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 Post subject: 2006 CRD limp mode, high fuel pressure when w
PostPosted: Thu Feb 02, 2023 3:06 am 
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I bought a 2006 KJ CRD not running for cheap from an estate. The widow said it was the deceased's pride and joy. It looks like it had a bunch of work done to it but had not run since the work was done...looks brand new under the hood. It has had a full EGR delete, with the FCV removed. Scanner shows P0403 and P1140 with CEL on, so it must not have had any tune done to it. In-tank fuel pump was installed, and is working. The carpet in the back was pulled up, and the plastic trim was not in place, so the KJ may not have ever been driven since the in-tank pump was installed.

Here's what I have repaired:

1) all 4 glow plugs were replaced. All of the old ones were non-functioning.

2) ABS module had a short that would blow the fuse under the hood as soon as the big plug to it was connected. I replaced the module with one from a wrecker. The fuse doesn't blow, but I'm getting the "Vehicle Configuration Mismatch" code and another one. I am scheduled to have a dealer flash the ABS module to the vehicle to hopefully fix that issue. Currently, the ESP/BAS malfunction lights are illuminated.

3) The wires to both rear ABS sensors were pulled out of the connectors at the wheels. I fixed the wires and now I'm getting appropriate speed readings from each wheel on my scan tool with Live Data.

As I mentioned, I have a scan tool that can show live data (which is the only way I would know how to fix any of these things).

The engine starts perfectly hot or cold, and runs normally (compared to my other 2006 KJ CRD that I've been driving for a year) until the fuel temperature reaches about 60 degrees F, at which point the Fuel Pressure climbs above the Fuel Pressure Setpoint, causing a limp mode.

I can clear the codes, but I get back a variable mix of P0088 (Fuel Rail/System Pressure - Too High) P0090 (Fuel System Leak Detected Large Leak).

When warm, on startup, the measured fuel pressure follows the Setpoint for about 3 seconds, and the rises to 1500psi above the Setpoint. If I rev the engine or put it under any load, the measured fuel pressure can run over 4000psi about the Setpoint. When the vehicle enters Limp Mode, fuel pressure is limited to about 18000psi, and boost is limited as well. Moreover, when it is in Limp Mode, the Measured Fuel Pressure exactly follows the Fuel Pressure Setpoint...follows it suspiciously closely. I don't know what that means... apparently one of the two pressure regulators can take over and limit the fuel pressure, but why doesn't it do before? Or does the ECM ignore the feed from the Fuel Pressure Sensor and go to some default value that is assumed based on RPM and throttle position?

I have swapped out the Fuel Pressure Sensor, Fuel Quantity Solenoid, and Fuel Pressure Regulator (on the end of the rail) with new parts, and the symptoms don't change at all.

I tested the voltage at the connectors for both the Fuel Quantity Solenoid and the Fuel Pressure Regulator, and I did not detect a change in voltage right after startup that would track with the change in Fuel Pressure.

I have pored over dozens of posts on this forum about fuel pressure issues and can't find any wisdom pertinent to my issue.

Thanks to all of you who put so much time into this forum to help folks like me.

Phil


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 Post subject: Re: 2006 CRD limp mode, high fuel pressure when w
PostPosted: Thu Feb 02, 2023 4:47 am 
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What about the Cascade/Overflow Valve on top of the CP3, sounds like you have changed most everything else.

Regulates lubrication to internal parts of the injection pump and regulates the fuel pressure to the fuel quantity solenoid valve on the back of CP3 injection pump. Also, controls the amount of fuel being returned to the fuel tank via the fuel return line.

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 Post subject: Re: 2006 CRD limp mode, high fuel pressure when w
PostPosted: Thu Feb 02, 2023 11:43 am 
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No, I have not done anything with the Cascade Overflow Valve, but it seems very plausible that it could cause a problem.

Judging by it's placement on the diagram you supplied, it looks like its hidden under the alternator mount?

I actually didn't find replacing the Fuel Quantity Solenoid to be that difficult, but the COV has to come straight up and out.

Am I so lucky as to be able to change the COV without removing the alternator and mount?

Thanks very much for your response, WW.

Phil


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 Post subject: Re: 2006 CRD limp mode, high fuel pressure when w
PostPosted: Thu Feb 02, 2023 2:38 pm 
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I went out and looked at my Jeep; I see no way to gain access to change the Cascade Overflow Valve without removing the alternator and its mounting bracket. :( :banghead:

A couple of thoughts: :idea:
1. I hope the parts/sensors you replaced are all Bosch or Mopar OEM parts. Cheap knockoffs can cause all kinds of problems.
2. What is your fuel feed pressure to the CP3? If your supply pump feed pressure is excessive, it can cause overpressure problems in the CP3 and in the fuel rail.
Hopefully some of this will be helpful in finding your problem!

Read this:
Quote:
Supplying Fuel to the CP3 Injection Pump
Being a constant displacement pump means that it you can't hook just any supply pump up to it. Whereas some injection pumps can tolerate a large difference in flow rates to/through it with relatively little pressure change, the CP3 cannot. If you try to push too much fuel through the CP3 (supply pressure), the discharge pressure will skyrocket to very unsafe levels and the rail pressure will increase accordingly way beyond design pressure. There are no internal pressure relief valves in the CP3, only a direct feed to the internal supply pump. Conversely, if there isn't enough flow to it, the pressure will drop and the internal supply pump will create a vacuum (suction) in an attempt to try and supply itself enough volume of fuel to satisfy demands.

More information on the Cascade Overflow Valve:
Quote:
CASCADE OVERFLOW VALVE
DESCRIPTION
The COV is located on the front cover of the high pressure pump.
The Cascade Overflow Valve has three functions:
- regulation of lubrication fuel to the internal moving parts of the high-pressure pump
- regulation of the fuel pressure being supplied to the Fuel Quantity Solenoid valve
- return excess fuel to the fuel tank
This regulated internal pressure is known as housing pressure, and is determined by engine displacement and power requirements - the 2.8L CRD requires 5bar (73psia)
For comparison, the 5.9L 6-cyl Cummins CRD requires 12.41bar (180psia)

OPERATION
The COV has a spring-loaded center spool-piece that has a drilled channel with three passages: one for initial low-pressure lubrication, one for lubrication at housing-pressure , and one for overflow. The valve is operated in three stages based on the level of pressure at the inlet.

Stage 1
When the fuel pressure entering the tip of the COV is between 0 and 3 bar (44psia), pressure is too low to overcome
regulator spring tension and fuel flows through the center channel, only . This passage always allows fuel flow through to the pump center-ring and lubricates the pump bushings and internal moving parts. This circuit also allows air to bleed during initial cranking and returns the air to the fuel tank.
The COV is in Stage 1 during cranking, only.

Stage 2
When the fuel entering the COV exceeds 3bar (44psia), but is less than 5bar (73psia), the spool-piece
moves against spring tension aligning a second passage for lubrication purposes.
Stage 2 can be reached during cranking and initial start up.

Stage 3
When fuel pressure exceeds 5bar (73psia), the spool-piece aligns with the overflow passage. This stage
relieves the pressure into an overflow circuit that sends the fuel back to the inlet side of the gearotor pump, thus limiting maximum fuel pressure to 5bar (73psia).
Lubrication fuel continues to flow through all channeled passages during this stage.
Excess fuel is sent back to the fuel tank through the fuel-return circuit
Stage 3 is reached at over-pressure

_________________
Supporting Vendor and Moderator of LOST
05 Jeep Liberty CRD Limited :JEEPIN:
Ironman Springs/Bilstein/Shocks
Yeti StgIV Hot Tune
Week's BatteryTray
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SunCoast/Transgo
Carter Intank-pmp
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 Post subject: Re: 2006 CRD limp mode, high fuel pressure when w
PostPosted: Thu Feb 02, 2023 4:35 pm 
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I looked at my parts engine and came to the same conclusion: remove cam timing assembly, timing belt, alternator, cp3 pump bracket and pump, and remove cp3 from mounting bracket to get at the COV. Ughh.

I think i might go after the aluminum mounting bracket with a carbide burr...I wouldn't have to remove very much metal from a shoulder on the mount to be able to get a socket on a wobble extension on the COV. I don't think it would weaken the mount unreasonably.

To answer your other questions...yes, i used Bosch parts from ID Parts...well, the Fuel Quantity Regulator was on my parts engine and worked correctly... It was a head gasket that took that engine out. The Fuel Pressure Sensor and Regulator were both Bosch. FWIW, the suggested Fuel Pressure Regulator from ID Parts was made by Standard, bit they offered the Bosch part, saying it was for a Duramax but would fit the VM. It did, and was like $200 cheaper than the Standard.

As for inlet fuel pressure, I warmed the engine up to get the limp mode happening, then removed the relay for the in-tank pump, cleared the codes, and it made no difference...fuel pressure climbed way above the Setpoint with a few seconds after startup. Thanks again.


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 Post subject: Re: 2006 CRD limp mode, high fuel pressure when w
PostPosted: Thu Feb 02, 2023 11:45 pm 
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BREAKTHROUGH!

So I experimented with the fuel temperature sensor. The default fuel temperature value when the ECU senses either an open circuit or a short circuit from the fuel temperature sensor (located on the fuel filter housing) is 174.9 degrees F.

With the fuel cold, I unplugged the fuel temperature sensor and the fuel pressure did exactly what it's been doing when the fuel temperature reaches about 60F: on startup, the Fuel Pressure follows the Setpoint for a few seconds and then rises to way above, after which the Fuel Pressure Regulator (on the rail) takes over to regulate fuel pressure, limiting it to around 18000psi.

So with the fuel at 70F, I put a 10k ohm resistor in the Fuel Temperature plug, fooling the ECU into thinking that the Fuel Temperature was 10F, and the engine ran normally with no limp mode.

I compared the voltage coming from the Fuel Temperature sensor at a given temperature on this problem KJ with my daily driver KJ, and they track properly: the Fuel Temperature sensor on this problem KJ is working properly.

So the question is: why is the ECU putting the engine into limp mode when the Fuel Temperature is only 60F? I guess it's not a big deal since I now know how work around the problem, but it's still a mystery. Could it be a bad tune on the ECU? I have no experience with tunes on a KJ, and I assumed this problem/project vehicle had not been tuned because its still showing the codes for the EGR delete. Mysterious.

Phil


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 Post subject: Re: 2006 CRD limp mode, high fuel pressure when w
PostPosted: Fri Feb 03, 2023 1:52 am 
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That doesn't make a lot of sense to me. Why would cold fuel temperature cause increased fuel rail pressure spiking?
Have you checked the wiring and connectors for the fuel temperature sensor?
What about grounds? FSM shows the fuel temperature sensor, ambient air temperature sensor, coolant temperature sensor, and a multitude of other items all use the same ground circuit (splice S154 in area near starter motor) and the ground circuit goes to the ECM pin 65 in the C1 connector.
A bad ground could be giving the ECM bad data especially on resistance type sensors!

Check the ground right under the cowl rubber flap about the brake booster and the ground under the power distribution center & battery on top of the fender. Both of these are very important ground and if either one of them is bad, it can cause all kinds of problems.

Also, try unplugging the fuel heater on the fuel filter module.

Image

_________________
Supporting Vendor and Moderator of LOST
05 Jeep Liberty CRD Limited :JEEPIN:
Ironman Springs/Bilstein/Shocks
Yeti StgIV Hot Tune
Week's BatteryTray
No FCV/EGR
Samcos/ProVent
SunCoast/Transgo
Carter Intank-pmp
2mic.Sec.Fuel Filter
Flowmaster/NO CAT
V6Airbox/noVH
GM11 Bld.fan/HDClutch
IronrockArms/wwdieselMount

98 Dodge Cummins 24 Valve


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 Post subject: Re: 2006 CRD limp mode, high fuel pressure when w
PostPosted: Sat Feb 04, 2023 4:15 pm 
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Thanks. I will check those grounds for sure. Bad grounds are my go-to any time there is some group of illogical, seemingly urelated symptoms.

I was unclear in my last post. Fuel rail pressure doesn't spike because the fuel is cold. Rather, based on the behavior of the fuel pressure (Setpoint vs. measured), when the ECU detects out-of-spec fuel temperature (like when the sensor is unplugged and the ECU defaults to 174.9F) the Fuel Pressure on startup climbs and then either the FQS or the FPR or both takes over and cuts the fuel pressure back to a much reduced level.

When I fool the ECU into thinking that the fuel is ice-cold, no matter what temperature the fuel actually is, the control of fuel pressure on this Jeep remains proper.

I don't know at what fuel temperature the ECU is supposed to protect the engine by dropping power (by limiting boost, fuel pressure, and fuel delivery, presumably), but on this KJ, the computer calls for Limp Mode above about 60F fuel temperature.

The Fuel Temperature Sensor appears to be reading the fuel temperature correctly, based on my scan tool readings of temperature and voltage.


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