Please excuse what may be a few stupid questions, but I'm interested in the fuel filtering system.

From what I understand, the Duramax uses a CP-3 injection pump like the 3rd gen CTDs, but the Duramax does not have a lift pump. Does the CP-3 used on the Duramax have an auxilary integral pump to draw fuel from the tank? If not, I would think the fuel filter on the Duramax would run under a slight vacuum. Is this correct, and how can the GM guys run the stock filter and another filter in series? There are several kits for Duramax; one uses a 660 series Racor , another one uses a Baldwin and one kit even uses a 1R749 Cat filter.

 

May be they are using an in tank pump like the 05 Dodge does now. Seems I read a post on the 2nd gen site that talked about the GM and Ford using in tank pumps and not having the fuel pump issues as the 2nd and early 3rds are having..

 

The only thing that makes me think they do not have pump in the tanks is that the stock filter has a manual pump to fill the filter, but I'm not sure.

Any Duramax experts here?

 

I've been told my a person who realy knows Duramaxs that they don't have a lift pump and even the stock filter runs under a vacuum.

Has anyone here added an additional filter upstream of the lift pump? If installed properly it shouldn't be too difficult to prime and some filters have a manual pump (Racor and Stanadyne) to aid priming.

 

Confirmed. Dmax and CTD both liscense the common rail fuel system from Bosch that uses the CP3 high pressure pump. CTD uses lift pump for quicker starts (especially in the cold) and easier servicing of filters (manual primers?).

 

I've allways heard the VP44 could fail prematurely if the inlet pressure had anything less than a positive pressure; I guess the CP3 is not as sensitive. Is this correct?

Do you think the '04 lift pump could handle an additional drop of 0.5psi in inlet pressure due to a extra filter?

 

That is correct amigos. CP3 will suck from the tank if lines are clean?Work truck 04 duramaxpad duelly flat deck in to dealer for plugged fuel sender ( in tank ) 1: and failed CP3 injector pump 2: Three months apart on a new truck? There is no lift pump on a gmc. Don't feel to smug, your dodge polycarbonate plastic tank has several tiny screened inlets/outlets?

 

Was your screen plugged in the tank?

 

Both pumps are lubricated by the fuel so if you starve a cp3 or a vp44 of fuel, you can/will damage the pump.

That's why a low pressure fuel gauge (0-15psi) is the first thing you should buy for your truck. If the pressure falls below 4-5psi, you are starving the pump.

I think it would handle a .5psi drop, but I think the filter that is there is more than is needed. Your extra filter is still not going to save you if you get bad fuel. You'll just have to change 2 filters instead of one.

 

I have an AirDog so if the fuel pressure were to drop below 7psi then the light would come on in the cab. Has anyone had their ECM replaced???

 

So, is low fuel line pressure the main cause of injector pump failure? Mine failed at 14000 miles. Warranted but no good reason given by dealer.

 

This is wierd, so the CP3 will draw fuel. I have had a LP failure and the truck still ran (FP guage showed vacume), however I read on here that the trucks died w/o the LP. Is this just because the CP3 wouldn't suck through the dead LP? Was mine just an anomaly?

 

Both the Duramax and Cummins have low pressure lift pumps within the CP3.

The Duramax uses no inline or electric lift pump but the GM engineers designed a high flow/low vacumn fuel system which includes 1/2" fuel lines, larger banjo bolts and hiflow tank module. This allows the CP3 to draw fuel under reasonable vacumn until GM put a better (lower micron) filter in the system to prevent injector wear. Even so the early and later Duramax run out of fuel when horsepower is enhanced and also give trouble in extreme cold.

The Dodge fuel lines/fuel system is small, low flow hence high vacumn but is boosted by the mighty (plastic) lift pump attached to the fuel filter. If (when) the lift pump fails it can (and ususally will) fully restrict the fuel flow depending what clock position the lift pump failed. The AirDog uses hi flow 1/2" fuel lines, fittings,hi flow filters and has internal check valves in the pump that are engineered to bypass and allow the CP3 to draw fuel from the tank even without the AirDog running.

The 2003 Dodge manual shows minimum fuel pressure as 11 or 11.5psi (memory?) and the 2004 manual is silent on pressure but gives a flow test per time. Most of the pumps I've checked are below the 2003 psi spec's at idle...........and keep going down with acceleration.
With high horsepower trucks and stock lift pumps the CTD can pull a vacumn or negative psi if the stock lift pump is still running. Performance drop at higher rpm is noticable to anyone familar with this.

HTH's, Larry

 

with the third gen Cummins , all that is required is that the inlet restriction at the inlet of the lift pump not more than 6 in\hg. at full power load output, any filter added before that lift pump should not have a micron rating less then 25 micron , basically it should only be a rock catcher. The output press. on that lift pump with the CP3 should be a positive press., if the lift pump does fail , rarely do we have one that won't run and usually the complaint is low power. biggest problem they are having with the lift pump is the lubricity of the fuel, especially the winter fuel , and the negative brush wear out which Airtex is trying to fix now.

 

Roger Rodbolt:

Does the small fuel line at the tank cause any problems for the Airdog, considering that the Airdog flow rate of 80 GPH is double that of the stock pump?

What type pump does the Airdog use; a vane, gerotor or something else? Does the Airdog use the same motor and/or pump as the model 135A?