rbox

I have mounted the Cat 2 micron filter setup similar to what gacamper did. Pictures to follow. My fuel pressure is running about 8 idle but at this time I don't have a way to check it while driving. I have 2 questions...

1. If I am running 8psi at idle post-filter, will it pull down to 0 at WOT or am I good?

2. I am using the cheap Mr. Gasket fuel pressure gauge (#1561, the same one geno's sells). Is it safe to keep this installed on the filter mount long term? Is there any danger of it coming apart and leaking?

Thanks!

TonyB

It all depends on which fuel pump you are running.

Stock...it may pull down.

Aftermarket, not likely.

Tony

rbox

Running the Cummins replacement in-tank pump. It was retrofitted at the dealership when the injectors were replaced.

rbox

I understand that the Duramax uses the CP3 with no lift pump at all. So the CP3 sucks fuel all the way from tank. Why then would it be so important to supply the CP3 on the Cummins with more pressure on input? Isn't it designed to suck fuel, unlike the old VP44?

It looks like all I need to do is add an in-cab guage so that I can monitor the condition of the fuel filters and I'll be good. Am I wrong?

mini14

at the very least u should be adding a needle valve before the guage incase of a leak, and as a pressure snubber. imho those things r inaccurate junk, get yourself a nice liquid filled one from northern hydraulic or www.surpluscenter.com .

Ace

You will probably see different numbers when you get a good gauge on it. Mine runs 10psi idle, 9psi just about any other time well into the throttle, and holds a steady 7psi at WOT making 30lbs boost.

bradler

with 2 mic filter on stock truck i also see 9psi idle, 5psi normal driving, but i can see 0-1psi wot...

bradler

also just remembered a disscussion on here about dodge procedure for testing the lift pump, and actually as long as the flow volume is above a specified amount the psi doesn't matter. i know the aftermarket pump makers like to say you need 15psi at cp3, but as long as the volume supplied is sufficient then cp3 still has enough fuel to lubricate/cool itself so i'm not worried about 0 psi at wot myself....

BLACK PEARL

If you see 0 PSI at WOT and your truck make a loud sneeze that is a miss. Then you will wish your truck had some pressure at the CP3. But to each their own.

rbox

I am getting conflicting opinions regarding the pressure the CP3 needs to operate. On the Duramaxes, it pulls a vacuum and sucks fuel from the tank, and GM does not seem to be having an epidemic of CP3's failing. However there is no lift pump there to die and impede the flow of fuel.

Why then do I hear from some that the CP3 needs pressure on input?

I understand that the VP44 needed pressure on input, I went through a lift pump failure with one. But possibly that idea is incorrectly carrying over to the 3rd gen with the CP3? Possibly by some aftermarket fuel pump manufacturers looking to cash in on the 3rd gens just like the 2nd gens with the VP44's?

I understand the need to flood the CP3 with fuel in modified applications with higher HP injectors, etc.

Maybe in stock form, the lift pump is actually the problem on our trucks? When it fails does it impede the flow of fuel and actually make it harder for the CP3 to suck fuel from the tank?

Does the Dodge lift pump allow more fuel to be pulled through it by the CP3 if it is not pumping enough to supply the CP3 at WOT?

If not then I would say that the Dodge lift pump is hurting more than it is helping even while it's functioning as intended.

Does anyone actually have the specs for the CP3? Has anyone talked to someone at Bosch regarding the CP3's requirements?

Ace

It depends on the lift pump. The '04 and up in-tank pump is a flow-through design. The earlier pumps are not, so a LP failure would starve the CP3.

I have also heard conflicting reports on whether or not the later trucks equipped with the in-tank pump will actually run at all with a dead LP. Still waiting for a definitive answer on that. May have to just unplug the thing one of these days and see for myself.

trik396

Thing is, though the Duramax and Cummins use SIMILAR CP3's they are NOT the same. There are different requirements for flow between the two. Can our cp3 pull fuel... absolutely... can it pull through a dirty fuel filter? Don't know. The differences have to do with fuel cooling the injectors, from what I remember. There was something else but my memory is not what it used to be.

rbox

All of this shouldn't affect the injectors though, correct? Because they are on the high pressure side, and as long as the CP3 can build pressure and supply the rail to the prescribed specs, the injectors wouldn't know the difference right?

I am no expert on the CP3 but I would think as long as it can get enough fuel in to fill the plungers to capacity it shouldn't care if it has 50psi or 5psi on input. Am I wrong?

rbox

And as far as pulling through a dirty filter, I wouldn't want that anyway. Our lift pump couldn't even push through a very dirty filter. I agree that pressure must be monitored.

turbohi

ok...so this is my take...on the LP. my question would be....has somebody put a pressure guage on the high pressure side and montitured both sides??? so if the 0psi on the input has anything to do with the psi on the high side???? i dont know maybe this doesnt make sense..but it would be somehting i would try...??????