Chevy and GMC Duramax Diesel Forum banner

61 - 73 of 73 Posts

LHN...We ARE the Joneses
Joined
26,485 Posts
I was merely trying to explain that looking to see what your pressure is at idle does not give a good account of how restricted your fuel filters are.
Pulling the power feed on the LP, and then measuring vacuum at the stock filter head at idle, IS a usable indicator of filter restriction. (2"Hg [fresh] vs 4-5" [end of life] )
Whereas added pressure could mask a restriction at idle.

I guess I will never understand why GM decided to suck the fuel from the tank to the CP3. Especially with the rail pressures the injection runs at. They finally wised up on the new L5Ps. Sucking fuel from the tank thru the fuel filter (especially a clogged filter) to the CP3 is just dumb. I work on many jet aircraft fuel and hyd systems. You always supply a main delivery pump with head pressure. Dean
Not really. With the easy $$ made over the years on fuel filter changes, I doubt that's what they were going for in the change up.

They switched from Bosch to Denso to overcome the CP4 failures.
Bonus, that system utilizes a FWS filter/pump at the tank, with added ease in filter changes and positive pressure forward.

Also, comparing fuel draw pressure vs rail pressure....it's all about fuel volume, not pressure on the inlet. Not much of a comparison between 6psi on one side vs 26-30k on the rail.
Supply volume is key.
 

Registered
Joined
130 Posts
Connecting to the Edge is not as easy as just connecting it.
You need the Edge EAS expandable probe, maybe you already have this 'dunno;.
Pressure sensor and a Universal Expandable starter Kit.

Here鈥檚 the kit you鈥檒l need to add a fuel psi to your Edge, if you buy seperate it鈥檒l cost more.
https://edgeproducts.com/shop/eas-competition-kit

I have the non expandable probe, actually I have 2 spare edge probes which means I鈥檇 have to buy this kit.
Under $300 for 2 gauges 2 pressure sensors all the wiring leaving my probe which sounded smarter for me and leaving my selections of pids on my CTS2.

On my LP, the sensor for my 5psi Amber warning light is connect to my LP.
The sensor for my LP to my gauge is T into the feed line to the engine.

The way I鈥檓 monitoring my gauges for when it鈥檚 time to change my filters explained buy several people/companies I trust, works for me.
I do have the expandable setup from edge. I'll look more into the cost, I'm planning on upgrading to the CTS2 since my CTS has been having issues. It will be a bit but hopefully I'll get everything wired up in a few months when I'm back with the truck. Thank you for the information, I needed it.

Sent from my SM-G965U using Tapatalk
 

Registered
Joined
2,604 Posts
Pulling the power feed on the LP, and then measuring vacuum at the stock filter head at idle, IS a usable indicator of filter restriction. (2"Hg [fresh] vs 4-5" [end of life] )
Whereas added pressure could mask a restriction at idle.


Exactly right. Every engine service I pop my Kennedy gauge on, and powerbrake it as hard as I dare with the lift pump shut off. If the restriction does'nt go below 5", I pop the fuse back in for the lift pump, watch the gauge run back up to 4psi of pressure, remove the gauge and slam the hood shut until the next service.

You dont need a dash full of gauges to monitor fuel filters...... its ridiculous.
 

LHN...We ARE the Joneses
Joined
26,485 Posts
Perhaps....
But for the overachiever, DRC has covered every angle on it.
 

Registered
Joined
7,275 Posts
Pulling the power feed on the LP, and then measuring vacuum at the stock filter head at idle, IS a usable indicator of filter restriction. (2"Hg [fresh] vs 4-5" [end of life] )
Whereas added pressure could mask a restriction at idle.
I have the Kennedy psi/vac gauge that snaps on the test port where I can check both psi and vac if I feel the need to.
Switch off my AD to check vac, turn it back on to check psi.
The numbers you stated is what Kennedy told me to look for when checking.
 

Registered
Joined
7,275 Posts
Perhaps....
But for the overachiever, DRC has covered every angle on it.
Yep, when your retired there鈥檚 so many things to think about doing to kill time and ignore the wiff and get away from the constant QVC chatting.
 

Registered
Joined
380 Posts
Pulling the power feed on the LP, and then measuring vacuum at the stock filter head at idle, IS a usable indicator of filter restriction. (2"Hg [fresh] vs 4-5" [end of life] )
Whereas added pressure could mask a restriction at idle.
Not really. With the easy $$ made over the years on fuel filter changes, I doubt that's what they were going for in the change up.

They switched from Bosch to Denso to overcome the CP4 failures.
Bonus, that system utilizes a FWS filter/pump at the tank, with added ease in filter changes and positive pressure forward.

Also, comparing fuel draw pressure vs rail pressure....it's all about fuel volume, not pressure on the inlet. Not much of a comparison between 6psi on one side vs 26-30k on the rail.
Supply volume is key.
You are making my point for me. If you read my post what I am trying to get out is about flow. Any fluid system, whether it be hyd or fuel will run more reliably when there is some head pressure on the pump. You don't need much but it does need to be (and stay) positive. This reduces the chance of cavitation and induction of air in the system. This also will increase the life of that pump. Of course too much head pressure can be detrimental also but maintaining a small amount of positive head pressure will ensure the system receives all the fluid it needs. When you look at all the fuel related isssues the Duramax has had over the years prior to the L5P release it is easy to say that it is better to push the fuel than to suck the fuel. Dean
 

Registered
Joined
7,275 Posts
Maybe don鈥檛 start off by saying gauges are not worthy for a easy way observing filter life.
Dragging out something that most don鈥檛 care about, just keep it simple something like the dic ave mpg lie-o-meter, oil life.
 

LHN...We ARE the Joneses
Joined
26,485 Posts
When you look at all the fuel related isssues....
But you're not considering that the CP3 is designed to pull the fuel efficiently.

Correct. Positive pressure can be a solution...nowadays.

The problem with the fuel related issues that seem common on the Dmax, is not so much the vacuum draw, although it is a contributing factor.

We never had a problem (sucking air) with the design until we were forced to run ULSD vs LSD that the system (and the CP3) was designed for.

The lower sulfur formula doesn't play well with rubber components. As a result, they decay quicker and seals fail. Aeration of the supplied fuel is a result.

My comment/debate was in response to your criticism of GM not getting it right in the beginning. Which they did. It was the EPA's mandate that caused the problems later on, many years after the design was implemented.
 

Premium Member
Joined
4,643 Posts
I guess I will never understand why GM decided to suck the fuel from the tank to the CP3. Especially with the rail pressures the injection runs at.
Let me help you with that issue. One of the greatest enemies of a diesel engine (unlike the turbine engines you work on) as far as fuel is concerned is water, emulsified or free, with free water being more easily and efficiently separated from the fuel.

GM's stock fuel filter sits between the tank and the CP3 with the first side sucking the fuel from the tank, much like an inline fuel pump outside the tank. It is a combination Fuel Filter and Water Separator. The water separation works best in suction, before the water gets emulsified in the pump mechanism.

This same principal is used in the Lift Pumps so many add to their system which incorporate a WS and a FF. The WS is prior to the pump and the FF is after, making for the most efficient removal of water possible with today's technology.

And remember, as Hook said, this technology was developed long before the advent of the ULSD that was foist on the nation by the EPA, with little regard for the consequences to us, the owners of diesel vehicles.
 

Registered
Joined
380 Posts
But you're not considering that the CP3 is designed to pull the fuel efficiently.

Correct. Positive pressure can be a solution...nowadays.

The problem with the fuel related issues that seem common on the Dmax, is not so much the vacuum draw, although it is a contributing factor.

We never had a problem (sucking air) with the design until we were forced to run ULSD vs LSD that the system (and the CP3) was designed for.

The lower sulfur formula doesn't play well with rubber components. As a result, they decay quicker and seals fail. Aeration of the supplied fuel is a result.

My comment/debate was in response to your criticism of GM not getting it right in the beginning. Which they did. It was the EPA's mandate that caused the problems later on, many years after the design was implemented.
I will completely agree that the design works and the CP3 was designed to pull fuel from the tank. Also there is merit to drawing the fuel into the water separator. My knowledge on the Ford and Dodge systems is very weak but I believe they both used pumps in the tank to push the engine (at least on the direct injection versions). My Duramax is an 08 LMM. I purchased it used in 09 with only 7k on the odometer. (Who gets rid of a truck like that with those miles on it is a whole other story). I never had any fuel related issues with the truck when I purchased it or ran it for the first few years. When the truck had about 50K on it I decided to add the lift pump. With my years of experience on aircraft fluid systems I saw the effects of running pumps at a vacuum draw and what aerated fluid can have on high pressure fluid systems. I plan on owning this truck for quite some time. I immediately saw a difference in the smoothness of the idle and the response of the engine during acceleration. The EPA mandated the use of ultra low sulfer diesel fuel in the model year 2007. GM did little to address the use of the ultra low sulfur fuels till the L5P came out. Simply put the system works better and will last longer with head pressure on the engine pump. You can design a system to run sucking the fuel from the tank but why. The merits of a pressurized system to me simply outweigh it. The specific weight differences between diesel and water are high enough that a water separator should still have little issues removing the water especially if the separator is designed with a swirling effect to help pull the water out of the fuel.

Please, don't take this as being combative or arguing for the sake of arguing. I just look at this from another prospective because of my background. To me that is what this forum is all about. Dean
 

Registered
Joined
7,275 Posts
Now back to lift pump filtering, liftpumps with filters one of the better ideas from the companies that offer them, and should be thanking GM all the way to the bank.

On psi knowing when it鈥檚 time to change the filters is a no brainer.
Add a psi gauge to your liftpump along with new filters good for having a baseline with psi.
If the LP is putting out, for example 8 psi when idling, when you accelerate the psi will drop maybe .5 - 1 at the most then recover quickly.

Fast forward to now you have 15k-20k on those LP filters the psi idling will be lower than 8, when you accelerate it鈥檒l drop much more than 1 psi and will NOT recover as quickly if it will even recover.

Pretty simple way to know when it鈥檚 time to change filters, much more accurate than the oil life % that people live for.

PSI off the engine works a little different as you have a large drop with psi when accelerating even with a clean filter.
That one it鈥檚 better to go by when idling.
 
  • Like
Reactions: Dean E

Registered
Joined
7,275 Posts
Pulling the power feed on the LP, and then measuring vacuum at the stock filter head at idle, IS a usable indicator of filter restriction. (2"Hg [fresh] vs 4-5" [end of life] )
Whereas added pressure could mask a restriction at idle.
For the ones that don鈥檛 quite understand vacuum vs psi readings.
The Kennedys standard test port gauge has a max 7.5psi.

If you need/want the larger psi option which I have, check with Kennedy to order that one, or you might get the 7.5 psi.
Kennedy Diesel

IMO having a diesel, this test port gauge or something similar, is something everyone should have in their toolbox.
If anything you鈥檒l know when you should change your filter, not thinking it鈥檚 about time to change it.

With my liftpump off I got about 3 vac, with liftpump on it looks like just a little above about 7.5, my gauge in the cab reading off the fuel filter head was just a hair below 8 all while idling, close enough for this RedNeck.

I wanted to check both because lately with the colder weather that we鈥檝e had 30* 40* the psi off the engine jumps up to about 12 then back down.
Today when I checked vac/psi it was 58* and operated normal.
 

Attachments

61 - 73 of 73 Posts
Top