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ML320
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Discussion Starter #1
My ML320 has 97000 miles on it. The dealership guy said to me the car needs a set of new spark plugs. The charge is aorund $500. I am DIY guy, how can I replace the spark plugs? Please help.
 

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'01-E320 & 02-ST2
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31,633 Posts
Hi, Philip.

You absolutely can. Plugs are cheap, just stay with OEM replacements, autohausaz.com has them for a great price with free shipping (you need 12, in case you didn't know, Bosch 7422 @4.37 each). Buy the special wrench/tool to remove the plug wires, SG motorsports on ebay has it for about $26 with shipping IIRC. There is probably a DIY in the 163 forum, else you can reference the one in the 210 forum, same engine/procedures, search and you shall find.

Two caveats: First, treat the ignition wires as if they were eggs, they are pretty fragile and will fail if handled roughly (and they are stunningly expensive). You will NOT be able to remove them without a tool, if you try with your bare hands you will damage the wires.

Second, do not use anti-seize on the plug threads, they are coated for this purpose and anti-seize will destroy your torque readings.

Take care and enjoy the ride,
Greg
 

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2005 E320 CDI, 2007 S550, 2016 E250
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3,199 Posts
FAR...you are my hero.

Gregs...I was wondering where you found info that Bosch was stock? The manual states to replace with NGK...and the box the OEM versions came in from Mercedes had the same NGK part number. Just curious :)

OP...search is your friend - good luck on the DIY.
 

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1973 450 SL AMG, 1999 ml320
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211 Posts
I changed my spark plugs with bosch +2 and they were only 4.00 at my local auto parts store. I needed to get 12 of them. And the cost was a little over 60.00. I get a little better MPG and more HP( ok maybe 10 hp with the k&n air filter)
 

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ML320 2002
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17 Posts
SPark Plug Thread

Hi

I am about to change the spark plugs on my ML320.

I understand there are 12 plugs to change.

Do all the plugs have a normal thread (i.e. clockwise to tighten and anti-clockwise to loosen?

Thanks
 

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2000 ML320
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74 Posts
Yes they are normal thread. Don't be surprised at the amount of torque it takes to remove the plugs, might were tight almost the entire way out.
 

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1998 SL500, 1999 ML320
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634 Posts
I got some great help from this general forum about having a bad crankshaft position sensor and the car not starting or running well when hot. RIGHT ON and thanks.

This may be the wrong thread but I'd like to ask for what I think is related to this thread.

The car (1999 ML320) is having a rough idle, but not enough to show on my simple (but fairly good) scanner. It drives like a champ, the only noise is tire tread noise (can't say that for the '98 SL500). Still doing gentle starts and stops after resetting the transmission (that process actually works).

Now for the question . . . Is there any thing else I can easily check that might cause the rough idle but not affect driving performance?

I have the notion that I can, for about the price of a dealer full-on scan, buy 12 plugs and maybe 6 coils and just replace the whole thing. The car is at about 77,000 miles seems to otherwise be in good shape.

I'm not much concerned about the type of plug, I'll just buy what the manual recommends.

[One in-related question. Someone who looked under the hood with me recently asked where the black plastic engine cover was. I don't remember seeing one, see them in some videos in these groups, but not on the ML. Should it have one and if so, is it for anything other than cosmetics?]
 

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2000 ML55 sold😢 2013 ML500,😁 2015 C250 estate wagon, 1927 Dodge 4 sedan, 1929 Dodge
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4,685 Posts
Bad plugs or leads could cause a rough idle. Coils should be ok. Go with NGK plugs and change them first. Check each plug lead for a greenish corrosion on the connections both ends. That could also cause a rough idle. Give them a good clean if there is and a spray with contact cleaner.
See how it goes from there.
IMG_1888.jpg


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Dallas, Texas
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Someone who looked under the hood with me recently asked where the black plastic engine cover was. I don't remember seeing one, see them in some videos in these groups, but not on the ML. Should it have one and if so, is it for anything other than cosmetics?]
That cover keeps cosmic debris from entering cylinders and messing up ignition pattern.:)

If you want to approach this issue with parts gun you will need 6 coils, 12 spark plugs, 12 ignition wires.:wink
 

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07 W219 CLS 350 CGI (sold), 03 W163 ML 500,
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192 Posts
Now for the question . . . Is there any thing else I can easily check that might cause the rough idle but not affect driving performance?

[One in-related question. Someone who looked under the hood with me recently asked where the black plastic engine cover was. I don't remember seeing one, see them in some videos in these groups, but not on the ML. Should it have one and if so, is it for anything other than cosmetics?]
Hi,

Rough idle can come from:
-undesired air entrance in the intake manifold
-fuel injector leaking
-O2 sensor problem
-unapropiate electrode gap on spark plugs
-etc.
I doubt about engine mounts, you can easily check this by quick releasing gas pedal or just by hand throttle having a look under the hood (engine should just have very small move).

About the black plastic engine cover missing, it is mainly there for cosmétic reasons (and shelter for mice if exterior parking...), no worry about it.
 

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2000 ML320 LHD
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666 Posts
Another problem you should check is the possibility of bad engine mounts causing shakiness at idle.
Hi,

Rough idle can come from:
-undesired air entrance in the intake manifold
-fuel injector leaking
-O2 sensor problem
-unapropiate electrode gap on spark plugs
-etc.
I doubt about engine mounts, you can easily check this by quick releasing gas pedal or just by hand throttle having a look under the hood (engine should just have very small move).

About the black plastic engine cover missing, it is mainly there for cosmétic reasons (and shelter for mice if exterior parking...), no worry about it.
Oldwineuser, bad engine mount is also a possibility as I've had an experience with it.
 

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1999 ML320
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91 Posts
I just replaced my spark plugs and ignition wires today. :yelrotflmao:
A 17mm open wrench is a must to pull the boots. There's a bent version of the wrench that makes things easier, but with some ability and patience you can use a regular wrench as well.
The access is easier if you remove the coils.

Two of the wires were almost dead, due to corrosion. As I had a complete set sitting around I changed them all, and keep the old ones that still good as spare.

It's supposed to be a half day job. I took some more time because I also resealed a leaky breater's cover.
I've found that some lousy mechanic damaged the border where the cover sits, probably hammered a screwdriver in there to remove the cover. :mad:
That's why the leak reappeared. Took me a couple of hours to repair it properly.

The spark plugs were terrible after more than 100k miles, and I noticed that they were the wrong type, a colder type, so they had many deposits on the electrodes.
Such plugs were so bad that I do expect a great improvement on the consumption. :thumbsup:
Let's see.
Now... a deserved beer! :beerchugr:
 
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