Cummins lift pump with 975-1 or 975-3 comp can valve spring. Anyone have this mod don

Jeffrey Weeks

Jeffrey Weeks

New member
How do you like it? Did you notice significant added fuel pressure carrying through higher Rpms? Looking to get more fuel out of my stock lift pump. I do have a pusher pump also.


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Running the modded stock lift pump only on my truck with 1/2" lines. somewhere around 700hp and no issue keeping over 55psi line pressure.
 
I'm running the stock lift pump with 1/2 inch lines from the tank to the pump. For me the big lines were the key to maintaining 50psi higher up in the rpms
 
I did both with no luck. I also enlarged the holes in the piston itself to allow for quicker fill but no luck. I run 1/2 lines and a sump. Must be something wrong with either my lift pump or injection pump. Can hold 50 psi idle and free rev. Wot by 3k rpm it’s 10 psi, not performance. My current solution for this situation is a new 13mm pump and aeromotive a1000
 
I could drain a stock lift pump with a sump and big lines down to like 5psi, I'd have to see this to believe it, with a healthy ppump anyway.
 
ctdthrasher said:
I did both with no luck. I also enlarged the holes in the piston itself to allow for quicker fill but no luck. I run 1/2 lines and a sump. Must be something wrong with either my lift pump or injection pump. Can hold 50 psi idle and free rev. Wot by 3k rpm it’s 10 psi, not performance. My current solution for this situation is a new 13mm pump and aeromotive a1000
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Do you have a sump or sucking fuel thru stock screen in the tank? Tank screen will plug or hinder fuel flow.
 
jasonc said:
I could drain a stock lift pump with a sump and big lines down to like 5psi, I'd have to see this to believe it, with a healthy ppump anyway.
Click to expand...

Did you put the stiffer spring in the pump? Brand new pump? Did you get a less restrictive prescreen and bypass the heater/strainer all together? Bigger fittings going into the pump? The whole works?
 
After installing spring, and resealing my pusher pump. I can now get it to hold 75psi at 2k no load, I'm waiting to be able to give a WOT run and see how it holds. All 1/2 lines from fuel cell.
 
ctdthrasher said:
Beans sump. Just one filter before the lift pump, which may be an issue since these pumps don’t suck well??
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You can't run a filter ahead of the lift pump, it's to restrictive.
You need some type of low restriction pre-screen ahead of the lift pump

Here's a photo of the Racor PS120-1 pre-screen I installed on my Fummins.
It rated at 120 gph and has 1/2" fittings
Racorstore.com has them in the misc filter section for around $65

DSC00485.jpg
 
I have the 973-1 spring in a brand new cummins lift pump, pre heater/bowl removed, 140 gph pusher.

The spring helped a bit. I don't have to turn the pusher on for passing somebody , short bursts etc.

With the pusher turned on it was holding 20 or better 0-90 mph. Idles at 66 without the pusher, cruises at 50-60.

Stock lines and having the pusher in line with the factory lift pump probably doesn't help. I want a sump to either feed my pusher or the lift pump, 1/2 lines and a checkball/t like the junker drag truck. I took my neighbor for a ride today and almost starved it bad enough to kill the truck. I launched harder than I ever have before today at 2300 in 4hi at around 20-25 psi with the 71mm. By 80 it was laying over from lack of fuel I think. I didn't keep an eye on the fuel pressure gauge but I assume launching it at higher boost and rpm put more strain on the weak fuel system. It's good enough to leave black marks for 15-20 feet in 4hi :)
 
It was turning 3300+ rpm when it starved. 1st and 2nd will hit 3500+ pretty quick. Still at 19*
 
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