CP3 ... CP4 ... Lift pump ... What's the difference?
1 - 10 of 10 Posts
Joined
·
18,021 Posts
Your LML Duramax will have the CP4 pump
LB7-LMM Duramax is equipped with the CP3 pump
I'm no expert. But there is an excellent YouTube video where a shop takes each apart and explains the difference. Basically whe a cp3 quits working it just quits without exploding. It's typically a slow decline.
The cp4 on the other hand doesn't have a pinned piston and if it rotates slightly it tends to explode and send tiny bits of metal all through your fuel system. That includes rail lines, injectors, return lines and finally your tank. Sometimes it just rotates enough out of alignment to send metal to the injectors and shuts down before it goes POW. I remember seeing a picture of one in two pieces after it went.
The cp4 on the other hand doesn't have a pinned piston and if it rotates slightly it tends to explode and send tiny bits of metal all through your fuel system. That includes rail lines, injectors, return lines and finally your tank. Sometimes it just rotates enough out of alignment to send metal to the injectors and shuts down before it goes POW. I remember seeing a picture of one in two pieces after it went.
With the potential catastrophic failure of the CP4 (the "successor" to the CP3?!?!) some have removed their CP4 and replaced it with the CP3. I don't know what all is involved, but there must be a number of DIY descriptions and maybe videos. Since I have an LLY with the CP3, I haven't studied the CP4 issue that closely.
GM thought it was an ok idea for the CP3/CP4 to suck diesel all the way from the tank, through the filter, and into the pump. Some have claimed that it's extra work for the CP3/CP4 pump that should be corrected by adding a lift pump, ideally near the fuel tank. For the older trucks, a common issue is for the line to develop a small leak and you lose prime. It's not fun if you have to prime it every time to get it started again. Without a lift pump, the fuel lines are under suction and tend to suck air in, and not fuel out, making it hard to find the leak. In most cases, a lift pump will prevent the problem (or, as some claim "cover up" the problem, but I'm ok with that).
GM thought it was an ok idea for the CP3/CP4 to suck diesel all the way from the tank, through the filter, and into the pump. Some have claimed that it's extra work for the CP3/CP4 pump that should be corrected by adding a lift pump, ideally near the fuel tank. For the older trucks, a common issue is for the line to develop a small leak and you lose prime. It's not fun if you have to prime it every time to get it started again. Without a lift pump, the fuel lines are under suction and tend to suck air in, and not fuel out, making it hard to find the leak. In most cases, a lift pump will prevent the problem (or, as some claim "cover up" the problem, but I'm ok with that).
Thanks all - I've learned a lot in the last couple of days about the CP4 problems on the LML. My diesel shop is the one who 1st brought this potential problem to my attention otherwise I would have been blind to it.
- I'll get a lift pump installed, once I save up the money. Until then, the shop said to use Stanadyne Performance during the warm months and Stanadyne Winter 1000 for the cold months (I live in NYS). Does this make sense?
- Is there a "plug and play" CP3 for the LML's? If yes, is it worth swapping or will a lift pump take care of the CP4 problem? I watched a couple video's on swapping them but they only show the mechanical side, not anything done to make it paly well with the system.
- I'll get a lift pump installed, once I save up the money. Until then, the shop said to use Stanadyne Performance during the warm months and Stanadyne Winter 1000 for the cold months (I live in NYS). Does this make sense?
- Is there a "plug and play" CP3 for the LML's? If yes, is it worth swapping or will a lift pump take care of the CP4 problem? I watched a couple video's on swapping them but they only show the mechanical side, not anything done to make it paly well with the system.
Joined
·
18,021 Posts
The CP3 Conversion is not necessary IMO.
As long as you install a lift pump, like a Kennedy Single, add extra fuel filtration, purchase your fuels from well-used stations like Truckstops ( T/A, Loves, Flying J , etc ) and use a fuel additive with Lubricity in each tank of fuel, your chances of a CP4 issue are greatly reduced
Joined
·
113 Posts
There are CP3 conversion kits for deleted & emissions intact. You stated your deleted but if your EGR is still in place it's a little but of a job doing the swap. Other than a little bit of plumbing changes it is a direct swap as far as bolting in place.
The lift pump will ease the strain on the CP4 but no guarantee it still won't grenade. The extra filtration on lift pump helps, & run some lubrication like Stanadyne & good fuel is the biggest help.
Joined
·
8 Posts
I watched that video Mikey52 posted some time ago, and that convinced me to do the conversion after I decided to keep my truck long-term.
A lift pump, good filtration, and additive use are all good things and will likely prolong a CP4’s life (as they would with any injection pump). But the CP4’s design issues - steep cam profiles and no restraints on piston rotation - were enough to make me uncomfortable with it. The CP3 is arguably superior.
A lift pump, good filtration, and additive use are all good things and will likely prolong a CP4’s life (as they would with any injection pump). But the CP4’s design issues - steep cam profiles and no restraints on piston rotation - were enough to make me uncomfortable with it. The CP3 is arguably superior.
1 - 10 of 10 Posts
Join the discussion
Join now to ask and comment!