LB7 no suction @ cp3 pump

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mssrgraham

New member
May 7, 2016
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Help.....
LB7 DURAMAX PRIMING PROBLEM.
I can prime the system with the fuel filter head priming pump but it will not hold pressure, like, I can pump it up hard, then after a minute or so it loses pressure. Bearing in mind that it's a brand new priming pump and that there's no problems with the lines back to tank, and no air intake in the line to the pump. I was wondering if there's a problem with the cp3 pump or fuel pressure regulator maybe, as I can take the delivery line off to the cp3, put my thumb over it, and there's no suction at all.
I have taken the oil filler tube out and had a look to make sure that the pump gear isn't spinning on the shaft, and it's all good.
I have put a gauge on the Schrader valve, pumped the gauge up to 14 psi, then watched it lose pressure.
My question is, besides the gears in the pump, is there any thing else that would influence a loss of suction? Does the fuel pressure regulator play a part in this? I'm trying to establish if this problem is electronic or mechanical.
So at the end of the day I guess I have two problems, filter head not holding pressure, and no suction from the cp3 pump.....would/could these two problems be related?
Any help on this matter would be appreciated, as its really doing my head in.
 
Burn Down

Burn Down

Hotrodder
Sep 14, 2008
7,093
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48
Boise Idaho
Primer doesn't keep pressure on it when your done pumping, it slowly bleeds down. Which hose are you checking for suction? The one off of the vertical fitting on the cp3 or the one pointed to the back of the truck?

How many miles on the injectors and fuel pump?
 
M

mssrgraham

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May 7, 2016
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Reconditioned pump and injectors, and the line I was checking was the one going out of the filter head to the horizontal fitting on the back of the pump....the one pointing to the back of the truck.
 
Awenta

Awenta

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Sep 28, 2014
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Like said the primer doesn't stay hard it bleed down. That's normal.

Does it start and run? What's the problem?

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M

mssrgraham

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May 7, 2016
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The injectors I reconditioned myself and had them bench tested at my local diesel repair shop. The pump was done by Pensacola Diesel...
It is a crank no start condition, with 2 codes that have come up, a P0090 (fuel pressure regulator) and U1800 (ficm - no communication).
The troubleshooting flow chart says that if both of these codes come up together, to go straight to the ficm.
I have replaced it, but still no luck.
Everything on this Truck from the filter head through to the injectors is new or reconditioned. The only item I haven't changed out is the ECM. The wiring harness looks fine, no chafing anywhere, although I haven't yet check it for continuity, just visually.
I am beginning to wonder if there's a drama in the pump, hence the questions in the original post...
 
TheBac

TheBac

Why do I keep doing this?
Staff member
Apr 19, 2008
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How the heck did you "recondition" your own injectors? If you meant "rebuild", then that is not a DIY project. What did the shop's bench test tell you?

Id be looking at the wiring harness to the FICM if you replaced it and no change, but the reconn'd CP3 from Pennsacola concerns me. Their reputation in the Dmax community is not the greatest.
 
IOWA LLY

IOWA LLY

Yes, its really me
Feb 23, 2007
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Pensacola Diesel and at home reconditioned injectors says it all.

As Tom said, not a diy project.

Start over. This time buy good parts.

And before you start whining about not being able to afford good parts go take a handful of $100 bills and burn them. That is the exactly what your doing buying cheap imitation fuel system parts.......

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M

mssrgraham

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May 7, 2016
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Just bear in mind I don't live in the USA, so getting these parts is always a hassle because of the distance....I'm in outback Queensland, Australia. That's why I'm trying to troubleshoot this problem by asking you blokes...so I don't spend shit loads of cash.
My scan tool doesn't read rail pressure, but like I said, I put my thumb over the delivery line from the fuel filter head, turned it over and there is no suction.....so before I go and pull this thing apart I was asking if there's anything else that would influence the loss of suction other than the pump itself.
 
Awenta

Awenta

Active member
Sep 28, 2014
4,090
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mssrgraham said:
Just bear in mind I don't live in the USA, so getting these parts is always a hassle because of the distance....I'm in outback Queensland, Australia. That's why I'm trying to troubleshoot this problem by asking you blokes...so I don't spend shit loads of cash.
My scan tool doesn't read rail pressure, but like I said, I put my thumb over the delivery line from the fuel filter head, turned it over and there is no suction.....so before I go and pull this thing apart I was asking if there's anything else that would influence the loss of suction other than the pump itself.
Click to expand...
You should have asked before you wasted money on crap. Especially when you have to pay a premium. Any of the good vendors would ship to you or even some members on here. Pensacola is know garbage and I wouldn't put their parts on my lawn mower. A better scan tool would benefit you.

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Burn Down

Burn Down

Hotrodder
Sep 14, 2008
7,093
28
48
Boise Idaho
Efi Live is in your neck of the woods, or GM Tech 2 the china one, is very affordable and seems to work fine.http://www.sicotool.com/2014-gm-tech2-with-candi_p62.html

Check the wiring where it is strapped down to the Ficm mounting bracket, the LLY likes to rub through there and short out, I guess the LB7 could do it as well. First thing is to get rid of those codes then we can move on to your CP3 and Injectors. Did you just put tips on the injectors?
 
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DefiantArms

DefiantArms

Limp Mode Cowboy
Jan 28, 2016
897
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St. Augustine, FL
out of my own ignorance and curiosity does the Cp3 have a clutch that although the serpentine is turning the pully a wire problem would be preventing the pump from pumping?
 
Awenta

Awenta

Active member
Sep 28, 2014
4,090
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CT
DefiantArms said:
out of my own ignorance and curiosity does the Cp3 have a clutch that although the serpentine is turning the pully a wire problem would be preventing the pump from pumping?
Click to expand...
Gear driven. Belt has no bearing on the cp3

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