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Spark Plug Replacement An article written and kindly provided by Brett Allison Note that this was written using a 1997 S600 as the subject car. It may or may not apply to other years! This write-up documents changing the plugs in my car, a 1997 S600. 1995 and earlier model years with distributor ignition will not have the ignition coils shown in the pics at each cylinder. (Note...The info in this write-up applies to earlier V12's as well, with the exception of the ignition coils. 95 and earlier do not have coils, the plug wires attach directly to the plugs) Changing the spark plugs in the V12 is pretty straightforward except for cylinder #12, which is buried under the tray for the wiring harnesses. It took me about 45 min to do #12 and another 1 hr to do the other 11. If you’re more creative than I was with flexible extensions and socket universal joints, you may be able to reach #12 without flipping up the wiring harness tray as I am about to describe. #12 is under the tray as shown in this pic. # 6 is also partially blocked, but you can reach it with two shorter extensions and a U-joint.
Begin by removing the climate control intake plenum (same thing you would do to change the pollen filter). First, disconnect the vacuum line to the flap on the passenger side, and then remove 6 screws shown in the pic.
Under the driver’s side of the plenum, twist and release the climate control’s air temp sensor.
And, finally disconnect the electrical connector for the wires to the smog sensor, and lift the intake plenum out of the car.
Now, from the driver’s side flip up the wiring harness tray that is behind the firewall. It is hinged and easily lifts up. Remove the three 8 mm hex screws holding the forward harness tray (the one above #12) in place.
Lift the tray, and you’ll see that you now have easy access to #12. The tray is split in the middle so you can just lift this side of it enough without having to undo the entire tray all the way across the engine compartment.
Change out #12, put the tray back in place, and reinstall the climate control plenum. Then move on to the other 11 plugs. Changing each plug requires removal of the ignition coil. To do this, disconnect the coil’s electrical connector, unclip the metal clip that holds the coil, and grasp the coil by the top and wiggle it out of the spark plug tube. You then need to remove the coil’s retaining clip. Just squeeze the open end of the clip, and work it off of the intake manifold. You’ll see. Here’s the removal of the ignition coil.
I used an air duster can to blow any junk out of the spark plug tube. An air compressor hose would be better. The ignition coils have rubber gaskets to prevent stuff from falling into the tube, but better to be sure. You don’t want any grit falling into the cylinder. Using a spark plug socket on the end of a long extension, remove the old plug and install the new one. Torque the new spark plug to the appropriate value. My owner’s manual said 20-30 Nm. Replace the coil retaining clip and the ignition coil, and reconnect the electrical connector. After 8 are done, it’s kind of annoying to think that the V8 guys are kicking back enjoying a beer by now. Hang in there. I know your back is killing you. Only 4 more to go. When you’re done, check your work. I actually left a coil unconnected and didn’t find it until I had started the car and experienced a shaking engine from the misfire. Re-checking revealed the disconnected coil. UPDATE!
Many Thanks go to Brett for this fine write up! Click here to e-mail Brett
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