Ok Gang... You all have seen the Dodge FSM book minimum pressure of 10 PSI. Well I started to do some thinging and relized even that is too low. Here lets take a look at a pic here... http://forum.mopar1973man.com/attachment.php?attachmentid=878 So now let assume your fuel pressure average is about 12 PSI which is above the 10 PSI minimum pressure. Driving down the highway at 55-65 MPH your going to be flowing at least 2-3 GPH through the pump. But now let add a twist to it. New situation... Going up to Seven Devils Campground its a 17 mile drive up a 1 lane dirt road that is steep. I'm dragging a utility trailer with 2 ATV's. Ok for the sake of the post we'll say the fuel pressure is still 12 PSI. Climbing that grade I'm going to be flowing 7-10 GPH through that pump which is a good thing because the high flow keeps the pump lubed and cooled. But now the weekend is over time to drive home. So on the way down I set the exhaust brake and put it into 2nd gear and let it limp down the rough old trail it take about 45 minutes to 1 hour to return to the highway. So now the whole way down the mountain there is 12 PSI heading into the VP44 and but now your not throttling much if at all coming down the steep grade. So this means there is no flow to the injectors... And the Overflow valve is closed because you need 14 PSI to open it. So basically there is no fuel flow. So now the electronics and the mechanical part start to heat up the stale fuel and break it down. Remember diesel fuel is a very poor lubricant anyways. So now you see this is really easy to burn up or damage a injection pump. Now I'm starting to suggest 14-15 PSI as a minimum pressure and 20 PSI as a maximum pressure. This now keeps the overflow valve open and the fuel flowing through the pump while its spining and keeping the VP44 electronics cooled... Any thought on this???

Yes , its a long trip indeed but I here it a nice place to visit ,even though I had a issue with longer cranking before the airdog install when engine is hot ? And it got worse when the airdog was installed ! Now I am hereing by the folks that installed the airdog ,thats the vp44 that needs replacing and now that the cummins folks seen it it started to be some other issue and not the VP and now that they charged 5 hundies in looking at it they they are stumped, one of the techs says it can only be the VP, is there any other way that a guy like myself with very little diesel knowledge do without bringing it in to a dealer its a $2100.00 fix at the cummins dealer using there reman injection pump ,do they go through the pumps or do they have them rebuilt by a a bosch certified tec and bench test it and replace all the componets includeing the computer,wow thats alot ,sorry and only give a 6 month warrenty .

If your truck is running fine other than the hard starts I wouldn't be thinking about replacing the VP44 until it displays more problems or just outright fails. If you are at all mechanically inclined and have access to a garage and tools you can replace the VP44 in less than a day your self. I believe there are some real good instructions on Milks web site http://articles.mopar1973man.com/2nd-generation-24v-dodge-cummins/25-fuel-system/126-bosch-vp44-injection-pump-replacement Haven't priced rebuilt VP44 in a while but I'm guessing around $1,000 exchange. All VP44s have to be rebuilt by bosh cert places unless it comes from china. I'm sure that if you started a new thread asking where is a good place to ger a good VP44 you would get lots of replies. Any VP44 you get today is a reman. You will need to know whether your pump is a SO or HO if the truck is a automatic trans it is most likely a SO pump.

thanks ,are they all bench tested and do they all come with the new updated computer ,thanks for the info I do believe I am capable of changing the vp but not without alot of input from guys like MIke and you or others that have done it before I just want to know before I start looking into a replacement if it sounds like its going bad or is there other probs that I can look at to narrow it down is there a test that I can do with vp installed that will let me know that it is a good candidate for replacement it has 152,plus on it now and its the original and I am the original owner 2wd 5 speed manual dually 3500 quad cab 24v ,thanks again i will check out the web site

thanks ,are they all bench tested and do they all come with the new updated computer ,thanks for the info I do believe I am capable of changing the vp but not without alot of input from guys like MIke and you or others that have done it before I just want to know before I start looking into a replacement if it sounds like its going bad or is there other probs that I can look at to narrow it down is there a test that I can do with vp installed that will let me know that it is a good candidate for replacement it has 152,plus on it now and its the original and I am the original owner 2wd 5 speed manual dually 3500 quad cab 24v ,thanks again i will check out the web site

If you find that you do need a VP44 take a look at this site, I've done business with him before and his prices are good. http://www.dieselautopower.com/ owners name is Jacob Kidd.

BY PHONE

951-377-4844 or 801-618-2151

BY EMAIL

dieselautopower@gmail.com

BY MAIL

Diesel Auto Power

577 N. Main st

Kaysville UT 84037 U.S.A.

This guy says it better than I can.

HARD START COLD, LONG CRANK TIMES, AND INSTANTLY RUNS SMOOTHLY

This is typically due to a cracked or broken diaphragm inside the Injection Pump. To test for this try disconnecting the electrical power from the Lift Pump BEFORE turning the key on, and see if it starts better. This happens because the electric pump pushes air which is always in the fuel chamber inside the VP44 pump, through the crack or break in the diaphragm, into the mechanical high pressure pump and it becomes air-bound until it rotates enough times to bleed out the air. If it starts better without an electric Lift Pump, it is because the electric Lift Pump hasn’t forced air into the mechanical high pressure pump through the crack or break in the diaphragm, which is what separates the fuel chamber from the high pressure pump. This failure requires a VP44 replacement to fix the problem.

25 psi was WAY too much pressure and could have damaged the diaphram. I hope this is NOT the case and and NOT the barer of bad news.

This guy says it better than I can. 25 psi was WAY too much pressure and could have damaged the diaphram. I hope this is NOT the case and and NOT the barer of bad news.

In my experiance it has always been low pressure that causes the diaphragm damage not high pressure. Because of the way the pump is built there is support for the diaphragm if the supplied pressure is to high but no support to protect it from the high pressure side of the VP if the supply pressure is to low. That is why they usually develop a tear in the diaphragm when the factory lift pump fails and is not corrected in a short time.

On my 2001 CTD Idle PSI is 18 WOT PSI is 16Cursing is 17

thanks ,are they all bench tested and do they all come with the new updated computer ,thanks for the info I do believe I am capable of changing the vp but not without alot of input from guys like MIke and you or others that have done it before I just want to know before I start looking into a replacement if it sounds like its going bad or is there other probs that I can look at to narrow it down is there a test that I can do with vp installed that will let me know that it is a good candidate for replacement it has 152,plus on it now and its the original and I am the original owner 2wd 5 speed manual dually 3500 quad cab 24v ,thanks again i will check out the web site

Not all come with a new computer. DAP sells them both ways. When comparing prices ask about the computer. Jacob Kidd will treat you right.

I'm kinda late on this conversation. I am in process of installing an upgraded pump, but. My truck had 161,000 miles on it with the original VP. I bought it with 142,000 just over a year ago. The guy I bought it from did most all of his own maintenance, but was timely. Changed tranny fluid every 15k , etc.. One thing he told me was to replace the lift pump every two years without fail and you'll not have any problems. This is not empirical evidence, but I do have 161k on the original VP. So I am suggesting that never allowing the stock lift pump to get tired may be a way around the higher pressure/volume this thread is advocating. Michael, I watched the volume pumping video. What was that demonstrating? Stock lift pump vs 150 GPH?

I'm kinda late on this conversation. I am in process of installing an upgraded pump, but. My truck had 161,000 miles on it with the original VP. I bought it with 142,000 just over a year ago. The guy I bought it from did most all of his own maintenance, but was timely. Changed tranny fluid every 15k , etc.. One thing he told me was to replace the lift pump every two years without fail and you'll not have any problems. This is not empirical evidence, but I do have 161k on the original VP. So I am suggesting that never allowing the stock lift pump to get tired may be a way around the higher pressure/volume this thread is advocating. Michael, I watched the volume pumping video. What was that demonstrating? Stock lift pump vs 150 GPH?

I will let Mike answer the last question. As for the rest you have to replace the lift pump when ever it quits supplying proper pressure. For a new oe lift pump that might be 2 minutes or who knows. A fuel pressure gauge is what you need to have. It is the only way you will ever know if the vp receiving the fuel it needs to be happy. It appears we are a little late with an answer as well.

Just to show the amount of return flow with a good 14-20 PSI supplied to the VP44...

Based on various comments above, and the wonderful picture of the internal circuitry of the VP44, here's what I think I understand:

 

1.  There are 2 different parts of the fuel circuit before the actual high-pressure part:  Lift Pump to Vane Pump,  Vane Pump to High-pressure Pump.

 

2.  There are 3 relief valves involved.  Or pop-offs, bypasses, or whatever you want to call them. 

One is internal to the lift pump, and bypasses back to the suction side of the lift pump.  This one determines what pressure the lift pump can create.

Second is inside the VP44, located at the output side of the vane pump.  It bypasses back to the inlet side of the vane pump.

Third is the one at the return or outlet of the VP44, also working off of the output side of the vane pump, but it relieves to the return fitting and goes back to the tank.

 

I've seen something that says the vane pump is putting out 250psi, and I've also seen 14.5 psi.  No idea which is correct.

 

3.  Nobody seems to be fretting about what the vane pump pressure is, nor figuring out how to put a gauge on it.  Seems like this would be the thing to monitor, since it's what is actually feeding the high-pressure pump, and it has 2 relief valves that could die and cause problems.

 

4.  Lift pump pressure is feeding the positive-displacement vane pump, and unless that vane pump is turning, there's no significant flow out the return fitting of the VP44.  So lift pump pressure has almost nothing to do with cooling the VP44, despite what almost everyone says.  In othe words, the actual fuel flow out the return of the VP44 is going to be the same with a lift pump pressure of 5psi or 20 psi.

 

Maybe a clearer way to say it is this:  At a certain engine rpm, Vane pump flow is constant.  Part of that flow goes gets dumped back to the vane pump's own inlet, part goes out the injectors, and the rest out the return fitting.

 

5.  I'm don't know why there are two relief valves on the vane pump circuit.  I guess the one that goes back to the inlet is set at a lower pressure than the one on the VP44 outlet.  Anyone know for sure?

 

6.  DDOSSDD's comment about the check valve is very interesting.  Assuming that all lift pumps are vane-type, when they crap out, the vane pump inside the VP44 can't suck fuel through them.  If there was a check valve going around the lift pump, it might save the VP44.

 

Are there some lift pumps that are turbine-style or diaphram-style?  If so, you can probably suck fuel through those.  The ones I've seen pictures of cut apart are all vane-style.

 

Please correct me if I'm wrong on any of this.