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  #1  
Old 08-16-2003, 01:09 PM
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Spark Plug Replacement: ML 320

I found most of the answers to my questions when I used the search for this topic but I still have a few.

1-When changing the left (driver's side) plugs is it necessary to remove the fender liner to access them and use the 17mm Hazet wrench to remove the boots?

2-If you take the coils off do you do that first and do you do that to be able to use the wrench more easily against the valve cover?

3-If you take the coils off will it then be not be necessary to remove the fender liner?

4-When removing the coils are there any special precautions that need to be taken to avoid damaging them? (If never dealt with cars without distributors)

5-What is the torque specification for the fasteners that hold the coils in place?

thanks, ron
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Old 08-16-2003, 04:40 PM
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Ron,

I didn't remove the fender liner but it may be easier to access the plug wires. The coil is held by the one Torx T30 bolt. Just be sure you know which wires goes to which plug(a or B). It helps to rotate the wire slightlyout of the way to pry it off.

I just snugged the Torx bolts up relative to how tight they were when I removed them although I'm sure there is a spec, probably in the 8-10 ft-lb range.

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Old 08-16-2003, 05:14 PM
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Hi Ron

1a: No, I've never removed a fender liner to replace plugs on an ML
1b:No, I don't think you'd NEED the Hazet wrench, it just makes it nicer for getting the plug wire metal ends disconnected from the plugs. You can try any open end 17mm wrench, but the Hazet wrench has an ideal offset to do the job.
2:Remove coils first, I do one bank at a time. There are diagrams on the coils to help make sure you reinstall the wires correctly. The "top" coil wire goes to the "front" spark plug. The reason I do it is to get the plug wires out of the way, and yes it may make the wires easier to get off the plugs. I'd rather not disconnect the wires from the coil, maybe you can try doing it that way instead.
3:No, as I said I've never seen the need to remove the fender liner.
4: YES, don't damage them
I usually disconnect the primary wiring (the single snap on connector) and set them aside. The rear one on the left and front one on the right have a nylon wire tie connecting the harness to it, if you want to snip the wire tie and then replace it when your done that's what I normally do, or if you want to just leave those connected you can do that too, it's YOUR truck!
5: never felt the need to torque those. Just reinstall them as tight as they were before:p

Gilly
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Old 08-16-2003, 07:29 PM
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Gilly and vlowe,

First, thanks for the help.

Since the job seemed pretty easy I figured I'd go ahead and start. I do have the Hazet and it makes getting the spark plug wires off very easy except for the one closest to the firewall on the drivers side, cylinder 6. Anyway I did remove the coils, labelled them to be sure I put them back right. With the coils removed there is plenty of room to get the boots off from above. The 6th plug boot is still in place and I could use some more advise on how to remove it. I tried a regular 17mm wrench but to no avail. The Hazet is to long for me to get it in there; I could cut it but I want to sell it on Ebay when I'm done so I hesitate to do that.

I must say my plugs are extremely tight. I was almost afraid to loosen them, it seemed like it took so much torque to loosen them that they would break althought that has not happened yet. I tighten the ones I replaced to 28nm which is the same torque for the plugs on another German car I have which also has aluminum heads.

Again any hint for that boot closest to the firewall? I'll work on that tommorrow as well as the passenger side plugs.


Edited:
Well I solved my problem as to plug boot 6. I used a piece of wood, 2 1/2" long x 1 1/4 wide x1 1/4 high and placed it on the exhaust manifold and used it as a fulcrum to pry the boot loose with a regular 17mm wrench.

Edited again:

Here's a photo of the high tech device I used as a fulcrum.

Last edited by Ron in SC; 08-16-2003 at 11:34 PM.
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Old 08-16-2003, 10:27 PM
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Well, you did better than I do, i would just carefully pull on the wire and haven't had an "incident" yet. I shoulda warned ya about that one, it is tough.
28nm is correct on the torque. Good job!

Gilly

ps You can actually put those coils on any "hole", but I'm kinda anal about that too, going to great mental lengths to make sure Iput them where they were. Just make sure the wires go back on correctly (that whole a-b thing)
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Old 08-17-2003, 10:00 AM
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Thanks for all the help. Just replaced all the plugs on the passengers side. Everythings back together and works fine.

The gap on the plugs I took out is 1.5mm. The gap on the ones I put is is 1mm. My vehicle has 79,347 miles on it.

I bought my plugs from a Mercedes dealer. The box they came in said the gap is 1mm. and indicate they should be torque to 25nm; I did 28nm.
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Old 08-17-2003, 10:21 AM
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I would always pressure wash the crud off of that engine trim plate when I had it off to do the plugs as well. This was on customer cars of course, who typically don't take care of stuff all that well, like cleaning off the engine anyways. Your's may already be clean.

Gilly
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Old 08-17-2003, 10:59 AM
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Gilly,

Actually I do pressure wash my engine pretty regularly. Which got me to thinking. The spark plugs I removed were way tighter than they should have been. I wonder if all my engine washing may be to much of a good thing being bad. Maybe all that washing caused the plugs to corode enough to make them very tight.

Below is a photo two of the plugs I removed. Do they look like the ones you remove or do they seem to have more corrosion than they should?



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Old 08-17-2003, 11:12 AM
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I tried posting a short time ago, I must have clicked the wrong icon:

Yes, they look fairly normal, especially the threads on the plugs.
They look a little different because they've been in for quite awhile.

When washing the engine, i'd plan on a nice long drive right after doing it, or blow some compressed air around the plug holes.

Gilly
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Old 01-28-2004, 10:07 PM
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Gilly, Thanls for such a quick response. I ll try everything except the fuel filter. The new filter and hoses would be best done with experience.
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