Lift Pump Pressure - Diesel Bombers



Chevy/GMC 6.2L and 6.5L Discussion of Chevy and GMC Trucks with 6.2L and 6.5L Diesel Engines

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Old 03-19-2012, 03:19 PM
Diesel Fan
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Default Lift Pump Pressure

I just installed a new Carter (I know) lift pump on my 93 6.5 Turbo Diesel. Before I switched I installed a pressure gauge between the fuel filter and the IP, which read anywhere from 5 to 6 psi at idle.
Now that I have my new LP installed, the psi is exactly the same. From what I understand should it be closer to 10 to 12 psi at idle?
Its a Mechanical IP but like I said the gauge is before the IP. Is this psi ok or should I be looking elsewhere for a problem?
It also has a new fuel filter installed.
It starts great, runs at idle forever, then dies after driving a few minutes. Typical yes, but trying to figure this fuel pressure out before anything else. Thanx

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Even better....
After letting it idle at 6 psi, I ran it up and down the driveway a few times and actually got a vacuum, what?
There a no noticable fuel leaks, defiantely lost. Had to walk away for the day

Last edited by silversurfer0690; 03-19-2012 at 03:19 PM. Reason: Automerged Doublepost
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Old 03-20-2012, 12:28 PM
great white's Avatar
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As long as you have pressure, the IP will be somewhat happy.

A vacuum indicates the pump is not working or not working up to snuff as the IP is demanding more flow than the pump can deliver.

Not sure on mech lift pumps, but the numbers you quoted (IE: 10 psi) is more like what an electric LP puts out.

Guys get all wrapped around the axle about PSI, the important thing is flow (IE: GPM, GPH, etc) but that's a bit harder to measure so it's referenced off PSI....
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Old 03-20-2012, 10:56 PM
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Thanx Great White!!
U misread a lil, I was said my IP was Mechanical but of course my LP is 12V driven.
And yes, I completely understand we shouldn't get to hung up on exact LP psi, but maybe to explain it a lil better;
The LP is brand new out of the box, yes a Carter but it is reading the exact same readings as the older LP I took off. Exact same symptoms. Today I put a brand new OPS on, but it changed nothing.
So further, I dropped the tank, and empty all fuel, sock on the sending unit is great shape, to see if the was any obstructions in the tank. After letting the fuel set to seperate, very lil sediment, but a good percentage of fuel was actually water.
Would an excess of water cause a pressure drop? Tomorrow plan to re-hang tank change some hoses and see what happens.
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Old 03-21-2012, 09:10 AM
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I installed a mechanical fuel gauge between filter and pump and it read 11 psi .. under load it went down to 6-7 .. the lift pump was changed out 7 years before so I installed a raptor 100 and the preshure at idle was 17 psi and under load 11-12 psi hope i didn't waste money
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Old 03-21-2012, 09:33 AM
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Sounds like a plugged line before the lift pump. Check for a smashed hard line or a collapsed rubber line. The rubber line may be hard to see since the core can separate and collapse.
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Old 03-21-2012, 10:27 AM
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Quote:
Originally Posted by dieseldanny View Post
I installed a mechanical fuel gauge between filter and pump and it read 11 psi .. under load it went down to 6-7 .. the lift pump was changed out 7 years before so I installed a raptor 100 and the preshure at idle was 17 psi and under load 11-12 psi hope i didn't waste money
that sounds good to me, on a ds4 IP you want 11-15 psi at idle and 6-7 under load
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Old 05-01-2012, 03:44 PM
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Quote:
Originally Posted by bftrain View Post
Sounds like a plugged line before the lift pump. Check for a smashed hard line or a collapsed rubber line. The rubber line may be hard to see since the core can separate and collapse.
Hi, I think I have one of these rubber fuel lines collapsing & robbing me of fuel pressure. Where can i get a new one?
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Old 05-01-2012, 04:03 PM
ebarresi5894's Avatar
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Old 05-01-2012, 05:56 PM
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Its not hijacking a thread to ask where to get a new fuel line, when I have the same probable, you ***.

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Last edited by kayakguy7; 05-01-2012 at 05:56 PM. Reason: Automerged Doublepost
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Old 05-01-2012, 08:51 PM
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Quote:
Originally Posted by dieseldanny View Post
I installed a mechanical fuel gauge between filter and pump and it read 11 psi .. under load it went down to 6-7 .. the lift pump was changed out 7 years before so I installed a raptor 100 and the preshure at idle was 17 psi and under load 11-12 psi hope i didn't waste money
You need to turn the raptor down!

They can build much more pressure than the ip can handle.

There is an adjustment screw on the side of the pump body.

If you bought the kit for a 6.5 it should have come pre adjusted for about 8-10 psi.

Much more than that and you're risking the seals inthe pump and possibly ending up with fuel in the crankcase.

How do I know?

Well:



I run one on my 1998.




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