xliemx717

does anyone know which cylinder shutoff (overpressure valve shutoff) controls which cylinders? after replacing the oil cooler now the car has a constant misfire on cylinders 8,10.12. have replaced coil pack, O2 sensors, spark plugs, transformer, and MAF sensor same issue. I can only surmise that it is the cylinder shut off after reading many threads. however, even after unplugging the cylinder shut offs, still same issue. need to fix so I can get rid of this money pit once and for all!!!

kraut56

Any codes? The WIS procedure calls for clearing all codes after cylinder head re-installation.
As far as I know, the front shut off valve does cyl. # 7 - 9, and the rear valve does # 10 - 12, so that does not jive with your misfire problem.

Did you do the valve timing check as per WIS?

xliemx717

timing is correct, dots lined up on cams and cylinders. car starts right up no problem, has plenty of power after idle, just will not idle as this is when it misfires. funny thing is, thought I had the shut off valves switch, so reversed them, then had misfires on cylinders #7,9 and 11. so I am confused if one controls front three (which makes sense) but switching the shut off valves just puts the misfire on the even cylinders.

kraut56

Do you have/follow the WIS?
Do you have DAS/STAR?
It clearly states Y80/1 cylinder shut-off valve for cyl #7 - 9, and
Y81/1 cylinder shut-off valve for cyl #10 - 12.

Was the engine in the required 30 degree crank position before head removal with cams in the base position?

Again did you have any codes or did you clear them?
MB advises on line 34 of cylinder head removal to read DTC and clear all fault memory.

I would not have changed the ignition coil pack module that quickly.


It is confusing that you can switch between odd/even cylinders misfire - if you have DAS/STAR go into the ignition inverter module and check for faults.

xliemx717

engine was at 30 degrees at instructed by WIS, there were no codes/faults before removal of the cylinder heads. unfortunately I do not have DAS/STAR if I did I would turn off the cylinder shut off. If I had a .45 pistol I would put the car out of its misery.

kraut56

I have been advised by an MB California rep that following a cylinder head removal/installation (with all the harness disconnects) of this 12 Cyl. engine you must do a STAR/DAS clearance/reset of the engine control module. (obviously an OBII reader will not do).

From your experience it appears the sensor monitoring by the engine controller software is "off the normal".

So, before you change any more parts, I believe it is prudent to find somebody with a STAR/DAS system (I have my own, and you should be able to find someone at a non-MB garage with one).

Save that silver .45 bullet for some later time.

I invite comments about de-activating the cylinder shut-down feature - does anybody out there know how to do that with DAS???

Obviously the gas saving is not worth the hassle.

xliemx717

problem fixed car will be sold, bullet still in chamber waiting for the right moment, which could be soon!

kraut56

So for my very personal interest:

a) what was the identified problem cause, and,
b) how was it fixed?

NB: I'm just about to put mine back together again.

At least keep the safety ON on that .45

xliemx717

I wish I could give you a "this " was the problem. However, this is what I did, took it apart to check timing, check the timing through 5-6 complete revolutions of the engine, it was fine, put everything back together, started car and no CEL. no misfire or anything car will peel tires from start in all gears. beats the crap out of me why it decided to work, when I did absolutely nothing except check the timing and put it back together.

kraut56

Well, after all that work you might as well enjoy the car!

BTW - what did you do with the old ignition module (coil pack)? Do you still have it ?

That old NA V12 actually can burn rubber pretty good, so keep the .45 in the night table drawer for now.