LMM CP3 on LLY engine?

Sud

Sud

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May 15, 2012
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Lawrenceburg, KY
I'm fairly sure my fpr is shot... Actual fuel rail pressure is off from desired fuel rail pressure at idle, especially when the engine is cold.

Debating swapping to an LMM pump.

What is involved?
Is this a good/bad idea?
Is it worth it, for the increased rail pressure? or should i just stick with the LLY pump and replace the regulator?

I understand i would need to have the ECM re-tuned ("Idaho Rob" EFI tunes currently, would have him do the re-tune if i do this cp3 swap)

Did a search and found this thread, but not much info here...
http://www.duramaxdiesels.com/forum/showthread.php?t=4205
 
DBUSHLB7

DBUSHLB7

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Mar 9, 2012
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The LBZ/LMM cp3 would work great for you. Being able to hold rail pressure is key. The dealer where I purchase my cp3s at does not require a like for like core but I've heard some do. Find out before you buy. If you have a decent amount of miles on your truck I'm sure your CP3 is getting a bit weak and replacement would certainly help you.
 
Sud

Sud

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Guess i should mention the pump doesn't seem to be very "weak" to me... peaks between 22k and 23k psi still. but, i do have over 200k miles on this truck now.
 
DBUSHLB7

DBUSHLB7

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Sud said:
Guess i should mention the pump doesn't seem to be very "weak" to me... peaks between 22k and 23k psi still. but, i do have over 200k miles on this truck now.
Click to expand...

Don't know what your future plans are for the truck but if it is fairly strong still, keep it for a 2nd pump in a dual fueler setup and just pay the core charge of 200. That's what most used pumps go for around here. Sometimes 150.
 
A

AUSDMAX

AUSSIE DURAMAX FANATIC
Mar 21, 2013
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i think he may have ment drive gear... for the cp3 reluctor wheel has nothing to do with it :thumb:
 
Sud

Sud

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Lawrenceburg, KY
So this is basically a "plug n retune n play" swap?

I just wonder what i would actually gain? 3k rail pressure psi? which in turn, with good tuning, results in what, 10 hp on max effort tune? 20hp? 50 hp?


With increased rail pressure, do i risk springing a leak anywhere in the fuel lines? is this harder on the LLY Injectors?

Everything is basically stock, with the exception of the PPE Race valve and the Raptor 150 lift pump. no fuel or boost/intake modifications at this point. I don't see me ever actually "building" the bottom end of this engine. I don't drive it daily, it's more of a toy than a reliable vehicle... but i do occasionally tow light/medium loads with it.

Main reasoning for considering this - if i have to spend ~$300 for the fuel pressure regulator and dig into the engine that far, should i just spend a little more for an LMM (or LBZ) pump to up the rail pressure a touch? if it's not gonna gain me anything, i'll save a few hundred and just keep what i got and replace that FPR.

School me, fella's
 
chevyburnout1

chevyburnout1

Fixing it till it breaks
Aug 25, 2008
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You wont gain any rail pressure unless the tune is adjusted to command the higher pressures. If your holding 23k of rail pressure now your not going to see much hp increase if any, unless your tune gets adjusted to utilize the extra fuel the LMM pump can put out.
 
Sud

Sud

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May 15, 2012
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Lawrenceburg, KY
chevyburnout1 said:
You wont gain any rail pressure unless the tune is adjusted to command the higher pressures. If your holding 23k of rail pressure now your not going to see much hp increase if any, unless your tune gets adjusted to utilize the extra fuel the LMM pump can put out.
Click to expand...

Sud said:
So this is basically a "plug n retune n play" swap?
Click to expand...

:thumb:

With it retuned, what am I looking at?
 
Chevy1925

Chevy1925

don't know sh!t about IFS
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Oct 21, 2009
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Sud said:
:thumb:

With it retuned, what am I looking at?
Click to expand...

no one will be able to tell you that accept you tuner unless you feel like posting logs and such on here.

unless your loosing quite a bit of rail as it is now due to a worn out CP3 or other factors, putting a new one on isnt gunna do you much. you can make a lb7/lly reg hit 26k just as a lbz/lmm all by changing a few tables in a tune.
 
SmokeShow

SmokeShow

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Nov 30, 2006
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Lawrenceburg, KY
Amazing, I'm contemplating this exact same thing except I'm pretty sure my CP3 IS weak. Its been YEARS since I've logged my truck but I seem to recall, even back then, that my max-effort tune will pull pressure from 23k down to 17-19k but i do NOT hae a lift pump either & i think thats taken its toll on my CP3. Now the ol FPR lopes like a damn mod class cummins until it warms up. A little two-cycle in the fuel used to help but she sits so much the last 4-5 years that I think fpr is just sticky & no fixin it.

I have a cpl used stockers from lly & lbz & an original one of the first ATS "triple feed" modified cp3s. I'd rather just put a fresh lmm & reg. in it & be done with it.

The issue is so bad that my cruise control has a hard time regulating on downgrades. It bucks or jerks I'm assuming because the cruise control is trying to finely adjust the fueling (& consequently the speed) to keep at set speed but the fpr won't adjust so finely anymore & causes the jerking/bucking. It used to only do this on my highest tune (I've always assumed this is because it runs more pressure @ any given rpm?) but now its een doing it on my 3 & 4 tunes too. This is a new condition just like that loping at idle when cold.


This is way off topic but I've got to refine my tuning. I've got old dieselpilot v5 or v6 tuning from the good ol mcrat racing days & its just doesn't shift smoothly from 1-2 or maybe 2-3 at low speed (ie my neighborhood) & shifts to 5th waaay too soon. I've noticed my wife's stock truck (also an 02 like mine) also does the short shift to 5th & really lugs it. My tunes shift best at WOT.
 
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