67k miles on my 2006 KJ CRD. After 6 weeks of random P0093 error codes and limp mode, I replaced the fuel filter, fuel filter head (new style), and added a Mr. Gasket 12D lift pump. No more problems with P0093, but I now get a P0088 code with limp mode EVERY morning 2 minutes after starting her for my daily commute. Once I clear the code, it will typically run fine for another 2-3 minutes, throw P0088 again with limp mode. After clearing the P0088 for the second time every morning, everything seems fine for day.

P0088 - Fuel Rail Pressure Signal Is Above Maximum Limit

The Mr. Gasket Fuel Pump is rated at 4-7PSI, but I haven't measured the actual pressure. Bleeder / primer pump on the fuel filter is rock solid before starting (probably no air in the line).

I do have a Bluetooth OBDII adapter and run "Torque" on my Android phone. I've been monitoring visually monitoring the rail fuel pressure, but not logging it. Seems to top out at around 21.5k PSI.

Any ideas on where to start troubleshooting?

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Lyle Tanner - KC7IPY
2006 KJ Sport CRD (Diesel): Mopar skid plates, RRO OTT Lift, 245/75R16 Dunlop RVXTs, Mr. Gasket 12D Lift Pump, Samco Sport Turbo Hoses

Sounds like you have that bluetooth adaptor plugged into the diagnostic port at all times, correct? If so try pulling it out and see if your problem goes away. I don't know about your particular adaptor but there is lots of forum chat about a range of strange problems caused by running with scan tool plugged in.

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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

Tried leaving the OBDII adapter unplugged today. Still went into limp mode after a few minutes. This time I plugged in my traditional handheld OBDII scantool and still had P0088. Cleared the DTC and drove 45 miles. So it doesn't seem related to the the presence of my bluetooth OBDII adapter.

P0088 relates to an overpressure in the fuel system as measured in the rail. This code is monitored when the fuel system is in Mprop governing (i.e the PCV on the rail is closed) and points to an issue with your MPROP. Below are the possible causes:

1. Metering unit is stuck in open position
2. Zero delivery throttle clogged up
3. Metering unit without power due to electrical error
4. Pressure before gear pump too high (ex. with electric pre-supply pump with pressure relief valve)
5. Pressure after zero-delivery throttle too high

Our best guess is your fuel supply pump is overpressuring the inlet to the Bosch fuel pump leading to this fault code. Take this out of the system and see if the problem disappears. Good luck.

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Providers of wholly developed aftermarket solutions for the KJ CRD.
(248) 977 - 9531

My first instinct was that the increase fuel pressure behind the primary fuel pump was the source of the DTC, but then I figured 4-7psi was so insignificant compared to 23k psi. I guess I'll need to drop the input voltage on the lift pump and see if that helps. Time to brush up on what I learned about ohm's law in college.

I managed to grab the "freeze frame" associated with my P0088 error today.

Engine Load = 80.392 %
Engine Coolant Temperature = 145.4 °F
Intake Manifold Pressure = 33.214 psi
Engine RPM = 2,848 rpm
Speed (OBD) = 32.311 mph
Intake Air Temperature = 147.2 °F
Mass Air Flow Rate = 127.83 g/s
Fuel Rail Pressure = 25,248.17 psi

This was approximately 2 minutes after I started my morning commute. Obviously the 25,248 Fuel Rail Pressure is indeed too high. What is interesting is that after clearing the DTC, the computer seems to figure out how to keep the fuel rail pressure under 23.5k, as the highest pressures I see after the DTC is about 23.2k.

I guess I'll have to try out a resistor in series with lift pump tomorrow to drop the voltage (and hopefully the PSI) of the lift pump.