OK lets start out by saying I am not a diesel racer, or elbow deep in diesel fuel everyday... I have always tinkered with cars, trucks, and have a decent knowledge of mechanics (old high school hot rodder, 1/4 mile track racer when younger) grew up with dad as a very well known local mechanic all his life...

With that said lets talk lift pumps (or fuel supply to the CP3 in general)....

It seems like the general concenses on this board is that any HP mod will benefit (or needs) a lift pump upgrade from the factory unit. In fact some would argue that these trucks need a upgraded LP before they roll off the lots...

Orginally I was led to believe that if a LP failed it would leave you on the side of the road because the CP3 was not supplied with fuel. Appearently that is true and not true... Now I am being told that only the trucks 305/555 models with the LP mounted on the fuel canister is the ones that will leave you stranded because those LP's block the fuel line when they fail; but the in-tank set-ups will allow flow...

Then I was led to believe that the CP3 would not work (or gets damaged) if it wasn't "fed" fuel. Now I been told this is not the story either, that is can "suck" fuel if it has a free flowing supply line. Someone recently said that the FCA signal changes at low FP levels.

So with all this being said, what are the facts??? (all questions referring to the input side of the CP3)...

1) When is a aftermarket LP needed???
2) At what PSI (low) does the FP start to effect the performance of the CP3???
3) At what PSI is the FCA signal altered???
4) Will more PSI increase the flow of a CP3???
5) What is the max PSI a CP3 can handle???


I am not looking so much for opinions (from the guys that are justifying thier LP purchases) here as much as I am looking for answers leaning closer to facts from the diesel junkies/guys that "know" and live these trucks... Not trying to offend anyone with the comment, I just think that their is alot of guys like me that want to know that they are spending thier money on stuff they need, not just because it is the latest and greatest thing being advertised...

ALL RIGHT GUYS SPILL YOUR GUTS, LET'S HEAR IT?????

 

I am wondering the same things. Also I am wondering what is the best lp to replace the stock one with that doesn't cost alot?

 

It would also be nice to hear what role the entrained air in the system REALLY plays as the two leading manafactures of the aftermarket pumps suggest. Is there any proof that it hurts as much as whats suggested by the manafactures or is it really just a smooth marketing ploy? I believe its there but to what extent does it really affect us? Some of the higher end units offer no such feature, they just supply a ton of fuel yet they are on the majority of the top contenders trucks. I have only personally owned one stand alone air removal system and never noticed it to do anything that my stacked carters didn't do. It was many years ago but I still lost two VPs with the magical system.

 

Wonder how many festerig wounds THIS will open again.


The real answer to all your questions is "it depends".


Then I was led to believe that the CP3 would not work (or gets damaged) if it wasn't "fed" fuel. Now I been told this is not the story either, that is can "suck" fuel if it has a free flowing supply line.

The CP3 low pressure pump will suck fuel to a certain degree. Like anything else that is relying on suction line size, distance, and height will impact how much. Will it suck enough to supply factory fueling on a Dodge truck? Nope, not with the stock configuration. Will the truck run? Sure, its just a question of how long, and, that depends on a lot of different factors.


1) When is a aftermarket LP needed???

It depends, on demanded HP, mods, driving style, etc.


2) At what PSI (low) does the FP start to effect the performance of the CP3???

It depends on the answer to #1. As a very general rule is once the supply pressure drops under 4 psi the potential for damage exists. How often the pressure is under that will drive the need for more supply side fuel.

3) At what PSI is the FCA signal altered???

No evidence it does. The FCA is run by the ECU and the ECU will keep demanding pressure required to meet the demand irregardless of supply pressure. This is demontrate by dropping rail pressure, popping in the exhaust, and high EGT's when the fuel system can't keep up.


4) Will more PSI increase the flow of a CP3???

Sure, to the point it is supplying enough fuel for the demanded pressure. Beyond that there is some evidence that ramping the fuel pressure relatively high will reduce cavitation in the low pressure side pump which translates to better rail fuel quality and better injection events. It depends on the criteria one is using to determne efficacy.

5) What is the max PSI a CP3 can handle???

Where in the CP3? The high pressure side should be good to around 29k psi but that is pushing its design limits. The low pressure supply pump will generate 180 psi to feed the high pressure circuit under full demand. Some are running 100 psi feeding the supply to the gear pump with no side effects. The answer again is, it depends.


Entrained air gets debated over and over. Does it effect anything? What does it effect? How much effect does it have? The answer is invariably "it depends". Does it even matter when you are pushing enough fuel to throw a 20 ft smoke column? I would guess not. Does it matter when you are looking to eke the last HP out of the injected fuel and maximize efficiency? Pretty good arguments it does contribute.

A lot of things are relative to what each person is trying to accomplish and what they use for criteria. About the only thing everybody agrees on is lack of fuel pressure will eventually kill the IP. As I said, the answer "depends" on a lot of other variables.


So many questions and so many opinions, and, we haven't even got to the impact of fuel quality and fuel temperature.

 

Well I am told that Duramax's don't run lift pumps, but thier CP3 are basically the same as ours, just different mounting. Look at this post and see where some of my confusion is stemming from... https://www.dieseltruckresource.com/...d.php?t=227406

The whole air thing is another thing that would be good to add to this thread, but like you said is more speculation then proof... I would guess a cavation issue at high pressure could cause injector damage (I have seen the damage it can do to a boat prop) but who knows...

Come on you LP suppliers and big dogs, jump off the porch and school us.. Answer some of the questions and help us decide that we are spending good money on a fuel system and it's needed...

 

Thinking about the temp thing the warmer temps should help release the air, no? I believe lower filtering (2-3 micron) to be a good thing and possibly second in importance to supply but there is no proof to my beliefs, just my arm chair engineering at work LOL

 

Some DMAX guys are pushing 500hp on stock trucks with an exhaust... I believe the CP3 will pull up to 20 in/hg.

On my truck I want to pull the in-tank pump for a frame mounted so that I can bypass it if I am back in the woods and the LP fails (I know the in-tank is designed to bypass, but I'd rather have an actual bypass)

 

I dont know if it's fair to compare the d-max pump to the cummins???
the dmax pumps get noisy when you put high lp PSI to them and dodges do not...to me it's sounds like the dmax and the cummins pumps are very slightly different..I cant confirm it?..maybe John from floor it or Shane frome wicked will see and post the diffrences if any??
but to me this makes me think the dodge CP3 needs or should have a LP and the dmax can go without..but does benifit from some LP help..

 

Subscribed as i'm interested in real FACTS also.

 

I have always heard its just the mounting that differs.. but yes it would be nice for some facts.

 

so why do cummins pumps like lots of psi and the dmax pumps make noise with high LP psi??

 

The Dmax systems vary a lot from ours. They also run a fuel cooler mounted inside the frame rail that some guys mount fans on. Why do they require cooler fuel and ours do not?

I have this question about lift pumps. Why wouldnt you want the added benefit of higher fuel pressure to the CP3 and better filtration? There are just some things you cant cheap out on and this is one of them. Sure, lots of guys are running the stock LP and are doing fine. There are also guys running stock turbos to 50 SPI with nitrous on stock trannies. You are just running on borrowed time.

the LP is a supporting mod. It will only pick up the power that you are loosing from lack of fuel. It has been proven the CP3 needs fuel for cooling and lubrication. Running any performance modifications adds stress to the CP3 beyond what Cummins designed it for. Do your CP3 a favor and feed it some highly filtered adequately pressurized fuel.

Just ask John or Shane just how many "low mileage" CP3's they get to mod and they are already junk. Debris and low fuel pressure is what kills a CP3.

 

It has been awhile since I've been in one of "these" discussions...

There are differences in the "needs" of our Cummins as opposed to the Duramax. If I remember correctly our Cummins uses fuel to cool the injector where the Dura doesn't. I believe there is a difference in the cp3's related to that ability, ie, more fuel to cool the injectors.

There is a chance I've got this screwed up totally...

BTW- I'm one of the original Walbro GSL392 guys (still pumping at 40,000+miles)

thru 4 fuel filters nonetheless....

 

Great question, lets add that to the list!!!!


I have seen the effects of a tranny and turbo blown up and when mine takes a dump I will be upgrading but I know the money will be well spent because I have seen proof of it (but it is not a tranny or turbo thread), I have not seen proof that a aftermarket LP is any better then a factory one for the guy with stock/mild mods on his truck...

Because I don't know that an aftermarket set-up IS any more realible sure it might filter more and I am sure that is a good thing, but how many trucks are out there with 200k on them using the factory set up????

OK so at what PSI is it that this happens; 1psi-6psi where???? Just give me a number I know someone should know if they are pushing better pumps... If the CP3 can even pull fuel then isn't 1psi enough to say your keeping a positive side???

I am hoping that they jump on here that is why I titled the thread like I did so the "guys" could answer some of the questions above...

 

I think the point of Matego's post is to say if you are doing any mods that are going to increase power you need to look at the supporting mods also.Dodge has been notorious over the years to equip the trucks with just enough to supply the factory rated hp and don't leave much room for any substantial increase.Back when I started bombing my bone stock truck I started with a Tri-dog w/crazy larry.The truck ran great except on top end and then it just felt like it quit pulling.I added a Fass and the problem was resolved.So it really comes down to what you consider mild mods.If you had a conservative tuner and were only using it for better mileage and towing,I would not be looking into an aftermarket pump.

I can't speak on the fuel pressure the stock pump can maintain with x amount of power added.I already had a Fass when the fuel press gauge went on.But considering the tow and performance levels of the tri-dog ran great with no flat lining like crazy larry created,I would say the stocker can support a 70-100hp gain.I know this isn't the technical hard facts your looking for but its a start.Most people aren't paying much attention to this stuff till they are well into the modding process.