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Registered 2001 SLK320
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41 Posts
Discussion Starter #1
Nice day yesterday, mid-60's, SLK humming fine. Stopped at last stop light before entrance ramp. Light changes, and of course, I'm behind the slowest person in the world leaving the line. After waiting for the other lanes to clear, I hammer down, get around the moving speed bump, running up to about 90 getting onto the on-ramp and motivating down the highway for maybe 30 seconds, before dropping back down to 70.
At which point the CHECK ENGINE light comes on. It feels relatively okay, and I exit in about 5 miles. At the light, I can tell something is not right. She is idling rough and poor throttle response, almost like she's not getting fuel or a coil pack is dropping out. I limp home a mile away at 30+ MPH and park and shut her down. Under the hood, nothing glaring other than a bit low on oil (she'd due for a change).
I start her back up and she's back purring like before. I run up the street and back, still good. Drive out to dinner and show later, again, good to go.
Only problem now is - stupid light is still on.
A) Any ideas as to what might have happened?
B) How can I turn the light off?
C) I have flexible maintenance, how can I reset the clock for the oil change?
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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96,644 Posts
Welcome to the World’s Premier Mercedes-Benz SLK Community from Valrico, Florida!


Please update your location/vehicle (model and year) in your profile as it helps the members answer your questions which usually are based on that information.
‘Usercp’ at the top left of page, then ‘edit your details’ on the left side, ‘additional information’ near the bottom, edit your ‘location’ and ‘vehicle’.

You might want to post an introduction in the ‘New members introduce yourself here’ section, if you haven’t already.




If you haven’t, please use the 'search' feature at the top of the page for your questions as they have probably been asked before. Remember, ‘Search’ is your friend.
In addition, if you haven’t, please post your question in the appropriate discussion forum for a quicker response. Be patient and a knowledgeable member will address your question.
If you wish to become PM (Private Message)- capable, you need 15 posts. To get those 15 posts quickly, just go to the ‘New members introduce yourself here’ section and welcome enough new members to obtain your needed posts to PM.
New members and guests should be aware that the 'New Posts' link next to the 'Search' link top right of the info bar is a great way to see all of the posts you have missed since you were on the forum last. Remember to click 'mark forums read' under quick links when you leave.
Also vote or enter our Ride of the Month competition: http://www.slkworld.com/rotm-submissions-voting/

Thank you,
Jeff
Moderator/Founding Member
 

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Registered 2001 SLK320
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41 Posts
Discussion Starter #3
intro

Odd - I joined, as you can see, over 2 years ago, having brought over some information I had that I had previously posted on the BENZWORLD forum.
I do see now that my vehicle is not public, so I made that change.
I'm not sure why it does not show my previous posts as it contained the information for both the jack-point "pucks" and the rubber bumper in the trunk that supported the roof when stowed.
At any rate, my appologies if I offended anyone.
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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96,644 Posts
info in garage does not communicate with the info in your profile on left side. sent you pm
 

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Premium Member 2013 SLK250
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2,387 Posts
You need to have the codes read and that will tell you what is the problem. You do not show where you live. If in the US you can go to the big auto parts chains and most will do a reading for you. The codes will tell you what was/is the problem. You might want to reset the codes and see if it comes back. Could be a rare thing that happen and not a problem.
 

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Registered 2001 SLK320
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41 Posts
Discussion Starter #6
Thanks. Jeff explained the issue with the locale and car - fixed!

I'll stop by the zone or other chain and have them pull it. Do they all have the adapter for the Benz or should I call first?
 

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Premium Member
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1,314 Posts
Resetting service indicator and resetting clock info are both in your owners manual and probably on the forum somewhere via a search. Both pretty easy to do.
 

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Registered 2001 SLK320
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41 Posts
Discussion Starter #8
AutoZone pulled the codes and reset the light.
Appears the #4 cylinder dropped out when I was doing my high-speed run. It also said something like it needed a tune up. With 147K miles, it probably has the same plugs and wires. The coil pack on #4 may have dropped out.
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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96,644 Posts
So now you have your game plan!
 

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Premium Member 2013 SLK250
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2,387 Posts
AutoZone pulled the codes and reset the light.
Appears the #4 cylinder dropped out when I was doing my high-speed run. It also said something like it needed a tune up. With 147K miles, it probably has the same plugs and wires. The coil pack on #4 may have dropped out.

They cleared the codes. Time will tell if you have a problem or it was a glich. Sometimes there is a glich and the cars computer will register it and turn on the check engine light and does not happen again. If comes on again very soon than you have a problem that needs repair work. You read the codes again and it is again #4 cylinder dropped then look at the items you mentioned. You could swap the coil pack with another cylinder and see you get a reading that the swapped cylinder was dropped. If so then it is the coil pack if it is still #4 then time for wires and plugs. I hope it was just a glich.
 

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Premium Member 2013 SLK250
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2,387 Posts
Resetting service indicator and resetting clock info are both in your owners manual and probably on the forum somewhere via a search. Both pretty easy to do.

The codes to reset/clear are the ones for the check engine light turned on by the cars computer. You use a ODB2 reader to do this.
 

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Registered 2001 SLK320
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41 Posts
Discussion Starter #12
I ordered plugs and wires since they are over 11 years old with 147K on them.
The code they printed out: P0304 Number 4 misfire detected
This would explain the rough running and idle when I exited. However, from my way of thinking, plugs and wires should not magically start working again after a shutdown. I am more inclined to think it is something more electrically controlled. Unfortunately, the coil pack is not that "technical", it should fire when it gets a signal from the ingnition system/control module - which leads me to be wary of the ECM or ignition module.
We'll get the plugs and wires in and then we'll "wait and see". Since I will probably move the coil pack rail out of the way when doing it, I may follow the advice and swap the #4 coil pack with another on that side just to see if it is a weak link.
 

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20 Posts
It is more likely to be a coil pack than plugs/wires. Coil packs don't stand up to heat very well over time and will develop small fatigue cracks. They will often start to fail intermittently at first and get worse over time.

Although the coil packs are fairly well shrouded on the 320, never hose your engine down when it's hot. Hitting a hot coil pack with cold water will eventually cause it to develop thermal cracks, suck in water and short the coil.

Swapping coil packs with another cylinder (as someone suggested) is a good idea at determining if it's the coil, plug, wiring, etc. On modern engines they don't use plug wires anymore. The coil packs plug directly onto the spark plugs and a low voltage signal is used to fire it so there are no longer any high voltage wires that can break down like on older engines.

Hope this helps,
Rob
 

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11 Posts
Hi there, my check engine light came on also this morning when i push the throttle hard, then immediately i park the car and check. It seem no problem with engine, it response as normal, what i'm worried is the check engine light, i drove 55miles and it's not turning off, i will check later after work if the light still there. my car was R170 SLK230 2002 from US shift here in United Arab Emirates and now it's 66
Degrees Fahrenheit here. Do you think what cause this light to turn on this is the first time. Thank you in advanced.
 

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Registered
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20 Posts
You are fine to drive the car with the CEL on. It only has to do with emissions related faults. You will need to read the fault code with an OBDII reader and report back. There may be more than one. Most auto parts stores will pull the codes for you for free if you don't have access to one.

Rob
 
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