Making no assumptions here, as working on diesels is not my day job:
I'm at 100,000 miles on my factory original stock 2015.5 GMC Denali HD.
After installing a lift pump which puts out 95 GPH at 11 PSI (indicated by analog gauge mounted on the pump output to engine ), I had a leak the morning after install when I used remote start. in that ten minutes, the truck dripped a basketball- sized puddle under it.
I found the leak and tracked it back to the primer/ plunger at the fuel filter head.
The leak had all but stopped on its own when the new oring seal kit for the filter head arrived.
When I removed and disassembled the fuel filter head, I found a decent amount of dried, crusty DEF crystals all over and inside the plunger assembly- under the triangular plate and on and around the orings in the plunger. Flakes between the metal plunger and the plastic with two o-rings found as well.
Apparently, the liquid DEF burping back out of the tank and sloshing everywhere was seeping into the filter head and drying to form small flakes. These allowed the fuel to leak past and then basically stopped leaking.
I cleaned the crap out of everywhere, replaced and lubricated the o- rings. And now, no leaks.
So- here is what I want to float out there:
If it was leaking at that pressure with DEF flakes in it- Does that mean that it was sucking air before that?
Its likely there was some getting in, air is much less dense so it would be easier to pull air through the leak than to pull fuel up from the tank. Did the truck ever randomly stall on you before, or ever fail to start without a LOT of cranking? i had the exact same problem on my 15.5, though i just replaced the whole head for 40 bucks more with a filter on it instead of doing the rebuild so i dont know if it was DEF related or not.
How many of us who have these trucks are driving around with $CP4 drawing air into the fuel at the filter head and don't know it?
I did not dyno or drag race the truck to prove it, but i felt a performance improvement after installing the lift pump. Is this why?
probably, i felt, and heard in the sound of the engine running a significant difference after i fixed the leak in my filter head.
If it is, then I would suggest a lift pump be installed on all Duramaxes - stock or otherwise. This alone might reduce the number of $CP4 failures.
to be fair, the new trucks do have lift pumps from the factory. while i agree they should all have lift pumps stock, the real issue here is the lousy location of the filter head.
I've also put a plastic bag around the filter head to keep it clean from now on.
Just my random thoughts.
i bought this. THIS should have come from the factory..... GMC & CHEVY Duramax Fuel Filter Relocation Kit - Western Diesel
So are you saying that delivering fuel to the pump under moderate pressure will have an adverse effect on longevity? If so, please elaborate. This was not my concern. My focus was on the possibility of the CP4 under normal conditions pulling somewhere between 5 and 10" of vacuum and drawing air past the parts where it leaked after the lift pump install.
the pressure at the inlet of the pump should be almost nothing, high pressure loads the input of the pump and increase the wear due to higher loads on the gear faces. the lift pump should be dialed back so the pressure at the CP4 inlet is only a pound or two. You want to push the fuel to the pump, not pressurize the inlet of the pump. Think of it more like relocating the CP4 inside the tank rather than adding a fuel pump.
So how much pressure head should a lift pump deliver at the CP4 inlet, and how did you determine this value?
I have to say, i agree with him, maybe not to the doom and gloom extent it was put, but i would not be running anything over 5 PSI at the CP4 inlet. There is just no need, the pump puts out so much more fuel than the CP4 would ever pull in that your never going to drain the fuel line even at 0-1 PSI. Running higher is just going to increase loads inside the pump.
The lift pump just needs to provide flow, and remove the vacuum load on the pump, nothing more. Will running it at 11 blow your truck up? probably not. But unless your making SilverGorilla levels of power, i also dont think its helping any. So if there is no gain, and a risk of failure, seems like an easy solution would be to dial the pressure down a bit.
If you have a twin / triplet monster that you sled pull or race with, you may be the exception to the rule.