Engine/Transmission (1998.5 - 2002) I have new info on 24V LP issues...

[BobMay]

Thank you guys I was able to purchase 2 pumps from http://www.hoeslidiesel.com/specials.htm for $139 each. Can't belvie my local dealer wanted $389 for one pump.

Bob

 

[NoSeeUm]

you guys keep talking theory,I have seen most of these scenarios on a regular basis. Electric pumps will fail,period. If a stock pump on an 03 fails the pusher may not be able to push enough fuel through it to run. The same with a 2nd gen if the pusher fails the stock pump will not get you down the road with any certainty. If the in tank pump fails the pusher will not be able to pull enough fuel through it to run properly,in some cases it will be a tow-in. The only question is when, not if. Even the Rasp has issues... ... ... . do not put too much tension on the belt. The Fass has its own issues as well. There is no perfect set-up. Some work longer or better than others. I love fixing the trucks that belong to the engineers,they have all the theories but gee they still come in on the hook :-laf :-laf :-laf



Bob

Well its not really theory. But you are right. No doubt, the LP is crap or what it is expected to do it is the wrong application. Crap is crap, people make a living off of the failures. I'm on my third LP at 35k. And yes, it is fun to tell engineers "I told you so".



I do buy into the "volume" not just "pressure" idea, but if the LP pump is crap to begin with then this just all just lip service anyway. The in tank one is not that much better IMO.



This is because, it is hard to measure the volume required by the VP. So VP suction pressure has to be used. As long as there is pressure right at the VP suction there should be a capability of surplus fuel delivery provided by the LP. Nothing else really matters, pipe size nor LP design.



The VP is a variable speed positive displacement pump and it will pull what fuel it needs. If it can't, then it will eventually eat itself. Bad is bad, not to mention it is lubricated by fuel. Big surprise here.



I do know that the VP will run at zero (or below) suction pressure because mine did, but I don't know for how long. I had just installed the gauge after reading some TDR. The pressure would go to 5 psi while cranking and smack down to zero when running. However, the truck ran just fine. I vented and fooled with the gauge for an entire afternoon until "Knock knock, Hello" it was not the gauge finally sank in.



I do like the idea of a submerged pump, except for having to replace one which is a big PITA. At least the pump does not have to pull fuel through a probably too restrictive suction line. But the idea of zero pressure at WOT really bothers me about the life span of my VP after my warrantee is up.



If the stealler wants to do the in tank change on my next LP failure, I won't go along. Mounting the LP close to the fuel tank and have it push vice pull is the design I think I will go with. I am already purchasing the necessay materials for when that day arrives.



Jim

 

[BobMay]

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[steved]

This is because, it is hard to measure the volume required by the VP. So VP suction pressure has to be used. As long as there is pressure right at the VP suction there should be a capability of surplus fuel delivery provided by the LP. Nothing else really matters, pipe size nor LP design.



The VP is a variable speed positive displacement pump and it will pull what fuel it needs. If it can't, then it will eventually eat itself. Bad is bad, not to mention it is lubricated by fuel. Big surprise here.





Jim

Jim: We do know the requirements of the VP44, 15GPH burned and 30GPH returned to the tank for a total of 45GPH at max.



I guess theoretically, if a gauge is reading 0psi (and not vacuum) then the LP is supplying enough fuel to the VP... it is just doing so at it's max volume with no reserve per se. I remember someone stating that the VP-44 recommended inlet pressure is between 12-14psi... at what point we don't know (idle, 2000RPM, or WOT???) which the intank pump is far from supplying from what limited info I have seen regarding pressure.



I do think that treating the intank pump as a "booster" is a great idea... other than being inconvienient to change when it fails, it makes about the best booster pump you could have (high volume/low pressure).



steved

 

[cerberusiam]

The VP is a variable speed positive displacement pump and it will pull what fuel it needs

In the Ram truck configuration it is highly unlikely it will pull enough fuel for anything off idle. In a backhoe or other use where the fuel tank is mounted higher than the pump, different filters, line size, static rpm, etc, it may be able to but there is no indication Bosch ever intended it to do so, and, if it had to it would probably severely reduce its life expectancy. It is highly doubtful either Bosch, Cummins, or DC intentionally engineered but it definitely suffers from the differences between design and practical application.

I guess theoretically, if a gauge is reading 0psi (and not vacuum) then the LP is supplying enough fuel to the VP

That should read "if a gauge is reading 0psi (and not vacuum) then the VP is using all the fuel the LP is supplying". If the VP wasn't using all the fuel then there would be pressure building up. Whether or not it is enough is where the debate begins. Given the volume is enough 0 psi would be acceptable, just not in the configuration that is found in these trucks. Without the 10+ psi there is not enough flow to provide the VP with fuel for injection and lube/cooling functiuons due to the line size, restrictions, tank location, etc. The injection event is primary and the circulation is second. When supply volume equals required volume, 0 psi, fuel is pulled from circulation to supply the injection.





The pressures required to keep the VP happy, while not being very scientific but developed in actual application, are a minimum of 8 psi at WOT and 16 psi at an idle. The VP will live outside those paramters, and probably for a while, but these pressures seem to produce enough fuel at the pump for longevity.

 

[steved]

The VP is a variable speed positive displacement pump and it will pull what fuel it needs

In the Ram truck configuration it is highly unlikely it will pull enough fuel for anything off idle. In a backhoe or other use where the fuel tank is mounted higher than the pump, different filters, line size, static rpm, etc, it may be able to but there is no indication Bosch ever intended it to do so, and, if it had to it would probably severely reduce its life expectancy. It is highly doubtful either Bosch, Cummins, or DC intentionally engineered but it definitely suffers from the differences between design and practical application.

I guess theoretically, if a gauge is reading 0psi (and not vacuum) then the LP is supplying enough fuel to the VP

That should read "if a gauge is reading 0psi (and not vacuum) then the VP is using all the fuel the LP is supplying". If the VP wasn't using all the fuel then there would be pressure building up. Whether or not it is enough is where the debate begins. Given the volume is enough 0 psi would be acceptable, just not in the configuration that is found in these trucks. Without the 10+ psi there is not enough flow to provide the VP with fuel for injection and lube/cooling functiuons due to the line size, restrictions, tank location, etc. The injection event is primary and the circulation is second. When supply volume equals required volume, 0 psi, fuel is pulled from circulation to supply the injection.





The pressures required to keep the VP happy, while not being very scientific but developed in actual application, are a minimum of 8 psi at WOT and 16 psi at an idle. The VP will live outside those paramters, and probably for a while, but these pressures seem to produce enough fuel at the pump for longevity.

If the LP was not able to keep up with volume demands of the VP, then you would have a negative pressure or vaccum because the VP would be demanding more fuel than it was receiving... which in that case, yes you would be starving the pump... but at zero psi, the LP is keeping up to demand of the VP as far as volume is concerned. I am not arguing that the LP is not keeping up with the VP at 10psi, only that the LP is able to yeild enough volume to not starve the VP at zero psi... so theoretically, it is "matched" to the VP correctly... but to provide sufficient volume and keep 10psi, it is failing horribly.



And, if you read the LP thread, the VP only uses 15GPH and returns 30GPH to the tank... the 30GPH is supposedly being returned by the VP which should be the fuel it is using for lubrication/cooling?? Therefore at zero psi inlet pressure, the VP should have ample cooling and lubrication.



I believe where the problem lies is when the VP is forced to draw a vacuum because of a failing or dead LP, this then causes the VP to starve for fuel because now it is forced to pull fuel from the tank and overcome all the restrictions between the tank and itself.



steved

 

[NoSeeUm]

Thanks BobMay. Checking into that.



Thanks Steved. Since installing my pressure gauge, when the LP is working right, I always get 14-15 psi at idle and 10-11 psi or so at WOT. Reading TDR this is normal.



Jim

 

[Fishell]

Gary what did u do to get ur fuel psi up to 23psi at idle? I just installed a fass 150 gph. This is my readings that I get on my gauge. 17 psi idle, 13 psi @ 70-75 mph, but if I stomper down it will go down to about 2-4 psi. This just doesn't seem healthy to me.

 

[Davidson]

rweis, do you have a link for the RASP? Where can I get one? Thanks

 

[Bob4x4]

rweis, do you have a link for the RASP? Where can I get one? Thanks

http://www.dieseltrans.com/dodge/whats_new.htm



Here you go



Bob

 

[Huff N Puff]

You And Gary Are Forgetting One Thing.

Everyone covered this pretty well but...



If my stock lp produces 15psi and the new pump 7psi both through virtually the same fuel lines, then the new 7psi lift pump has less volume, period.



Sorry to see you leave California Gary, but I'm happy for you.

The in-tank pump is not moving the fuel through the same lines. It has eliminated a whole section of a very restrictive suction line. It is now sitting on the bottom of the tank. It does not have to draw the fuel through 6ft of very restrictive fuel system and then push it to the VP. If either of you had ever pulled a 2nd gen. fuel module out of the tank you would see why you cannot improve the fuel delivery unless you open up the fuel module first. This is why Mopar tackled this nagging issue from the source IN THE TANK.

 

[Learguy]

H&P, Do you have the dimensions of the new pump, lines, etc... . ? I have the in-tank, don't want to drop the tank just for exploration.



TIA

 

[Huff N Puff]

The in-tank pump does not have a suction line

H&P, Do you have the dimensions of the new pump, lines, etc... . ? I have the in-tank, don't want to drop the tank just for exploration.



TIA

That is why it can move more fuel with less pressure. Hope thats the answer to your question.

 

[Huff N Puff]

Its not

Gary what did u do to get ur fuel psi up to 23psi at idle? I just installed a fass 150 gph. This is my readings that I get on my gauge. 17 psi idle, 13 psi @ 70-75 mph, but if I stomper down it will go down to about 2-4 psi. This just doesn't seem healthy to me.

Your 150gph pump can supply the VP with plenty of fuel at idle. So the pressure backs up to 23psi. At WOT your 150gph pump can only supply 25gph cause the fuel module plumbing has only about 1/4in feeding your pump. Your pump is rated at 150gph with a 1/2in supply line. It cant move enough fuel through the restrictive fuel module.

 

[CFAR]

So with the in tank lp replacement, the fuel module and 6 ft of line (up to the fuel filter?) is replaced?

I have the common 7 psi at idle, 5 psi cruising, 0 psi wot readings

If you have positive pressure @ wot then you can be virtually assured you are supplying enough fuel to the vp44.



If on the other hand you have 0 psi or negative pressure, then you are not, regardless of fuel line size, because as you stated earlier :

Your 150gph pump can supply the VP with plenty of fuel at idle. So the pressure backs up to 23psi. At WOT your 150gph pump can only supply 25gph cause the fuel module plumbing has only about 1/4in feeding your pump. Your pump is rated at 150gph with a 1/2in supply line. It cant move enough fuel through the restrictive fuel module.

 

[mhenon]

That is why it can move more fuel with less pressure. Hope thats the answer to your question.

What's the reason it moves more fuel with less pressure??? My fuel line diameter hasn't been changed. It's just that the in-tank pump is at the beginning of the supply line. . not the tail end of it. And, I agree, this is a good thing. I just don't see how you can say more volume of fuel is now moving through this line.

When I still had the OEM LP on, I use to bump the starter and then go open the drain valve on the fuel filter. Just wanted to check the flow once in awhile. I did the same test when the in-tank pump was installed. I can assure you it isn't putting out anything close to the old Carter pump.

But, it might not matter. Having the pump in the tank and pushing fuel may solve most of the LP problems. My old F-150 has over 190,000 miles and the in-tank pumps are still working fine. Never had to replace it (them... dual tanks). This says something about letting the pumps "push" instead of "pull" fuel through a given length of line.

I like Bob's idea of a dual/parallel fuel system. That along with the "Fedex" VP44 (heavy duty electronics) and you might have a fairly reliable fuel delivery sytsem.

Mike

 

[nps]

What's the reason it moves more fuel with less pressure??? My fuel line diameter hasn't been changed. It's just that the in-tank pump is at the beginning of the supply line. . not the tail end of it. And, I agree, this is a good thing. I just don't see how you can say more volume of fuel is now moving through this line.

Mike - agree 100%. The theory doesn't hold water since you are measuring pressure after the pump. If the new pump put out more volume, you would see more pressure developed as a result.



This intank pump is good, but if you believe some of the VP44 rebuilders that claim a minimum FP of 7 psi is needed on the VP44 inlet diaphram to prevent excessive movement and cracking, then the stock LP or a frame-mounted pusher is still needed to get the FP back up.

 

[Allnew2Me]

1 2

 

[Learguy]

That is why it can move more fuel with less pressure. Hope thats the answer to your question.

H&P, Thanx for the theory(?) Do you have dimensions????? Not Theory.....

 

[Huff N Puff]

H&P, Thanx for the theory(?) Do you have dimensions????? Not Theory.....

I'm not confused at all,There is no suction line on the in tank pump. How can I give you the dimensions of lines that don't exist. The opening of the inlet of the intank pump is about 3/4in. The inlet of the fuel module that feeds the old lift pump,inside diameter is a little over 1/4in.