I have a '98 MB ML320, purchased new, has 94k miles. All maintenance thru approx. 70k miles was performed by Mercedes dealer where vehicle was purchased. I have done all mx. since, primarily oil and filter changes and new brake pads front and rear. Getting close to 100k mile I want to change the plugs. I need guidance on how to get the plug wires off the plugs . I know this sounds stupid but there in a metal sleeve around the plug wire where it attaches to the plug and it baffles me how to get it off so I can remove the plug/s. Another concern arose as I was reading a forum about ml tune ups, is the fact that my plugs may be frozen as they were not changed on or about 4 years after purchase. In checking the mx schedule for the vehicle the plugs should have been changed by the dealer when vehicle was in for a B type maintenance 4 years after purchase. Checking my maintenance file this was not done, nor was I aware it should have been done because of the dealer claim that vechicle did not need a plug change until reaching approx. 100k miles. At any rate the vehicle is almost 8 years old and it is due for a plug change. Vehicle is running fine, no complaints there and gas mileage is according to specs, 19 city, 21/23 highway. So bottom line I want to try a plug change myself, just need some help on a procedure. If I cant remove the plugs because they are frozen it will be off to the dealer. Maybe they will acknowledge that they should have been changed at the 4 year B mx. and give me a break. Yeah, right. Looking for all the help I can get from you Benz Mechs. out there. Thanks, thanks, thanks.

Firstly, spark plugs on your ML320 should be changed every 90-110,000 kms (55-70,000 miles) or every 4 years, which ever occurs first.
To replace spark plugs you will need to remove air filter housing assembly, all coil packs x 6 and all leads x 12, just make sure you mark/note each coil and lead position.

Removing the leads from the spark plugs is the hardest task, holding the lead end (metal part) twist or rotate at the same time pulling hard, whatever you do don't pull on the lead!!
Their will probably be a lot of sweat, blood and maybe tears happening at this stage, oh, and usually a lot of swearing/cursing, so make sure there's no minors around.

Just take your time and be prepared to spend a few hours performing this task.

100,000 miles that the dealer said is correct, but Ramrod is "the most rightest", 4 years also, whichever comes first. It was changed later, with no mods to the engine at all, to 5 years. I don't think there will be a problem, but I'm an optimist at times.
There is a tool "of sorts" recommended by MB to removed the plug boots. It is difficult to use on the last couple wires on the drivers side. It is a wrench with a few curves in it which was originally designed for I believe adjusting valves on the M110 engine. Just to give you an idea of how you do this is that the business end of the wrench (the "flats") slip into the groove you see out towards the outer end of the metal shield. The wrench I think is 17mm, fits quite nicely in that grove. And due to the curving or "drop" of the wrench, you can then pry on it against the valve cover and it levers the plug wire ends off quite nicely, except like I said the rear cylinder on the drivers side, especially the "way back" one. I agree it helps to remove the air cleaner box, yo could even remove the mass airflow sensor, but that's as far as I'd go, not the hard plastic tube, to apt to break the tabs off.

Gilly

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Ramrod, here is a link to a thread about the subject:

http://www.peachparts.com/shopforum/showthread.php?t=71123&highlight=spark+plug+tool

Gilly

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Thanks to Ozzie and Gilly. You were very helpful. I think I will opt for the tool before I attempt the tune up. Ramrod

I pulled all the wires on my ML without removing anything other than the engine cover. You can use a standard 17mm wrench for a few of them, but if you have a pair of mechanic's gloves, you can do the rest by hand. It's not hard at all. Give a little twist and pry. The gloves protect you from the inevitable intantaneous acceleration that your hand will do prior to smacking into the nearest pointy thing.

You do NOT need to remove the coil packs. I do recommend using an OHM Meter to test the wires while you have them off. I believe 2.2k is stamped on each metal boot end. If they are off by much, I would replace the individual wire. The entire set it very expensive, as are the entire set of plugs. By replacing bad wires now, you protect against damage to the coil packs down the road.

I did the entire job in less than 1 hour on my 98 ML320. As previously suggested, removing the air filter box makes it easier to get to the plugs for sure. I bought a K-D Tool spark plug wire puller pliers at O'Reilly Auto Parts for $14.00 and it made easy work of the removing the wires. Be sure to use the pliers on the metal portion of the leads ONLY, and use a twisting motion. The plugs were the original plugs in mine, but I had no problem with seizing. My best recommendation is to remove and replace the plugs only when the engine is dead COLD. That is an old piece of sage wisdom from the advent of aluminum heads, and applies on your all-aluminum M112. Labeling the coils and wires isn't necessary, but would be useful if you find a plug whose condition differs from the others, and want to further test the wires and or/coil. If you have a multi-meter, it wouldn't hurt to test the wires resistance (they should be 2Kohm per the marking on the leads).