Lmm rail psi trouble

Bonestock

Bonestock

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Aug 9, 2010
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Here is one for the gurus. I have a buddy with an 09' lmm. He is getting reduced engine power on the dic. His truck has a dsp5 tune , fass hd-150 and a 5" diamond eye exhaust system. I logged the truck on a test drive for rail psi. When demanding 26k it actual rail is 17k. Just for shits & grins I loaded the stock tune in & it did the same thing 26k commanded & 17k actual. I then took an injector balance test & all were perfect. I then used the dvt tool to ramp up rail psi. I was able to get a little rattle out of the injectors but not much change when commanding 160 mpa max. I am damn sure you can kill a running engine ramping up rail if it has a good cp3. Any ideas before the cp3 comes out?
 
nvrplzd

nvrplzd

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Sep 3, 2011
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Does he have a fuel rail plug or a shimmed fprv?

That would be my first guess since it wasn't mentioned.

It doesn't matter how much fuel you supply if it's getting vented and can't hold pressure.
Also if it IS shimmed, look into reshimming (just to make sure) because the spring can still lose tension over time, that could potentially cause a release in pressure as well.

Just my 0.02
 
Bonestock

Bonestock

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Aug 9, 2010
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nvrplzd said:
Does he have a fuel rail plug or a shimmed fprv?

That would be my first guess since it wasn't mentioned.

It doesn't matter how much fuel you supply if it's getting vented and can't hold pressure.
Also if it IS shimmed, look into reshimming (just to make sure) because the spring can still lose tension over time, that could potentially cause a release in pressure as well.

Just my 0.02
Click to expand...

He was shimmed but I replaced it with ppe race valve, no difference.
 
AKlowriderZ71

AKlowriderZ71

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May 14, 2012
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When my LB7 did that, the CP3 was bad. Confirmed it with a bottle test before making the purchase.

I know they aren't the same, but I don't think they are THAT much different....
 
nvrplzd

nvrplzd

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^yeah i'd definitely do a bottle test before purchasing a new cp3.

It's a long shot for sure but does he still have the factory filter head? It's more common with the older trucks but sometimes I've heard of the lines coming from the filter head collapsing under pressure due to age. (i'd say probably start pricing cp3's though)
 
Bonestock

Bonestock

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Aug 9, 2010
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nvrplzd said:
^yeah i'd definitely do a bottle test before purchasing a new cp3.

It's a long shot for sure but does he still have the factory filter head? It's more common with the older trucks but sometimes I've heard of the lines coming from the filter head collapsing under pressure due to age. (i'd say probably start pricing cp3's though)
Click to expand...

Still has factory filter head. The thing that concerns me is that the truck seems like it looses prime and is hard to start @ times. Which leads me to believe it is getting air in the system somewhere somehow. Possible filter head orings leaky but seems like there is some common ground there. I will bottle test it and see if it is returning access amount of fuel.:thumb:
 
jnieberlein

jnieberlein

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Aug 17, 2009
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Bonestock said:
I haven't but it looses rail on the stock tune? I would think the cp3 should be able to work even if the fass pump was turned off?
Click to expand...

I lost power to my airdog and the truck would run, I first noticed there was an issue when I tried to get on it and truck fell on its face, it would be worth a check, the cp3 was pulling fuel through a 2 micron cat filter and a non running lift pump she worked but not well, wouldn't hurt to check it for power also had a few miles on the filters and that probably didn't help either
 
Bonestock

Bonestock

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Aug 9, 2010
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jnieberlein said:
I lost power to my airdog and the truck would run, I first noticed there was an issue when I tried to get on it and truck fell on its face, it would be worth a check, the cp3 was pulling fuel through a 2 micron cat filter and a non running lift pump she worked but not well, wouldn't hurt to check it for power also had a few miles on the filters and that probably didn't help either
Click to expand...

I will check it. It has fairly new filters.
 
SSchmi5519

SSchmi5519

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Oct 19, 2008
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The factory fuel head can crack(hairline) causing it to slowly lose prime. Does he have a lift pump? Can you check lift pump psi at the test port in the engine bay? will tell you if theres a restriction in front of the cp3 at least..
 
Harbin_22

Harbin_22

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Dec 4, 2010
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SSchmi5519 said:
The factory fuel head can crack(hairline) causing it to slowly lose prime. Does he have a lift pump? Can you check lift pump psi at the test port in the engine bay? will tell you if theres a restriction in front of the cp3 at least..
Click to expand...

Boy Steve, you really didn't read through the thread :D
 
Harbin_22

Harbin_22

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Also the DVT for LMM's doesn't work half the time. A lot of times, it might change something for a split second and then go back to where it is supposed to be. You will need to look back at the log to see if it actually upped the rail psi. But you should hear it rattling like crazy if it does ramp up rail
 
SSchmi5519

SSchmi5519

LLY Cult Leader
Oct 19, 2008
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Or maybe a bum WIF sensor thangy? Ive seen those go bad, although the one i saw had a very slow fuel drip. Never made it to the ground but was on the frame...
 
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