Lets discuss how the in-tank lift pump module works

[brods]

I was looking over Richard Martin’s article on the Glacier website about the Dodge in-tank lift pump ( http://www.glacierdieselpower.com/images/PDFs/IntankPumpExposed.pdf ) and several questions come to mind. The main question is given the OEM’s drive to cut costs and simplify things, why does the in-tank pump module look so complicated? I’m not interested in debating if the design is good or bad, just curious how exactly the assembly works.



Most of the design appears pretty straight forward, except for purpose of the venturi and flapper. I’m guessing the venturi and flapper valve are designed to keep the fuel reservoir or bowl, which the pump is mounted inside, full and overflowing when the level in the tank is below the top of the bowl. This would keep the entire pump submerged, maybe for cooling purposes? Is its purpose to prevent the pump from sucking air while the fuel level in the tank is low and the fuel sloshes back and forth while driving? Both?



Any other ideas what the venturi setup would be for?



It is hard to tell what sort of screen there is under the flapper valve. Does anyone have a picture of the underside of the fuel bowl showing the screen where the fuel goes in?

 

[jelag]

I installed this conversion in an 04 and just had it out for failure to function... . the cause of the failure was a crimp on a DC wiring harness that came in the kit... . the wire broke off the connector and the pump quit with no power... This system is like any other in tank pump... the fuel enters through a screen in the bottom of the assembly through 1/8" square holes and passes through a screen... . into the suction side of the pump... attached to this assembly is the float for the fuel level... there is nothing special about this... . I've found the supplier off shore who makes it for DC but have yet to order some in... the one I installed on my 04 has been in service over 100K miles and except for the crimp on the wiring harness has worked well... the truck had and aux. lift pump on the frame to extend the life of the old engine mounted lift pump... that didn't work... . it still failed... we tried to pull fuel through the new, in tank pump with our frame mounted lift pump but it wouldn't work so we took our pump out of the circuit... .



I think this pump is a winner... I also own an 04. 5 and a 05, the 04. 5 will get the new in tank pump in the next 6 months and we haven't had a problem with the 05... .



Hope this helps. .

 

[sag2]

To answer the question the bowl and flapper are there to keep the pump from running dry, especially at low fuel levels. The return line from the engine flows directly into the bowl to also keep it full and primed. Some also have a venturi to help pull more fuel into the bowl. These pumps will pump fuel with almost no fuel left in the bottom of the tank. The bowl actually has a higher fuel level than the tank when it is running, sometimes several inches higher.

 

[TMoe]

That article mentioned a bypass set at 8 psi and an internal pump bypass of 19 psi. I wonder what the pump flow chart looks like. I also wonder how the return fuel affects the bypass function, pressure setting, as they are connected together. Probably not at all. Is the bypass spring adjustable for more flow since the internal setting is 19 psi? I am glad to start hearing some positives on this pump. I also think the fuel line from the pump to the engine mounted filter is small and could be increased to 3/8 hard or soft line to help if needed, more hp, aftermarket filter install, etc. , in addition to banjo bolt ellimination. Manual states this pump must be purchased as an assembly. How much is it? I found in web search, under collision fuel system, a 2006 fuel pump, 5. 9 for around $130. Is that for the whole assembly? Not bad if so. The reason I ask is that non engine related parts that tend to fail post warranty on these trucks, steering gear, steering pump, etc. , aren't that unreasonable with dissount for the do it yourselfer vs $1800 I am debating to spend on 70,000 mile extended warranty. I think I will pass on the warranty since I do all my own work anyway.



Good advice for cooling and in-tank pump operation, keep your fuel tank filled up!

 

[brista]

The return line from the engine flows directly into the bowl to also keep it full and primed.

That is interesting, so it dumps the hot fuel return into the bowl where the pump sits. I thought one of the reasons the pump was put in the tank was to cool it?



Great info in this thread.

 

[mhenon]

That is interesting, so it dumps the hot fuel return into the bowl where the pump sits. I thought one of the reasons the pump was put in the tank was to cool it?



Great info in this thread.

It does return the hot fuel to the bowl which is meant to keep the bowl full. There is an aux return on this pump which would dump the fuel outside the bowl. I'm thinking of running this return for summer use and going back to the regular return for winter. With the VP44 IP hot fuel is not too good.

I left the intank module in place and it's working as a pusher to feed a frame mounted Carter LP. It works perfect (so far) for this and I was getting 26psi until I added a bypass valve to regulate the pressure to 15psi. My system goes from the intank through a 20 micron filter/water separator, to the Carter LP, a 2micron filter and then the VP. The bypass is between the carter and the 2 micron filter.

I purchased a spare intank module with the intention of modifying it to get more pressure. After looking it over i came to the conclusion it was better to leave as is (other then using that aux return) and building the system up from there.

One more thing. I have a switch in the cab so either pump can be run independent of the other. The intank has no trouble pushing fuel through both filters and the Carter and building it's usual 5-8psi. The Carter, on the other hand, can suck fuel through the intank. . but you can here it struggling (cavitation?). Think I could limp home on the Carter alone but not sure how long it would run.

Mike

 

[TMoe]

Just how hot is the return fuel? How much is used to cool injectors, vs. returned directly from CP, out of the 1 GPM supplied? Please point me to info on how fuel is used for cooling as manual states excess fuel not burned is used for lubricating injectors. How much is in the in-tank bypass that also returns and isn't heated? And finally how much of the return fuel actually gets recycled directly back to engine? Presently, I can't believe, other than for very low tank conditions, this would be a concern. Just trying to stir the pot! :-laf There is a heater in the fuel filter canister that only operates above 70 deg F ambient I think.

 

[mhenon]

I think you're right. Low tank conditions are where you would see hot fuel. It also gets kinda frothy, as Richard describes, from the venturi tube on the bottom of the unit. This is probably why I saw fluctuating fuel pressure on a low tank.

With this type of pump/bowl I would try to keep the tank above the 1/4 mark if at all possible.

Mike

 

[Dieselnerd]

Brods, good info. Thanks for the link to how the pump works. The '05's have been out long enough to have pump problems and I'm not seeing much about pump failures yet. Maybe we finally have one that is fairly reliable.

 

[brods]

Has anyone actually seen the fuel module operating under real world conditions? Reason I ask is because of the frothy fuel comments. Running the fuel module in a bucket and not restricting the discharge flow rate to the same as what it be on the truck, may not give an accurate picture of how the setup works. Too much flow diverted away from the venturi will diminish its effectiveness and could allow the level in the bowl to be lower than what it would be in real conditions. If the bowl is full, I would think there is less likelihood there would be all this frothiness.



Anyone know what type of pump it is? Like a gear rotor type?



Tmoe, some good questions on heat. I hope this assembly was tested in all extremes of temperature, etc. by the Dodge engineers before they signed off on it for our trucks. Maybe in the heat of summer and pulling a heavy trailer it might be wise to stay above a 1/4 tank, but for the rest of the year I do not think there would be any heat issues on a stock truck.



I always run the tank way down before filling up and have yet to have a problem in any vehicle (knock wood), but if the bowl really does have foam, meaning the fuel is getting aerated, anytime the tank is lower than a 1/4 full, I will definitely change my re-fueling habits!



Good info, thanks guys!

 

[TMoe]

One final comment on the GDP article. It states most of the flow is going into the venturi making it sound like wasted pump output. The venturi feed may be a separate pump section (?) but the point is that fuel under very low psi will not take much energy at all and is therefore not really affecting pump life, in my opinion. Also drawing in extra fuel, to supply venturi, will ensure hot returned fuel is mixed with plenty of non-return fuel from bowl or tank. So, if 1 gpm or so is going into engine and 1 gpm or more is going into venturi and some additional fuel in bypass that makes over 120 gph. That seems like a very high output pump. Keeping the pump output pressure low at 8 psi will increase life of pump, less current, heat, etc. , and that is what Dodge is trying to accomplish with factory set up. The CP only needs positive pressure, above 0 psi, to work, from what I've read on other posts. Some have mentioned keeping it above 3 psi or so. I hope Dodge did the engineering and designed this pump and didn't simply choose an off the shelf existing pump that was good enough. I am feeling more confident in this pump, whether real or not, I will feel better not worrying about it. I am being much more selective on mods with the new truck as I simply dumped money into anything anyone recommended on the 01 from the T-steering to the 3rd gen trackbar to the PSC gearbox, etc. , and didn't need many of them. Funny how the new trucks steer and track so good with that crappy Y steering set up.

 

[mhenon]

I always run the tank way down before filling up and have yet to have a problem in any vehicle (knock wood), but if the bowl really does have foam, meaning the fuel is getting aerated, anytime the tank is lower than a 1/4 full, I will definitely change my re-fueling habits!



Good info, thanks guys!

I can only tell you that my pressure started to bounce around right after the fuel light came on (well below 1/4). There's probably nothing wrong with running the tank down before refilling but I wouldn't recommend constant driving on the lower 1/4 of a tank.

My opinion is this is a stout little LP and provides a nice boost to the main fuel system. It's also in the right place; bottom of the tank surrounded by cool, lubricating fuel. By any standard it should last.

It doesn't provide enough fuel pressure for the VP44 (5-8psi) but may be all that's needed for the CP3.

Mike

 

[GTani]

I have a 2004-1/2 with the stock lift pump in the engine compartment. I can't locate a stock lift pump of this type. I would like one as a spare. So if anyone who has changed over to an after market pump and has one sitting around I woud like to buy it.

Thanks

 

[brods]

Tmoe, though I don’t feel all the comments in the article are unbiased, I do thank Richard for posting the informative article and pictures on his website. Maybe his perspective is more towards performance potential rather than plain stock effectiveness?



Mike, imho your setup has probably changed the system’s balance to where it is not a accurate example of a stock system. Here’s my reasoning. (I do not know the real flow rates so I’ll use made up numbers without units for the example).



Say the stock fuel module is rated for 10 units of flow to the engine. Say the pump produces 20 units of flow, 10 for the engine and 10 for the venturi. The stock system has the tube sizes and bypass setting so that everything gets the right amount of flow. Your booster pump will change the balance of things by sucking more flow out of the engine side of the module so the flow to the venturi will be reduced. With your booster pump ruinning, say 15 units will go to the engine (and the extra flow back to the bowl via your bypass valve) which leaves only 5 units for the venturi. So its very likely the venturi will not be as effective as it would without the booster pump. And since the venturi is what pulls the fuel from the tank into the bowl, the fuel level in your bowl may very well be lower than if you were using a plain stock setup, making the pump more likely to suck air causing the pressure to bounce around. Just an idea.