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  #1  
Old 11-18-2002, 02:46 PM
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Changing Spark Plugs on M119

Car:1999 S420 48,000 MILES, time to change sparks
Alright, I got the air filter housing off and now I see two black covers on each valve cover with funky screws. I need directions on how to remove the cover and how to change the spark plugs. By the way, I've never changed spark plugs before. I'll be buying the sparks from Fastlane. Do I have to gap the spark plugs? The 99 S420, is a distributorless ignition.
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  #2  
Old 11-18-2002, 08:59 PM
Gary Ganaway's Avatar
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If its like my 95 E420 I believe there are 2 plastic screws on each black cover. Just unscrew and lift off cover. You might want to invest in a ignition wire puller. Its a plier like tool with plastic protective ends that assist in pulling off the wires from the spark plugs without damaging the connectors. Then use spark plug socket with protective foam or rubber insert to unscrew plugs. You will probably need extension on socket to assist reaching the plugs. My plugs were Bosch, purchased from FASTLANE and I did check the gap but they were already gapped correctly to my car's plug specs

Carefully screw in new plugs to avoid cross threading( you should be able to tell by feel if they are threading properly. I usually start them by hand turning then go to rachet handle to finish tightening. Probably should have torque wrench too, to tighten to proper torque spec. ( I have done this but most of the time I do not...I always seem to have troble with the torque wrench...feels like I have to tighten too much to get wrench to "click"and I am always afraid of over tightening.

I believe some suggest using an anti seize on the plugs...I never have but yes, sometimes getting the old plugs out takes some effort with the socket wrench.

At same time I changed plugs I did new distributor caps and rotors but I was at my 60K service interval.

I'm sure others better qualified than me will have other suggestions and tips. Good Luck
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85 380SE(125k)
95 SL500(72k)
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Old 11-18-2002, 10:16 PM
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Good description, Gary!

The only thing I'd add, from watching my tech do it, is if possible use some compressed air to blow out the well before removing the plug, since the wells are very deep and you don't want that debris to go into the cylinder.
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  #4  
Old 11-18-2002, 10:33 PM
Bud
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Bosch plugs are generally coated with an anti-sieze coating. They are usually gapped correctly also but it's good to check to make sure.

Getting the pliers is a good idea but they are expensive. In any case, be careful removing the plug wire so that you will not damage them. I had all kinds of trouble until I started spraying the inside of the plug wire boot with HD silicon and now they come off with little effort.

I'd also recommend going to Sears and getting an inexpensive torque wrench (about $20). These cheap ones aren't as convenient as the better ones but they work fine for things like plugs.
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  #5  
Old 11-18-2002, 11:42 PM
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The S420 is equipped with the distributor-less M119; there are no spark plug wires. The vehicle uses a coil-over-plug setup. Plug wire puller is not required.
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  #6  
Old 11-19-2002, 12:04 AM
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That's what I thought. Does anyone know how to handle the distributor-less system.
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  #7  
Old 11-19-2002, 10:06 AM
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sorry Royaii, I missed the point about distributor-less M119.
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95 E420 ( 76K) SOLD
85 380SE(125k)
95 SL500(72k)
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  #8  
Old 11-19-2002, 09:49 PM
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Each ignition coil is held in place by a bracket secured by two allen screws(5mm). Remove the screws, set the bracket aside, and pull the coil straight out(it will come out with the suppressor attached). Continue as Gary said previously, and you'll be home free in no time at all. Have fun!
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