M2 MBE 900 carbon packing -- Is a new engine the only solution?

Our 2009 M2 with an MBE 926 with around 125,000 miles wouldn't start recently after sitting for several months. It was towed to the dealer, who reported that it needed a new engine ($41,000) because of carbon packing. Any thoughts on the following diagnosis (and ideas about things to try) would be very appreciated.

Troubleshoot crank, no start condition:

VERIFIED CUSTOMER COMPLAINT, TRUCK WILL CRANK BUT NOT START. GOT LAPTOP AND CONNECTED WITH DL. NO FAULTS. HOOKED UP AIRLINES AND AIRED TRUCK UP. PUSHED INTO SHOP. GOT FUEL SYSTEM PRIMER AND HOOKED UP. PRIMED FUEL SYSTEM AND TRIED TO START WHILE PRIMING. STILL WOULDN'T START. MONITORED FUEL COMPENSATION PRESSURE, ACTUAL FUEL MASS, AND KW/NW SIGNAL WHILE CRANKING. FUEL COMPENSATION PRESSURE GOT UP 50 PSI (REPRESENTS LOW SIDE FUEL PRESSURE). 50 PSI IS GOOD CRANKING PRESSURE. KW/NW SIGNAL WENT FROM OFF TO ON, WHICH IS CORRECT. ACTUAL Ft:EL MASS WENT OVER 100 MG/ST, ACTUAL FUEL MASS GOT EXCESSIVELY HIGH AND ENG[NE STARTED FUEL KNOCKING. EXHAUST HAD GAS SCENT TO IT. RAN RELATIVE COMPRESSION TEST, FOUND CYLINDERS 2,3, AND 4 WERE VERY LOW. NEED TO RUN MECHANICAL COMPRESSION TEST TO VERIFY CYLINDERS ARE NOT DAMAGED DUE TO OVER FUELING. MECHANICAL TEST CONFIRMED MULTIPLE CYLINDERS HAVE VERY POOR COMPRESSION. A NEW ENGINE IS NEEDED.

Troubleshoot low compression:

PUT JUMP STARTER ON TRUCK TO GET TO CRANK EVEN CRANKING YOU CAN HERE WAY IT CRANKS LOW ON COMPRESSION RINGS ARE STUCK BECAUSE OF CARBON PACKING (OIL) YOU CAN PULL PISTONS AND CHANGE RINGS IF CYLINDERS OK.

 

Opened up meaning replacement? Or opened up meaning take the cylinder head off, drop in some kind of solvent to dissolve the crud that's fouling the piston rings, and reassemble? Or opened up meaning pull the pistons from the crankshaft, then clean and replace them?

And would there be any reason that Mercedes might help us with the cost on this?

Thanks.

 

Many thanks. Will check with the higher-ups and see how they want to proceed.

 

Thanks for all this great info. I should point out that this engine is in an ambulance, which does (or maybe I should say "did") a lot of short runs and spent a lot of time at idle, which is necessary to keep the heat or ac running until the crews return with a patient (for what it's worth, the unit even had a special switch installed that would allow it to stay running after the key had been removed while the crew was providing medical care on scene, with the provision that if someone hopped in and tried to steal the unit, the engine would shut down the first time the brake pedal was pressed).

It did get spooled up pretty hot once in a while to do a regen, but apparently not frequently enough (I can only imagine what it would have been like had we elected to bypass the regen system which EPA allows on emergency vehicles).

With all of that said, one would think that Mercedes would design an engine that could put up with any operational style and not just assume that everybody was going to be running for hours non-stop every day.

And I still don't get why this problem appeared all of a sudden after the vehicle had sat unused for several months.