94 6.5 diesel running and falling on face

Oborowatibinast · 2025-10-04T00:23:18-0400

Hiya everyone, I have a 94 chevy c3500 with the 6.5TD and I had some questions that are kinda specific, currently battling with an issue with it running for maybe 30 seconds at a time, or less if you're driving it and falling on its face.

Ive changed the lift pump and fuel filter, but when watching the bowl fill it seemed to fill extremely slowly (the pump currently on the truck is 3-7 psi at 38GPH) I plan on seeing my fuel flow from the fuel drain tomorrow, and to do a pressure test.

To me this indicates an issue behind the fuel bowl (if im mistaken please correct me, this is my first 6.5)

There is no leaks that I can see from the bowl back, this leads me to think there's either an airlock or a problem in the tank, is there a sock on these fuel pickup tubes/ fuel sending unit that I can suspect?

Thanks in advance for any input

Tommygunner · 2025-10-04T13:58:22-0400

Yes there is a tank sock. On these older trucks it is fairly common for it to clog up. Causing the problems you describe.
When you check the drain valve. Make sure you have no air leaks. The Lift Pump should deliver at least 1/2 pint of fuel in 15 seconds. Less fuel means problems in the fuel system delivery.
If it is the fuel sock. Be sure to replace it with the proper diesel sock. Not the one for gas engines.
More info from the 6.5 FAQ sticky

https://www.dieselplace.com/threads/our-1995-chevy-suburban.637953/page-3?post_id=6620705#post-6620705

Oborowatibinast · 2025-10-05T08:21:52-0400

Thank you good sir I really appreciate the input, I'm going to try to drop the tank today after verifying the fuel flow or lack thereof, is there any good preventative measures i can take to reduce this problem in the future if it is the sock?

Haha, install a screen in the neck? Anything?

Tommygunner · 2025-10-05T12:31:14-0400

The fuel sock is there to protect the LP from sucking up a large particle and clogging it up or breaking it. The LP needs a pre filter.
Some remove the sock in the tank and use a Low Restriction 150 micron fuel filter between the tank and LP. Much easier to change than dropping the tank.
Do not use a regular fuel filter they are too fine and restrictive. The LP does not have much suction and cant pull enough fuel thru too fine of a filter.
As for cleaning the tank and keeping the tank clean look into Power Service Clear Diesel and or Bio Kleen
Also with every fill up you should be using a good fuel additive. Our trucks were never designed for todays Low Sulfur fuel. You need a good additive like PS Diesel Kleen or other good brand. To keep the injectors and LP lubed properly and the fuel system clean.

57diesel · 2025-10-05T16:15:18-0400

A consideration of what you put before the pump (and after) is the climate you will be operating in. Things are quite different if you rarely or never freeze vs those of us that need to run when its well below freezing for extended periods of time.

Oborowatibinast · 2025-10-05T17:47:50-0400

This is my first diesel so im trying to learn the ins and outs of fuel and oil treatment and how to get the most life out of em, for reference im in Texas, our winters probably average ~50° Fahrenheit with a occasional freeze once a year where ive seen a record of -12°, but for the most part, it's hotter than it is cold

94 6.5 diesel running and falling on face

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