Loss of fuel flow

[JOCKO]

My problem with a 2002 LB7 with 82000 miles is running out of fuel in the filter during a hard pull with my 9K trailer on a hot day. My wagon just shuts down with no diesel in the filter with no limp and no codes. I was towed to a dealer where they did the flex fuel line replacement to no avail.
My local GMC diesel master informs me that my problem is that the fuel filter mounting assembly is leaking air when hot and not storing fuel. My cost for replacement is over $600.
Can anyone add to this as I find no info re: this type of problem on the DP site.

Thanks for any help

[rapidoxidationman]

I'd start with a new fuel filter (OEM with a metal can, not plastic) and make sure the O ring is properly installed.

Someone will be along shortly recommending a lift pump between the tank and filter, but in my (limited) experience as long as the fuel lines are good and there are no air leaks you won't have a problem. It's the relative vacuum between the tank and high pressure fuel pump that air leaks into.

SLIGHTLY pressurizing the fuel tank (think only a few PSI) will reveal leaks by pushing fuel out of them. See what you see on the filter housing.

[JOCKO]

My truck is bone stock with the Delco fuel filter which I change every 15K. No fuel leaks. I only have this issue when pulling on hills on a hot day.

[a5150nut]

Have you replaced the fuel filler cap recently? Could you have a gas cap instead of a diesel cap?

Or an air leak in the line from tank to fuel filter?

[Kennedy]

Adding a lift pump is a great benefit to the fuel system.

Working on publishing this:

Duramax Lift Pump

The Duramax trucks were all built without any sort of lift pump from the factory. There is no pump in the tank, on the frame, nothing. There is a hand primer pump on the filter housing, but aside from that, the transfer pump on the CP3 injection pump is tasked with inducing flow of fuel from the tank to the high pressure piston pump and then to the rails and finally the injectors. The exception here is that the chassis cab trucks with dual tanks have a transfer pump to move fuel from the rear tank to the front tank to equalize level and the vans are have a small lift pump that is used to prime the filter. In most conditions the Dmax performs adequately without a lift pump. The handicap of not having a lift pump is the tendency of leaks and restrictions in the system to cause loss of prime, reduce performance, etc. We are seeing more and more cases of no start, loss of prime, etc. due to the OE fuel filter head beginning to leak.
To put things into perspective the average Dmax fuel system restriction is 2” hg or -1psi. Under load the restriction easily reaches 8"hg and often much more under heavy acceleration and uphill. A reading of 8”hg is equivalent to -4 psi. That means whatever is outside (air) is trying to get inside with a 4 psi force. Adding a lift pump(s) to put a positive push on the fuel flips this in the opposite direction. In other words say you have 4 psi lift you have made an 8psi change in the pressure inside so now there is a 4 psi force trying to get out rather than 4 psi trying to get in. This ensures that there will be no air intrusion and if there is a leak it will show as seeping fuel.
Let's take this further.
Diesel Fuel will begin to “fizz” or “outgas” as pressures drop and temperature rises. This gas loosely termed as “air” travels to the fuel filter where it collects. This is evidenced by the appearance of a low mileage fuel filter cut open for inspection. There will be distinct color differences in the areas through which the fuel is flowing and where it is not. It will show black and white just like a dairy cow. What is happening is that the surface tension of the wetted media tends to inhibit the passing of air, but eventually it will pass, often in larger gulps. The simple act of adding a lift pump will change the filter from distinct black and white areas to a uniform shade of gray from top to bottom. This is because you are eliminating the outgassing and air collection and are now using all of the filter’s surface area. Using more surface area at the same flow rate increases the residence time making the filter more efficient at removing contaminants. This is highly beneficial to the longevity of your fuel system components
Many people report smoother, quieter operation and often an improvement in response and even a slight nudge in fuel economy just from adding a lift pump. Having the fuel pressurized and being pushed through the regulator is beneficial versus having it drawn through. Pump regulation is able to maintain transitional targets much more smoothly and precisely.

Add a lift pump to your Duramax. It just makes sense.

http://www.kennedydiesel.com/categoryresults2.cfm?Category=3&SubCategory=157

[JOCKO]

Thanks John, you the man. If I change the filter head I guess I would solve my problem, however a lift pump seems like a much better fix. If I do not change the filter head and add your lift pump will I likely see fuel leaks? Do you recommend I do both? You are now on my Buy list.

[Kennedy]

I'd do the lift pump first and see what happens. You may not have any leak at all. I'm also highly confident that adding a lift pump from day 1 prevents the leaks in the filter head.

[JOCKO]

Ordered the lift pump kit from Kennedy this morning and will report the results when tested.
Thanks for you help John
Jocko