I know this vehicle is a bit new for this forum - but I know there are a few techs here that may have some insight. The WIS for the subject vehicle calls for removing the intake manifold to perform a spark plug change. The first step in the WIS is to remove the bulkhead (firewall insulation panels). The photos in the WIS seem to confirm that the bulkhead has to come out to remove 2 bolts at the rear on the intake manifold. The bulkhead is in 3 parts, L, R and center. The sides come out easily. The center section is ridiculously difficult!!

There are folks on the internet that have done this job without removing the intake manifold. Even though I normally am religious about following the WIS at this point I am leaning towards trying their methods.

Has anyone done this on this vehicle? Do shop techs really remove the intake manifold? Getting the bulkhead out is so difficult it seems to me that any tech would avoid it.

can you reach plugs from below with extensions and swivels?

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

No.

If under pans removed?

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

No. The problem is that the coils/connectors, etc. are unreachable without removing something. The WIS way is to remove the intake manifold. The internet method involves removing the air cleaner housing on the right side (easy) and the ECU and its mounting bracket plus disconnecting and moving various sections of wiring harness on the left side. This must take place before you can even see the coils. Trying to do that from underneath is not possible. I know the internet method sounds fairly easy, and in fact it may be the preferred method, but when you are in there it doesn't look so simple.

I tried to remove the bulkhead per WIS but it is really tough. I got all the fasteners out but trying to remove the wiring harness attached to it finally caused me to stop and assess. I cannot imagine a tech using this approach. Getting the fasteners back in really reinforced that opinion. I did all that just to see if it was doable before I actually bought parts, etc.

I've been working on M-B engines and cars since 1963 and always found them fairly easy if you have some patience. This - not so much.

Vince, try searching for a You Tube video of spark plug replacement for your ML350. Most DIY jobs that I perform on our MB vehicles have You Tube videos that I view beforehand.

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Fred Hoelzle

No luck there Ferdman. There is info on removing the intake manifold on a sedan, but there is room at the rear to work. Not the case on the W166 ML. Folks, including me, have been trying to figure this out since the W166 came out. Mine is now due. I was at the dealer yesterday and we went through the WIS and cannot find anything on removing that panel. M-B seems to think it is self-explanatory.

The top part of the manifold does come out before you "get access." That's a joke and you'll get it if you actually pull off the job. The spark plug connectors most likely will not want to come out too. Don't be surprised if you need to replace some due to removal damage.

Don't recall doing a 166 specifically because I try to avoid working on MLs like the plague but I'd avoid pulling the center firewall panel at all costs.

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Thanks. Too bad it is suchh a pain. It has been a flawless vehicle for us - never had a warranty item. But this job looks like it will sour the experience.

When I look at WIS, it lists removing the portion wall only for the 251 (R-Class). Also, it seems like it is possible to do the job by removing the air box on one side, and a heat shield and computer box on the other (probably also need to be very dexterous).

https://mbworld.org/forums/m-class-w166/632475-60k-service-w-spark-plugs.html

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Prost!

I believe you are referring to Job AR15.12-P-2003GQ, "Remove/install ignition coils". It does not call for removing the "bulkhead" on the W166. However, Step 3 is to "Remove intake manifold". That is where it gets ugly. Job AR09.20-P-1961GQ, "Remove/install intake manifold" Step 6 is to "Remove bulkhead (78)".

There are 2 bolts at the rear of the intake manifold that must come out. I cannot see any way to remove those bolts with the "bulkhead" in place. Believe me, I've tried.

I am very familiar with the links and posts over at MBWorld. Post #14 by JohnnyC with the photo of the manifold removed...is on a GLK. Post #13 by NickW has a link to a procedure for changing the plugs without removing the manifold....on an SLK. The ML is different due to placement of the engine very far aft in the engine compartment and other interferences to the sides. Regardless, unless someone posts a reasonable means to remove the "Bulkhead" I am going to try to non-removal approach.

I checked with a shop-owner friend of mine, and he said:

“We have done plugs on this engine, and there was no bulkhead removal. However I could understand that would be possible on an M class. There is a reason that we charge either three or four hours of labor to do this job. But I really don’t think you need to take the intake manifold off, I believe once the ECU is off on the driver side and the air filters off on the other side you can get the coils out and get to everything. One key to success is having really good tools and a variety of extension lengths.
it’s not just the ECU but it’s whole bracket comes off. I do remember I had a customer who tried to do his own plugs and had started by trying to take the intake manifold off and I said: “I don’t ever do that...” “

Thanks. That is pretty much what I am hoping. I'm not tackling the job for a few days. I'll update when I do.

Just to close the loop. I did the job. I did not pull the intake manifold because I could not get any advise how the remove the center bulkhead section. This is the worst job I have ever performed on any M-B (since 1963). Removing the intake manifold may have helped but it still would not have been easy. Bottom line – it took me a lot of careful study and experimenting with various tools – and 4 hours on the driver's side and 1.5 hours on the passengers side.

Vince, thanks for doing all the research on this; my wife's 2015 ML is pushing 45k miles, and I've begun research on the project. Every thread I find ends up back at your adventures.
Like you, I really don't want to fight my way through the intake removal and the bulkhead mystery.

Figured I'd change the plugs at 50k, but now may put it off to the full 60k .

Maybe that guy with the injector problem photos will tell us how he popped the middle bulkhead off - but I bet it's a bear also.

Thought the toughest job I would do for awhile would be the rework of the old 300 SE sunroof, but this looks to be MUCH worse.

BTW, I can change the plugs in that old car in five minutes, wearing a white suit!
I guess life averages out over the long haul.

Cheers,
DG