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1985 500SEL
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835 Posts
Discussion Starter #1
I did full tune up this weekend

(Spark plugs, wires, rotor cap and air filter)
the fuel filter was changed as well..

I used spark plugs W9DC0 (.032 GAP)

the car is idling a little rougher(at idle) and shakes worse than what it use to.. The old plugs were W9DC...

is this the reason?.. I was reading in mercedesshop that some people have same problem. but I got it from this forum that i should use W9DC0

please advice...
 

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Depends on the day!
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Shouldn't be a problem..check and make sure all your wires etc are firmly on.. THey can be a pain sometimes. Did you pull all the wires from the boot? If you pulled on any of the wires there is a very good chance you broke one or two. You can always check them (wires) w/ an ohm meter.

Jonathan
 

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1991 500SEC sub 50K mi. 1987 560SEC Now 150K mi. 2018
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4,292 Posts
Hi Kingorcus,

While reading your post, I was reminded of something I've done a couple of times while changing plug wires. This probably doesn't apply here, but I'm wondering if it is possible that a couple of the leads got mixed up? If so, it could explain the symptoms you describe... [?]

Good luck, MBL
 

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1985 500SEL
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835 Posts
Discussion Starter #4
Update....

I pulled all the plugs out and cleaned them (some had a little much anti-sieze) I regapped all to 0.038

Idle smooth like silk now..

Thanks to all especially Jonathan..

If I was near Atlanta, I would let you fix my car b4 any benz dealer..
 

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1987 420 SEL
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2,090 Posts
When ever you do your tune-up. It's always good to take your time and while things are apart, check all wires and other electrical contact points for corrosion, breaks, etc.

When I did my tune-up about 3 weeks ago, I upgraded my wires from the originals to Beru. As I changed each plug, I changed the corresponding wire and numbered each wire at the top of the distributor and on the end leading to the plug for easy reference then and in the future. I looked over my entire engine bay for about an hour afterwards while the car was running looking for any missing hose, wire, etc. Believe me, it helps a lot. It allows you to become very familiar with what's going on while the car is operating. Then you can point out the different components, especially if you have the vacuum diagram in your hand. Try it, you'll like it!!! [:D]
 

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1991 500SEC sub 50K mi. 1987 560SEC Now 150K mi. 2018
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Hi King,

A lo-o-o-ong time ago, an hour after doing a tuneup on my Volvo 140, the car wouldn't start, cranked fine & wouldn't catch. ??

I'd used Anti-Seize as a cam lubricant for the ignition points. Shorted them right out.

:eek:) MBL
 

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12-Camel TT S600
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and whats the MB recommended spark plug gaps.. did u regapped them differnt from what the manual says??

the MB stated gap is 0.8mm (0.031Inch)

0.038inch = 0.96mm

i have the same problems of rough idle and shaking ..no matter what i did.. cleaned injectors, changed wires, tried bosch W7DC, W8DC and Denso Indium plugs..idle wont smooth up [xx(]
 

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Have you replaced your wires, cap, rotor? Did you check your wire w/ an ohm meter? Did you do a compression test? When you pull the plugs have you inspected them to see which isn't firing well??

Jonathan
 

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1985 500SEL
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Discussion Starter #10
yes the gap should be .032

but Jonathan does his @ 0.042

so I took a mid range .038

some people say it will be smoother to open a gap a bit.. but I am not sure what solved my problem, the bigger gap or cleaning the pluggs..

oh well good luck on your idle
 

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2016 E400 4Matic Sedan
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610 Posts
for your references, I replaced a set of W9DC0 with W9DC for my 560SEL. Per suggestions on this and other DIY boards, I set the gap to 0.040. I have been enjoying a very smooth idle ever since.

Currently, I am getting about 17.5 MPG commuting to work. It is 13 miles one way and mostly stop and go traffic.
 

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12-Camel TT S600
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how do i check vacum lines and stuff.. can someone send a chapter abt this from repair manual to my email... i havent got my repair manual shipped yet..

my caps, rotors, wires, harness, blah blah blah.. everything is new...engines is putting right compression..

i think gradual wear on all the engine components need compensation by increasing the spark gap or so.. anyway are there any sparks plugs pregapped 0.038 or 0.040 which i can use.. what abt bosch platinum+4..will they improve my idle.. the platinum+4 manual says not to regap them ever..

r u feeling any downside of regapping at higher engine rpm.. like slighly lower response or misfire at cold start>??
 

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1987 420 SEL
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Hey theboss. You can locate a lot of information by going into "search" using 'vacuum lines' here on the forum. You'll be surprised how a small disconnected hose can affect your idle. Hope this helps.
 

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1985 500SEL
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Discussion Starter #15
The Boss

from what I can tell, these spark plugs come usualy gapped @ .032

so you need to regap them (easy, get plug gapper from parts store)

and so far.. I don't notice any loss in performance or missfire.. Actually the car response better from b4...
 

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i regapped to 0.040 and idle smoothen down.....woooohoooo.. good time showing off and out-smarting my mechanic.. he couldnt figure out what i did and im not telling him the secret.. just told him he needs to learn more [:p]
 
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