On saturday my Jeep went into limp mode and threw a P0090 code at me.
The code indicates that the Fuel Quantity Solenoid (MPROP) on the CP3 is either unplugged or has gone bad.
I replaced the MPROP back in July when I was having rail pressure problems.

So far, I have done continuity checks at the harness connector and that seemed to indicate an intermittent open circuit at the connector. I have replaced that connector but the problem still persists.

I do not believe that the MPROP is bad.
I did a resistance check across the pins on the MPROP and got 3.5 ohms. Not an open circuit and that seems to be good resistance for a solenoid. But the book does not give any value as to what the resistance should be.

The book says to jumper the pins in the harness connector to see if that throws a P0092-short to ground. That did not happen. Still got the P0090 code.
Book says that in this case the ECM is bad.
I'm not sure how the ECM could be bad as this P0090 code is the only symptom and the vehicle is drivable but with reduced power because of limp mode.

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Anybody have any idea of what the internal resistance of the MPROP should be?

I am going to do more testing this afternoon. Probably gonna have to dig deeper into the wiring harness.

If anyone has any suggestions for testing or where else I can go for help, please let me know.

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I'd guess harness, myself.

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Don't know what the resistance should be but 3.5 sounds reasonable.

Solenoid drivers are discrete interface circuits and can fail without affecting any other functions of the ECU. They're a fairly common failure point.

How's your idle?

Have you seen this?

http://oregonfuelinjection.com/pdf/jeep ... nostic.pdf

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It idles just fine.

I have a fuel rail pressure gauge and it shows that pressure is just fine.

The only problem is the reduced power due to limp mode.

I've read that document several times and it has not been much help.

The last time I had this problem (July) it was a P0193 code that was caused by a intermittent open circuit at the rail pressure sensor harness connector. I replaced that connector, installed the pressure gauge, and all has been fine till now.
That problem was difficult to track down and lead me to replace the rail pressure sensor and MPROP.

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Well, it appears that I have fixed it somehow.

There was good continuity all the way through the circuit. From ECU to MPROP and back.
But voltage on the hot lead to the MPROP was a bit low or intermittently low.
So I re crimped my connections and kinked the pins at the ECU. The code has gone away and full drivability has returned.

Normally I wouldnt use crimp connectors but its in a tight place and I dont have a steady hand for working a soldering iron in there.


It was a good day today. Not only did I get my Jeep running again but I got to take my daughter to her first NFL game AND the Jags WON!

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