARGE







Measure the fuel inlet restriction before the fuel lift pump.



Measurable restriction is another possible cause for low lift pump pressure. Refer to Procedure 006-020.











SMALL | MEDIUM | LARGE









Install

TOC



Install the fuel lift pump cover.







SMALL | MEDIUM | LARGE







Install the fuel lift pump into the mounting bracket.

Torque Value: 12  n. m [106  in-lb ]

NOTE: Make sure the inlet and outlet are orientated properly. The words IN and OUT are stamped on the top of the fuel lift pump. The line from the tank must go to the IN side, and the line to the filter head must go to the OUT side.











SMALL | MEDIUM | LARGE







Connect the harness connector to the fuel lift pump.

NOTE: If the original lift pump had a non-integral connector, then extension harness, Part Number 4025182, will be required.







SMALL | MEDIUM | LARGE







Last Modified: 10-Feb-2006



Copyright ©2006

Cummins Inc.

All rights reserved

 

[DaveN]

Well, as always - tons of excellent information!



I suspected that there would be varying opinions. After reviewing all of the information provided - I've determined that statistical variation is going to determine whether what I have is good enough or not. I've heard of guys running 15 PSI and losing pumps, and a guy ar work complained of no power for six months - yes six months driving back and forth to work, and he finally broke down and put a gage on his and was running zero.



I'm kind of thinking that depending on the day of the week, the time of shift, and the phase of the moon that the VP was built determines whether your VP is going to last forever or crap out.



Thanks again for all the great info guys!

 

[DMcPherson]

I think your right. dodge did the vp in my truck about a year ago. a cuople months ago I put a guage on it, good idle pressure, and throttle and it would go to 0. aparently it had been that way for a year or so. I guess well see what happens. I now have 27 psi.

 

[rweis]

When our TDR club went to South East Power, they said the Bosch psi specs on the test stand were 10 - 15 psi during the test for correct calibration.



If that is for the calibration, it would seem that it would be correct for normal operation.



Just a thought,



Bob Weis

 

[rteig]

In tank filter

I have heard/read about the intake filter several times... . how do I get to it to change it?

 

[rteig]

In Tank Filter

Make that the "in tank" filter..... it has been a long day... . fire season seems to have hit here in MT!

 

[DMcPherson]

you will have to pull the pickup assy out of the tank