Engine/Transmission (1998.5 - 2002) Why the VP44 pump fails

[tractorface]

Flow rate is the key

I agree We measure PSI because it is easy to do. Actual flow rate is more important and is would be a better measure for us. Flow rate could be reliably measured for about $1000. 00 give or take. We do this on large gensets all the time.

Someone could also do the calcs to find out what PSI we need with a certain size line etc. to give us Gary's 45 GPH. That is a pretty low rate actually.

We could shrink the supply line to increase PSI but that would be counter productive.

We need a good steady flow of fuel to the VP. Anyone know what the scale of the flow rates are for this pump. Is it always 45GPH at every RPM or does it vary? This type of info could be useful to a person putting together a system. Including return fuell rates etc. All of this is readily available on the larger Cummins gensets but I have not seen it for a 5. 9L Even so Gensets are a bit of a different animal in that run a constant RPM.



This means properly sized lines and pumps or a gravity feed system which is not very practical. Bigger is not always better.

Thinking out loud again.

 

[Gary - K7GLD]

Here's a key quote from a pretty smart guy, outta the thread I pointed to above: (bold emphasis is mine)



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For the record,



This whole thing for me started when i read the post about prime loc causing lift pump and the vp44 pump failures.



I found the whole post very interesting, and somewhat confusing, and i must confess i cheated while doing some of my r&d. I hired an engineer to check out the system but wanted to verify his findings before commenting.



I'll be honest with you , i thought this could be a good business opportunity, selling a complete fuel system upgrade.



When the engineer gave me his findings, his findings suported prime loc that pressure has very little meaning without flow.



Obviously i have invested a great amount of money to date in this project, i however believed it would be a good investment at the time.



Much to my chagrin, our testing proved the engineer and prime loc's position.



Based on all our findings, the most effective method is to simply move the oem lift pump closer to the tank and clean up some of the fittings(banjo bolts).



Installing a bigger line to feed the existing oem pump or aftermarket high performance pump at its factory location is a waste of money.



There really was no politically correct way of saying this, i know a lot of people have invested a lot of money.



I am not an expert in fuel systems but i have to conclude as long as your pressure does not drop below 2 psi,you will be ok with the oem system as is.



Next upgrade from there in my opinion would be to move the oem pump closer to the tank.



Keep in mind those of you in cold weather climates, the engine compartment does provide a warm location for your fuel pump to protect the fuel pump from geling.



From there a slightly higher flowing fuel pump located closer to the fuel tank, and once again if cold weather is a factor , the engine compartment is a warmer climate area.



Let me know how you feel about our findings, i am a transmission technician and i am trying to learn about the fuel systems just as you are.



Bill Kondolay

Diesel Transmission Technology

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[Guest]

"In the Grand scheme of things it doesn't suck (unless yours failed) it's just SO SO. "





sounds good, mine failed so mine sucked!, I ran stanadyne and always had good fp, I guess it grenaded for reasons unknown.

 

[tractorface]

Yep Your sucked

I agree with you. If yours fails It Sucks When mine fails, They all suck I don't run any additives until it gets cold. I have not seen any real evidence that they make a difference, except maybe to make the user feel better, which is important.

 

[rweis]

Well, we all measure fp to a fault. Why not measure fuel flow? How hard is that to do? There has got to be some sort of commercially available fuel flow meter that can be used.



They measure fuel flow in aircraft. What do boats measure?



It just can't be that hard.



We spend fairly significant amounts of $$$ all kinds of schemes to keep fuel FLOWING to the VP, ok so lets figuer out how to measure it.



I agree psi is a simple measure, but it does not measure flow (no new news there)



A quick search in GOOGLE listed a couple of pages of "fuel flow meters"



Bob Weis



LoganHill02,



Would you be interested in taking the lp apart or sending it to me and I'll take it apart so we can gather more data as to WHY it grenaded? I would be happy to pay the shipping.



So far I have heard of:

1. Motor failure

2. Motor to pump connector failure

3. Pump vane failure

4. Check valve failure

5. Screen failure

6. Electrical connection failure



Sure would be interesting to know if there are other reasons we can add to the list.

 

[tractorface]

Flow Rates?

I used a PAXI process input meter which can be had for about $300. 00 and a Badger flow meter (about $800. 00) with a pulsed output on the last job I did, it measured down to the tenth and could have been Hundreth's had I needed it to be. This was a stationary application with a big flow. The Badger I used would have to be changed to a smaller unit Hopefully cheaper as well.



Anyway Flo-scan is the industry standard for measuring fuel flow for consumption purposes. The only difference hear is we just need to measure the supply side only (I think).



I like the Red Lion PAXI with a Badger better. It is easier to install and works very well. Need real good Flow numbers to properly size a meter. For instance The Badger Nutating Disc meter model M25 (littlt brother to what I used last time) Wants to see a minimum of 1 gallon per minute and a maximum of 25 GPM in order to maintain accuracy. We would want to choose a smaller meter for our application.



I actually kinda have the go ahead to purchase what I need to install on my truck for "research" anyway I just need solid min and max flow numbers for the supply and return (and time to "Git er done"). I know the aproximate temp. range etc. just don't have any real flow numbers.

I am also certain a less $$ alternative is available just not sure how accurate it would be. When measuring consumption accuracy is important but just measuring a one way flow rate than accuracy is not so important in my mind.



http://www.floscan.com/html/index.asp

 

[Gary - K7GLD]

Considering that a fair number of owners, right now TODAY, are driving around with failed or failing lift pumps. and fuel FLOW is being accomplished largely or entirely by the VP-44 internal LP - what knowledge of any REAL value would be provided by a fuel flow meter? Obviously, fuel IS flowing, or the engine would die - the owner, relying on such a guage would check that flow guage, and be reassured, "everything is just dandy, I have FLOW... " The fuel pressure guage, on the other hand, would tell him his LP is DEAD!



As imperfect as some might consider PSI guages, they STILL provide the needed info as to fuel system performance under varying conditions that fuel flow guages alone will NOT provide.



Isn't it some in THIS group, who have complained at DC's change in LP testing, because THEY switched to testing FLOW RATES, instead of the LP's ability to produce a given PSI?

 

[tractorface]

Your right we would need to know what the optimal flow rates were Both in and out. I presume that if your "under" flowing fuel in your out rate would be low which would tell you that you are starving the pump. We would want to adjust our system to flow "out" The correct amount whatever that is. I have been working on flow in order to track Fuel consumption just thought this would be a side benefit.



Let's say the VP Can handle 45 gph max and we see 25 gph under full throttle, I assume this would show up by measuring the return rate. I will guess that if you are "Under" supplied your return rate would drop as your load increased. It would be interesting to see how helpful it could be. PSI is definetly easier for the masses. It would be nice to see some test trucks with flow meters on them though.

 

[BillGotthelf]

Well testing on my truck has given me the following. FASS fuel pump located as per manufacturers recommendations, replumbed the tank to FASS to 5/8" and FASS to VP44 to 5/8" with an AN8 90 degree angle retapped and drilled out into VP44. Return line was the original 3/8 supply line. Other mods below. Steady 70 mph readings: supply PSI 16, return PSI 14, Fuel flow into VP44 56 gph, fuel flow out of vp44 51. 3 gph. Fuel temp at start 86. 2 and at completion of test 102. 4. Newly rebuilt vp44 lasted 3 days before power dropped off (at least 1/3). Putting in another one tomorrow.

 

[rweis]

Well, you must have about the most instrumented VP I have heard of.



What do you think went wrong?



Acording to what I remember all the pressures and flow certainly would certainly be in the neighborhood.



Are you going to get an autopsy on the VP?



What do you think about the point of the fuel solenoid being held open too long / internal machining tolerances of the VP?



Bob Weis

 

[BillGotthelf]

Well I don't want to tear apart the vp44 as the parts place that I got it from wants it back ($1195 for the rebuild) to exchange for another. For the first 3 days truck ran fantastic but yesterday truck would barely chirp tires on 2nd gear shift. We checked evvvvverything. Narrowed down to vp44. I don't know if its circuit board or mechanical but power is way off. It was easy to add test solonoids to fuel line as we have a couple of areas that have hose/pipe/hose. I just wanted to see how warm the fuel would get. The outside air temp during test was 95 degrees so I did not think the 102. 4 was excessive.

 

[Gary - K7GLD]

Since I've added the Frantz fuel filter, it is real easy to lift the hood after a drive and put my hand on the metal canister to check for fuel heat - I was surprised (after reading speculation at extremely elevated fuel temps after longer engine running time) to find the canister is warm, but hardly significanly so - certainly NO danger of burning my fingers. I have a AC thermometer, might try actually getting a reading to see what I find...



I suppose a long hard run on a nearly empty fuel tank would make a difference, but like many here, I usually top off the tank at 1/4 remaining...



As far as failing VP-44's, a couple of recent VERY early failures seem to have occurred on significantly modded fuel systems, and when the owner was "pushing" the performance a bit - I sorta suspect a bit more low-key, easy operation to allow internal component seating and break-in would be a good idea to get longer life outta the VP-44 - pushing it too hard immediately after installation might be asking for trouble...

 

[Guest]

I solved my VP-44 problem finally, I sold it last night. Went and snagged a 325/600. I will miss the 2nd gen though, it had such a cockpit feeling with all of the gauges and sounds.

 

[Gary - K7GLD]

I solved my VP-44 problem finally, I sold it last night. Went and snagged a 325/600.



Congratulations - but be advised that even without the VP-44, your NEW truck is still vulnerable to LP failures and premature injection pump failure due to poor and inconsistent fuel quality and lubricity - don't let your guard down just because you have the "latest and greatest"!

 

[ScottWright]

Bill,

Were where were you measuring the fuel flow out of the vp44 was it after the head drain "T". Seems like on other threads no matter what PSI was put on the input side the output was never more then 30gph. The pump is internally restricted above that point it seems? Were you measuring the return off the FASS at idle?

 

[jarsong]

Comes down to you need FLOW, not pressure. I guessing you could have ZERO pressure but as long as the pump could still "suck' enough fuel you'll be fine until your next filter change and you can't refill the thing. Try blowing Honey through a straw once. LOTS of pressure, but nothing coming out the other end. Lift pump bypass with a check valve to stop reverse flow might be a good bomb.

jarsong

 

[Texas Diesel]

IMO, besides the obvious LP failures and tapped wires, low fuel lubricity is worth considering.



I had a copy of a Bosch Syposium (SP?) on injection pump failures, the main jist was that the problem cut across OEM lines, product lines and applications. Basically the problem was across the board and the conclusion was (basically) that lowering lubricity due to low sulfer EPA fuel was the underlying cause of the majority of failures.



Another member here with one on the early VP-44's (one of the bad ones) had at last count 250k on his VP-44 with no problems. At every fillup he added 2 cycle oil to his fuel.

 

[Stefan Kondolay]

I feel like I am somwhat of an expert as they call me the pump killer around here. You can add 3 more things to your list , this is what we learned in our testing of the RASP pump system. Not all electric lift pumps are created equal. A lot of the lift pumps will allow fuel to drain back overnight. That is why a lot of the time when a guy bumps the starter some lift pumps will run for about 20 seconds some will run for about 2 seconds before shutting off.



We found the higher the fuel pressure , the greater the heat. Even with the RASP system we were only using # 6 line to feed it as that was all that was required. The only time we used the # 8 line was when the guy already had the existing # 8 line.

 

[jarsong]

Hey pump killer, Does the stock pump have some sort of check valve to stop the reverse flow?

jarsong