Question on lift pump pressure- COLD

[chessy56]

Here's the setup: '01 LB7, Kennedy single lift pump, Donaldson P55-3207 filter/separator before the lift pump and a CAT UHE 319-0844 secondary filter on a billet Nicktane OEM adapter. Air temperature ~ 15 deg F, fuel temperature ~ 65 deg F (according to my Edge monitor).

My CAT UHE filter was beginning to indicate some loading a couple of months back as I was reading around 2.25psi with the Kennedy pump running and about 3" Hg without the pump (using one of Kennedy's psi/Hg gauges). I checked the pressure/vacuum this morning and was getting ~ 0.5 psi (without the engine running) and ~ 13" Hg with the engine running.

The UHE filter was replaced and I now see 2.5psi with the pump running "and the engine OFF". When I start the engine, the gauge reads about the same 13" Hg, regardless if the pump is running or not! I can hear the "whirring" noise of the lift pump when the engine is not running, so I believe the pump appears to be working.

Would cold fuel and/or a fresh UHE filter give me the results I'm seeing? The last time I checked pressure/vacuum was under much warmer conditions and I actually saw 2.5 psi with the fuel pump AND engine running! I do have a bit of Lucas fuel treatment and Power Service (white jug) in the fuel. I have NOT replaced the Donaldson filter ahead of the lift pump yet however- don't know if that's making the results look so bogus....

Any thoughts?

[chessy56]

Never mind-
Changed the primary filter and my lift pump pressure now reads ~2.75psi and without the lift pump running, I see about 2.75" Hg. All is better again.

I wouldn't have thought the primary was that clogged, but apparently so. This fuel I'm getting must really be some crap or the filling stations aren't running an inline filter on their pumps. Now I'm wondering if my UHE CAT filter was really sufficiently clogged....

[Kennedy]

#1 It's been flat out cold and a "tight" filter will have issues with marginally winterized fuels.

#2 Size is everything. I get easily 1-2 years or more from a Mega element due to it's sheer size and location.

#3 a better fuel additive or a blend of #1 fuel will help if it is simply reaching the cold filter plug point

Most stations do nothing for filtration in my experience. Filtration slows delivery, requires maintenance from qualified personnel (that do not exist on staff) and produces "hazardous" materials in used filters.

[More Power]

Fuel filters located on the frame rail beneath the truck would concern me with trucks driven in cold(er) climates. The GM diesels since 1984 have been equipped with factory fuel filter assemblies that contain an integral fuel heater, located somewhere on or very near the engine.

Back during the prototype days of the Duramax 6600, GM shipped several preproduction trucks to Fairbanks AK during the winter to test the cold weather operability of the fuel systems and general cold weather operation. These early tests showed that the fuel system was fine, but building engine/cabin heat needed more help. This is why the trucks arrived at dealerships in the fall of 2000 with factory grille covers.

Jim