Misfiring/shaking '02 CL600.
 

I replaced the spark plugs, but I'm still getting faults from 3 cylinders. Any thoughts before I move to replacing the coils?

What were the faults?
Those 137 engines were a PITA to diagnose some times, were any of the red boots burnt? You replaced them all when you did the plugs, right?

how about oil in the harness?
if all your faults are 3 adjoining cyls, I'd look to a possible o2 sensor.

Yeah the good old M137. Anyone who's been around MB's for awhile understands why this engine didn't hang around too long. The CSO feature (cylinder shut-off) wasn't a bad idea, it just had some unintended consequences.

For those who don't know how it works, here it is. Under certain driving conditions, the left bank of cylinders was shut down to improve fuel economy. The resulting temperature and pressure change caused some blow-by, eventually putting enough engine oil into the intake manifold to start fouling the spark plugs. Believe it or not, a slight mis-fire on the M137 is almost undetectable to the driver. Because of this, the situation would gradually worsen, resulting in damage to the ignition coils.

The fix is pretty straight-forward. Replace the plugs, coils, and insulating boots. Then, remove the intake manifold and clean out all the oil to prevent a re-occurrence of the plug fouling. When this is done, drive the car to a shop equipped with SDS. With SDS, the sensitivity for mis-fire detection can be decreased by means of a software update, resulting in fewer "false alarms". Lastly, use SDS to disable the CSO feature (after all, CSO started the whole mess to begin with).

There are a few other scenarios, but back in the day, this was the most common. Since then, the ignition coils have been improved. In fact, I rarely see the newer version cause any problems.

Check to see if your coils havent been replaced already as well, the new ones part # starts with "275."

Pray to god your oil cooler doesnt start leaking either ;) Time to sell the car if that happens!

thanks for the reply.
 

the parts quote i got on the coil packs was 1250 per. i'd heard they were below a grand . . . guess not. great car, when it runs.

boots were burnt,
 

oil in the harness too. didn't get a fault on the O2 sensor though.

oil in the harness can cause some weird stuff. replace the leaking pressure sensor on the front of the left cylinder head asap and clean out as many connections as you can find with oil in them.

only getting faults from one side. any reason to replace the coil on the other side?

Exactly which cylinders are throwing the fault codes? Are they always the same, or is it random?

consistently 10, 11 and 12

We have a winner!!! Cylinders 10, 11, and 12 all report to the same O2 sensor. This is where you need to look first, although it's still possible that the coil assembly is the problem.

12 cylinders = 24 spark plugs, I guess.
Spark plugs change at dealership must be around $800 :) :-)