Need help with lift pump sump, nowhere to install
- Thread starter pavetim
- Start date
I could never understand the appeal. the stock pickup can extract to less then a 1/4" of fuel left in the tank without adding much air to the fuel. the sump if used down that far can easily suck air just from the sloshing. in a static environment sumps would likely do best but not in a moving vehicle. not to mention the damage risks and legal issues
The LML pickups do not flow as well as the older ones, and the older ones are prone to efficiency losses as well. All but 1 lift pump I've installed in an LML required a sump to keep the pump from cavitating. Call Fass and they'll tell you the same thing.
Think about it for a minute. With a sump you will have a lot less room for the fuel to move around in. Less likely to slosh out, and rapidly refilled when the fuel sloshes back to the other side. This would only be a concern when close to empty. And when moving at a stable rate, it's the same as sitting still. Now a sustained negative g force will empty the sump, but then you have much worse problems.
Imagine a gallon milk jug with a thimble sized sump in it.
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FASS is also the only pump ive ever seen that requires a self prime but you call them and you are the idiot that says so. airdog has no issues self priming or issues on a LML
fare points. at what HP or fuel draw does this become an issue?
the stock pickup has it's own bowl that does the exact same thing except it's taller and resists loosing the fuel better than the sump during acceleration or steep grades. not seeing your logic
the point hes making is that the factory fuel sump is superior over the aftermarket. it has trap doors to keep the pickup submerged under fuel and teh sump size is double the size (or more). in your instance, you can cavitate the pump on a low fuel state because the sump size is small and the lift pump can drain it quick. the factory sump is far less likely under the same conditions due to the trap doors and much larger "sump".
I would think the one exception would be with the S&B aftermarket fuel tank. That one is designed to have a sump added. The bottom of the tank where the sump would go has some raised areas around the sump would mount. I was thinking the LMM and LML were the two Duramaxes that had the biggest problem with 1/4th cavitation issues. While some have been successful with the factory sump with some of the larger capacity lift pumps available one of the simplest solutions is running the base line lift pump from FASS or AD. The FASS 95 or AD100 can easily support up to 600HP which will cover 95% of trucks that are out there. When running the larger pumps you tend to drain the basket in the factory sump faster that was fuel can flow back in. Not a problem above 1/4 tank fuel levels but once you get to the top of the basket you have to rely on the sump holes and check valves in the basket to allow fuel in. When running the 165 GPH pumps this can be an issue because you suck the fuel out quicker than what can be flowed back in. Also the return fuel from the lift pump dumps into the fill hose for the tank which is located directly above the factory sump. So when the tank gets below the 1/4 level what fuel is added back by the lift pump is usually pretty aerated adding to the cavitation issue. Dean
To me, at least, the only reason to install a sump is for high-hp applications where the factory pickup just cannot be modified to meet the needs of the fuel system. IMO, there is absolutely no need for it on a stock or even mildly modified truck.
Well cannot just push up the basket cause that throws off level sensor off. Well I already have the hole drilled under stick pickup and I need to change fuel level sensor anyways plus I just dropped a 7mm socket in the fill port lol. In process of tank removal now and will modify stock pickup so the sump goes right inside it
if the level sensor is bad, you can always install a universal fuel level sender #3262 in place of the original sender so you don't have to modify a good working pickup/sender.
I've had one in my truck for the last 6+ years with zero issues. put it on when my gauge was showing 1/4 tank when it was empty. traced it down to the sender. spliced the wire from the original sender inside the tank so I didn't have to modify the harness. only had to drill a 3/8" hole in the top of the tank for mounting. left the original pickup in place but removed the sensor and arm. this would also keep the sensor from being affected by being lifted up because of the sump
What do you mean by "self prime"? I haven't had an issue with filling and priming a Fass system since they switched to their "signature series" pumps. Before that, yes, they cavitated easier and usually needed either a full tank of head pressure or some fuel in the filter to create enough suction to get going.
I have put a couple dozen Fass pumps on sub 550hp lmls and only 1 truck, a 2016, did not require a sump in order to keep the new Fass pump happy. As far as the older ones, a lot of dyno HP has been made with a big single lift pump and factory pickup. Over 1000hp but unsure how much over. The losses I referenced are due to the poor materials and construction to withstand long service life in their environment and/or a service life at double the vacuum of the factory design. Also, for an engine that is making 500+hp and being abused by design standards, and returns its fuel much hotter than factory standards, returning that fuel to the pickup bowl to be reused immediately is not helping.