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Discussion Starter #1
Been fooling around with some pre and post filtration ideas and models and was wondering about pressure ratings for lift pumps. I've got one in mind that has between 4-9psi, but need some input especially since someone posted the "GM said lift pump will void warranty blah blah". It got me thinking about the consequences of adding a pressure to a vaccuum system. Does there need to be a pressure bypass (I found something breifly about that, but couldn't track anything else down, probably subject illiterate
), possibly fed into the return? And if that's the case, how much pressure does that add to the return line or does that eventually matter to the pump? As always, ideas are welcome. Thanks
 

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IMHO some form of regulator would be better than a bypass. I don't think that a bypass would raise the pressure in the return line as one end is completly open (isn't it?) at least I think there is no restriction. The problem with a bypass is ensuring that you don't go back to a vacuum system when fuel demand is at it's highest. I am unaware of a suitable regulator although I'm sure there must be one; I don't know of it. As far as warranty, I've heard Dealers say that they have to perform ALL maintenance on a vehicle to protect it's warranty. Point being that a disreputable Dealer will say anything to improve his profit margin.


BTW, welcome to the forum
Edited by: a64pilot
 

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I hear Dodge uses a lift pump on the new Cummins with the same high pressure common rail pump used on our trucks. I do not believe low pressures would hurt the pump. Just curious what it might do to the pressure control valve's ability to control rail pressure. It may not be an issue at all, just one to keep in the back of your head.

a64pilot,

Are you saying there could be an issue with return line pressures possibly leading to leaks? That would be another cudo for the LLY external injection setup.
 

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a64pilot...I was under the impression a bypass would keep continual flow until it was desired. Same thing they are doing with the needle valve. The return line doesn't have any restriction, on a bypass designed regulator, but it isn't supposed to. I believe the needle valve method will still have some pressure present in that line though.


A return line is supposed to be un-restricted and return to the tank...not to the feed line. I thought this was also a better way to keep the pressure off the pump and increase cooling while extending pump life.


On edit....I don't understand why you would want pressure on the return line.


GeorgeEdited by: BIG DIPPER
 

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Red Fuel,
Sounds like you are doing your homework.
In addition to what you will find here there is also volumes of info on lift pumps over at The Diesel Page Duramax Forum. I did a search over there on “Lift Pump” and it returned 112 hits.
Here’s two threads with some good lift pump pressure info:
Lift Pump Pressure
Lift Pump with Pre-filter
2 Lift Pumps
My lift pump setup uses the AC Delco EP158 with a “bypass regulator” loop that includes a needle valve to adjust the pressure at the Schrader valve test port (near the alternator) for approx 0 psi at idle. The lift pump is primarily to eliminate vapor build up in the post OEM (Mega) filter caused by vacuum/heat induced out-gassing of the fuel. Those with pre-OEM filters on the frame rail (or post-OEM filters mounted in the Lone Eagle position above the PS pump) haven’t had problems with vapor build-up. However, when operating the filters in a vacuum they may not be fully covered with fuel (see Suction/Vacuum Side Fuel Filters for more info). Other benefits I've noticed from the added lift pump are fully utilized fuel filter surfaces, smoother/quieter engine, better throttle response and quicker starting.

IMHO, all the pump installs that have been used and discussed so far by various folks on the Duramax forums will not maintain a positive pressure at the Schrader valve test port (input to the OEM pump) under heavy load and/or hard acceleration. But, they will maintain flow and enough pressure to prevent vapor build-up in the post-OEM filters. I have thought about moving the sample point for my bypass regulator from output of the pump to a tee at the output of the post OEM (Mega) filter. It seems like this would be a more ideal point to regulate the pressure under all conditions. But it would require running another fuel line back to the lift pump.
Good luck on your setup. There are lots of good options to consider.
 

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jbplock said:
IMHO, all the pump installs that have been used and discussed so far by various folks on the Duramax forums will not maintain a positive pressure at the Schrader valve test port (input to the OEM pump) under heavy load and/or hard acceleration.
The Stanadyne FM100....you don't think this pump will keep pressure at the Schrader port under heavy acceleration? 8psi and 80 gph
 

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The lift pump I use will maintain 5psi (what I had it regulated at) at the schrader port under any condition.
 

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Big Dipper,


IIRC a TDP member tested his FM100 lift pump and the pressure did drop under load. Do you have an external bypass loop?


CPMac,


Sounds like you have a nice setup.
Which pump/regualtor are you using? Have you tested the pressure regulation under on load by monitoring at the schrader valve? Some of us have done this by hooking up the GM Kent-Moore gauge and going for a ride (gauge on the windshield under the wiper blade). JK has seen some interesting results doing this. Pressure drops even with a lift pump...


 

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I remember JK saying he could pull his lift pump under vacuum, that leads me to believe it is not big enough and is probably causing more restriction when the mechanical pump tries to pull through it. I know it is a pull through design, but it has to add restriction.


I have been searching on TDP for the past few days and found a few using the FM100, but nothing on it ending up at zero. I do not have a lift pump on yet so this is why I ask. I was beginning to think the FM100 would be all a guy needed, but after talking to a few members, I am beginning to have some doubts.


I re-read and you said drop, not end up under vacuum. I guess that could be a difference, if it drops, as long as it is not drastic, I guess it should be OK. ???Edited by: BIG DIPPER
 

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Yes Jp Block.
 

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Discussion Starter #11
Thanks fellas. I'll run through the info, put the system together, post some photos, then drink a beer. On a side note, Baldwin now has our trans filters, BT8460, and cab air filters, PA4149-kit (comes with 2).
 

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Guess I wasn't clear enough. No, I don't think you would want pressure in the return line. I don't think you could build pressure either as it's open on one end.


The bypass systems I'm aware of (needle type) are not constantly variable, they bypass the same amount as long as the pressure is constant. I.E. they don't have the ability to not bypass any when fuel demand is high, so unless you have a lift pump that has a flow rate well in excess of the max amount the engine can demand your pump supply pressure will drop and may go negative.


What I think would be needed is a high volume/low pressure pump that has a flow rate well in excess of the engines demand. A regulator would be nice IMHO to keep pressures low, but may not be necessary. It would be nice also if this pump wasn't a positive displacement type so that in case it fails fuel can still be pulled through it like it could be in the 6.5's.
 

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A64...got ya.


I think if a bypass as opposed to a regulator was used, it would make a very small chore to throw in a temporary line to get you home.....call it a Limp Mode...
. I can agree with the higher volume, lower pressure.....but we have to think about the cup that we are pulling from inside the tank..can't take it dry.
 

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Mackin I am doing a little backup research BEFORE I shoot.
 
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