How can I diagnose a problem with the CP3 injection pump?

Last night I replaced my MPROP thinking it would fix my fueling problems.
At first it ran great and I thought I had fixed the problem.
But this morning it all went to doo doo again. Worse than before.
Rough idle, stumbling acceleration, would die and be difficult to restart.
It was like it was running out of fuel or didn't have enough fuel pressure.

Unplugging the MPROP seemed to fix it.
Started up great and ran smoothly.
But unplugging the MPROP also put it into limp mode with poor acceleration.

So what do I need to test or replace next to get it running right?

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U.S. Army Retired

Being that the Mprop also deals with pressure regulation, I think you'll end up wanting to swap the fuel rail out, and then the CP3 if that doesn't work. That is unless you can get the rail pressure sensor for reasonably cheap. Or, if someone knows enough to avoid the shotgun approach, that would be nice. I think it's one of the two sensors on the rail. One could cause the fuel pressure to be too low, and the other could lie to the ECU, either way, it could run like poop

oh, and maybe one of them caused your Mprop to go bad, hence the change in behavior with the Mprop change out. I wouldn't run it much on the new Mprop just in case. Someone will probably tell us that I'm wrong on this one, but just in case.

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05 CRD: H.D.S2 stat,WW Ironrock trilink&LCA's, OX rear,ARB front, 4.10's, ARB bumper, Suncoast,OME 3.5, JBA UCA,rock rails, Moabs&265/75 Duratracs, GDE tunes ,FFD fan,ARP's, 2 micron fuel, new valves,sasquatch battery tray & grid heater, tensioner relocated
Mech fan, VH & AC delete

I'll have to read back and see if you had already swapped either of the rail sensors, I remember you had done some testing on them

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05 CRD: H.D.S2 stat,WW Ironrock trilink&LCA's, OX rear,ARB front, 4.10's, ARB bumper, Suncoast,OME 3.5, JBA UCA,rock rails, Moabs&265/75 Duratracs, GDE tunes ,FFD fan,ARP's, 2 micron fuel, new valves,sasquatch battery tray & grid heater, tensioner relocated
Mech fan, VH & AC delete

Take a look at https://drive.google.com/file/d/0B8HRaB ... zZTUy/view

I do not recall that sidebrake ever finished it but it might help.

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Sold to LOST member my 05 Ltd, GDE Stg II turbo + TCM tune, SunCoast TC w. Transgo kit, Steiger window regulators, Samcos, Fumoto valve, 2nd gen filter head with Lub. Spec. bleeder, Hayden clutch & 11 blade fan, inverted spare, P-1 battery, BF Goodrich Long Trail TAs, Etecno1 glow plugs, timing belt at 50K miles/8 yrs

well you did what you had to do diagnosing this problem ,none of us have proper tools to check cp3 pump ,except bosch technicians . don't remove cp3 , i would look one more time back into fuel supply side , possibly small pice of debris floating back and fort inside fuel head , banjo fitting , ??? maybe disconnect lift pump run fuel line into fresh fuel from container not the tank , because your pump seams working ok and for same reason fuel del stop so as pump and again comes back to life, don't loose hope please , and good luck

Good point, the CP3 shows that it is probably good when you unplugged the Mprop

Those rail sensors are cheap in comparison and easy to change as well, and I can't see it as a bad thing to have them as new anyhow.

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05 CRD: H.D.S2 stat,WW Ironrock trilink&LCA's, OX rear,ARB front, 4.10's, ARB bumper, Suncoast,OME 3.5, JBA UCA,rock rails, Moabs&265/75 Duratracs, GDE tunes ,FFD fan,ARP's, 2 micron fuel, new valves,sasquatch battery tray & grid heater, tensioner relocated
Mech fan, VH & AC delete

Also I would remove that OEM fuel line between cp3 and ff head just you never know what is inside because we are still looking in fuel supply.

FYI: AUTOMETER and others make an in-line Rail Pressure Meter - disconnect the ECM connector from the Rail Pressure Sensor, plug the AUTOMETER connector to the Rail Pressure Sensor, reconnect the ECM connector to the AUTOMETER connector - reads the exact same data as ECM ~$125.00

DEMAND pressure is what ECM is controlling\regulating and wants to see on the rail
ACTUAL pressure is what ECM reads from the pressure sensor in the RAIL - should match within ~100psi - idle pressure is ~5000~6000psi
AUTOMETER reads ACTUAL pressure

I hadda nice set of DiPricol matched gages on my KJ, but lightning blast took them out, also, along with ECM, TCM, Front Control Module, Glow-plug Controller, ABS - only thing it didn't take out was the spark plugs controller

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'05 CRD Limited
Pricol EGT, Boost
GDE Hot '11; EDGE Trail switched
SEGR; Provent; Magnaflow;
Suncoast T\C, Transgo Tow'n'Go switch;
Cummins LP module, Fleetguard filter, Filterminder
2.5" Daystar f, OME r; Ranchos; K80767's, Al's lifted uppers
Rubicons, 2.55 Goodyears
Four in a row really makes it go

I ordered that gauge from amazon, came in yesterday.
Installation was a little bit more complicated than expected so I haven't installed it yet. It requires splicing wires into pressure sensor connector harness. Wasn't ready to do that yet.

So far, everything tells me that:
CP3 is good. Building pressure like it should.
MPROP is good.
Pressure Control Valve (PCV) on the fuel rail is functioning normally.
Fuel flow from tank all the way to the CP3 is good, no air.

The fault is intermittent. Engine starts up and drives great with plenty of power for about 5-10 minutes (sometimes longer) before it starts sputtering and stalling.

I'm now going back and rechecking all the wiring and connectors. It must be a intermittent short or loose connection somewhere.
All my previous tests showed the wiring is good.

_________________
U.S. Army Retired

I also discovered that there are two types of "limp mode" when dealing with fuel rail pressure problems.

1. A fault with the fuel rail pressure sensor (i.e. unplugged) results in the PCV on the rail being slammed shut. When using TorquePro this is displayed as fuel rail pressure (as demanded by the ECU) being set at maximum ~26000 psi.
With no sensed fuel pressure and a closed PCV, all fuel pressure is controlled by the MPROP. The ECU seems to use pre-programmed set points for controlling the MPROP.

2. A fault with the MPROP (i.e. unplugged) results in the MPROP being stuck fully open, sending the majority of fuel through the CP3 and up to the rail. The PCV functions normally regulating all fuel pressure. The ECU limits rail pressure to a max of ~12000 psi (as viewed with TorquePro) but will make adjustments as necessary.
While in this state, the ECU seems to ignore the pressure sensor and uses pre-programmed set points for controlling the PCV.

If there is a fault with the PCV the engine will not run at all. It will be stuck fully open, not allowing pressure to build in the rail.

Hopefully, when I get my pressure gauge wired up, I can see how well sensed rail pressure correlates to demanded rail pressure.

_________________
U.S. Army Retired

Replaced rail pressure sensor connector.
Installed AutoMeter rail gressure gauge.
Everything is looking good and running good.
Will take it on a good drive later to be sure.

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U.S. Army Retired