08 LMM 0%fuel filter life / Power derate
 

2008 GMC 3500. 4x4 Sierra. Had the truck a month now every time I hook up to the horse trailer the engine light comes on power derates and it goes to 0% fuel filter life. Has new AC fuel filter and replaced both hoses on filter housing hoses by tranny and on top all look good and not linked. not running any tunes stock exhaust for now. It has a air dog 200 with new filters as well but I have it bypassed and still the same problem. It will also go to 0% filter life at 80MPH when passing with the truck empty but it won't derate unless the trailer is on. After a cool down it will clear and go back to running and clear itself. Stealer ships in area are clueless. Local diesel shops want me to leave it with them. I can fix it just gotta learn these junky systems. I'm really hating this truck. Can't wait till I get my 96 dodge 12 valve fixed from being in a wreck. Any help would be greatly appricated.

the fuel life will drop to 0% if the fuel pressure drops too low or you reach 20k miles.

you are likely dealing with low fuel pressure.may be the fuel pressure sensor or pressure regulator. i would run the air dog as this will help keep any air out of the fuel if there is any leaks.

it may also be the pressure relief valve leaking. see here: http://www.kennedydiesel.com/docs/Sh...Test%20etc.htm

if that all checks out then i would guess it is a bad CP3

Like 2004LB7 said we need to verify what the supply pressure is off the lift pump, and make sure there is no leaks in the fuel system. If everything seems to check properly typically the culprit could be a weak CP3. We want to Verify supply pressure off the Air Dog first. to be sure.

I'm looking at ordering the shim kit for the rail relief plug. And put the air dog back in service and bypass the factory fuel filter and install a fuel pressure gauge.

I would not remove the factory filter unless you are putting another filter in its place. It works as a good backup for when you are changing the lift pump filters. If something was to make it passed the stock on can catch it. It also has the water removal function too

The lift pump pressure should make any restrictions of the extra (factory) filter in line a non factor

Ok. So far I've shimmed the rail relief valve .060 inches ( 3 shims ).
Hooked the air dog 2 back up. At 18 PSI.
Still doing the loss of power due to fuel filter life at 0%.
Is there a strainer screen before the pump mounted on the back of the CP3 ?

Ok. I pulled the bed pulled out the fuel sending unit from tank. Had no trash in it and all hoses and fittings are tight. Put all that back crap back on then pulled the filter head and replaced all the O-rings in it and put it back on. Test drove without the horse trailer and at WOT around 80 MPH it goes to 0% fuel filter life left and then derates power. If you shut down the truck for 5 minutes it will run with full power and after a bit the engine light will go off as well. Appricate all the help I can get.
__________________

Are you running any big tunes when this is happening?

What brand filter are you using?

Do you have any way to monitor fuel pressure while driving?

No tunes. All stock.
AC delco filter on engine and air dog filters on pump.
Has 15 PSI on filter head at all times thruout peoblem. Never looses fuel pressure from air dog
Ran a Manuel gauge with 12 foot of hose into cab for testing.

did you attach the gauge before or after the filter? you need to get a hold of a Tech 2, V2 or another tool that can monitor the high side fuel pressure.

it may be that it is as simple as a kinked hose leading up to the CP3 or as bad as a dead CP3. but because your truck seems to run fin otherwise i would think the CP3 is fine.

thoroughly inspect the lines leading up to the CP3 after where you attached the gauge.

the only other thing i can think of is a bad pressure sensor