I have a 98 ML320 that's due for a plug change(150000km of short city driving). What steps are involved? I notice there are metal covers over the plug ends and a star shape section 2-3 inches out from the ends. Can someone tell me how the metal ends are removed to access the spark plug boot end. A while ago, I think Gilly or someone mentioned that there was some sort of 17mm device needed to do this job. If so, what's the name of this tool and where can I buy one. Any info is appreciated.

Tks,
VLowe

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Vern Lowe

The metal ends are part of the wire, they are NOT removed independently of the wires.
There is a 17mm wrench that was originally to be used to adjust valves on the inline 6 M110 motor. THAT is what MB recommends be used to remove the plug wires from the plugs. I believe it is tool # 110-589-01-01-00. Here is a place that seems to have it for sale for about $50-$60:
http://www.samstagsales.com/mercedes.htm
You may be able to get them off using a spark plug wire pullung pliers, but this 17mm wrench has a really nice bend to it that makes it lever off the ends really nice.
The open end part of the wrench goes onto the narrow part of the metal end and then the wrench is pried against the valve cover to wedge off the wire ends. I recommend also removing the coils from the valve covers to do this job.
You will want to remove the engine cover to do this job, I usually remove the air cleaner box also to get better access to the right bank.
You are actually overdue for this job by quite a bit, as the plugs also have a time expiration of 4 years on a 1998.

Gilly

Tks for the information Gilly. I'll be doing it on the weekend.

Vern

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Vern Lowe

My dealer Holloway Motors ordered this valve adjustment tool (for sparkplug wire removal) for me for $26.50. I found access to the plugs was a lot better by removing the tire and inner fender liner as others have suggested.

Gilly,

Changed the plugs in my ML today. You're right, based on the gap of the old plugs(.045-.048" vs .032" spec), they probably should have been changed at 80-90,000Km although the Cdn manual says 160,000Km with no mention of the 4 yrs. Temp. range looked good based on the tan colour of the insulator. ML should idle smoother now and be a bit peppier.

Couldn't wait for the tool so found that an offset flare nut wrench worked not bad for pulling off wires.

Just a note to other owners. Original plugs were Bosch F8DPER, single gnd. Local parts stores say Bosch has replaced these with the 4301, dual gnd electrodes. both are still Platinum.

Tks,
Vern

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Vern Lowe

Isn't it riduculous what has to be done to R&R spark plugs. The engineers should have to serve as mechanics for 5 years before they design the engines and maybe they would make them more serviceable.

Fat chance they will ever sell me anything that its a major repair to replace the spark plugs. I'll stick with my old Diesels.

P E H

Honda spark plugs are right on the top, of the engine, You can probably change the plugs in 10 mins tops.. But I think Mercedes might have put the plugs on the bottom so when owners open the hood, they see a very clean engine with less wires.. Afterall they do charge $100 hour for the extra work =)