LB7 fuel pump?
 

Need some help guys. Not real knowledgeable about these motors. Been driving this truck for 13 years but other than injectors I've never had a problem with the motor before. Last year I changed out the stock fuel filter for a 3 micron Donaldson (Nicktane adapter). My injectors were only going about 80k miles a set and i'm hoping to extend that with the Donaldson.

Anyway, the Donaldson filter is a bit larger than the stock filters I had been using since the truck was new. Since i installed the new filter and adapter for it, I've been having an issue with fuel. If I tow, especially heavy and long distance, when I shut it down it will restart then die and I have to pump the primer pump to get it to restart. I'm almost certain that I don't have an air leak... so what could be doing this? The truck has 330,000 miles on it now and I've never changed the CP3 or anything else on the motor other than injectors. No chips now and never had one. As I said, I know very little about this motor since I haven't had to screw with it. From my understanding, there is a fuel pump in the CP3. Is this so? Is this the only fuel pump or is there one in the tank? It also seems like I'm down on power a bit over the years. Thinking I'm starving for fuel, especially when towing. After 330k miles and roughly 22,000 gallons of diesel, seems like any pump(s) might have some wear.

The only other thing I can think of is that the slightly larger Donaldson filter is closer to the exhaust manifold and is causing vapor lock??? Either that or the pump just can't keep the larger filter full in hi-fuel-demand situations.

Anyway, I need some help from someone more knowledgeable than me. What do you guys think? Should I change the CP3? Can I add another pump if the CP3 is the only one? I've been considering changing out the factory fuel tank for one of the aftermarket ~50 gallon ones. Is there a pump in the tank like gas motors have? I could change that at the same time...

Note: After towing and shutting down, the motor restarts but only runs for 30 seconds or so. When I pump the primer, I do not have to crack the bleeder open. After that, truck restarts fine and runs till next stop.

You need to rebuild your filter head. The kit costs approx $20.

Other than the CP3 pump itself, there is no other fiel pump on any model Duramax. That said, you could install a lift pump which would also cure your issue with having to prime the filter head every time the truck sits for awhile.

I rebuilt the filter head when I changed filter sizes. Got the rebuild kit from Nicktane too.

As far as "after sitting a while", doesn't need to sit to do this. Turn it off after towing down the hiway and you will be pumping the primer regardless of if it sits for 2 minutes or 2 days.

Lift pump sounds like a good answer though. What's available / best setup for that?

Do you think that the CP3 should be replaced with 13 years and 330,000 miles?

cp3 may need to be replaced, that's a lot of miles. There's a return rate "bottle test" that you can search for, that test will confirm if you have issues.

For lift pumps, you have many options. I think Kennedy diesel is one of the best and easiest options, but there's also Fass and AirDog lift pumps available from many vendors.

Also, it sounds like you may have an air leak somewhere, replace the fuel hoses coming to and going from the filter head to start with. For $20 you may want to rebuild your filter head again, sometimes a small leak can cause big issues.

mine has a cheap inline pump and I added the cat pre filter. No need for the expensive stuff.


No there is no pump in the tank. The cp3 vacumms the fuel from the tank. Add a pump and a pre filter. The best thing about the cat filter is the cost. Only 17 dollars each. The factory filter should be good for 50K with the pre filter. And the cat is a 2 micron made in usa.

Thanks guys. I ordered the Kennedy single pump kit today. Also ordered another O-ring kit for the filter head from Nicktane. I'll also replace the supply side fuel lines. On Fire, the Donaldson filter I'm using is 3 micron and costs about $18 too. For now, I'll just continue to use it and hopefully not have to add another filter to screw with.

Hopefully this will fix my problem!! I priced a replacement, 2015 playing around on the Chevy website this weekend. Basically same truck I have but add 4x4 and leather. $61,000!!!!!!!!!!!!!!!!! Holy crap! I paid $38k for the one I'm driving brand new back in 2002. That's one heck of a price jump in 13 years. We're definitely going to hit 400k miles on this one unless something drastic happens and I have to replace it sooner. I towed ~9,000 lbs about 900 miles with it last week. Other than having to pump the primer pump every time I killed the motor, it did great.

Try replacing the hose coming out of the filter with a clear one. That way you can see if there is air getting in. One of the easiest things to do to rule it out

Belated update: The lift pump absolutely solved the problem. Apparently, the CP3 pump doesn't have enough balls to suck adequate amounts of fuel through a 3 micron filter. The lift pump keeps the filter full, even when towing 10,000+ lbs. Now at 347,000 miles and running great. Thanks guys!

what kind of lift pump did you use?
 

what kind of lift pump did you end up using?