Plugs-SLK200 (R170) - PeachParts Mercedes-Benz Forum

#1 11-05-2003, 07:13 AM

May be this is a very trivial question but.....
I have been searching this great forum, but still I have the following question:
What are the best spark plugs for a 97’ SLK200?

mbdoc · #2 11-05-2003, 12:51 PM

Kompressor or non-compressor motor??

Kompressor engines use BOSCH F7 KTCR plugs

Non-compressor engines use BOSCH F8 DC4 plugs

#3 11-06-2003, 05:20 AM

Thanks MB.DOC. My SLK has a non-compressor engine.
I asked my mechanic after Your replay and he confirmed that the Bosch spark plug type F8DC4 has been used.

Regarding spark plugs, are there any other alternatives for the SLK200 non-compressor engine?
I am asking because lately I have experienced engine misfire.
My SLK works great when cold but at operational temperature the engine hesitates a little bit and misfires under load. The misfire region is from idle (500-700 rpm) to ~2000 rpm. Above 2000 rpm the engine is working well. If I accelerate “carefully” the engine do not misfire but a short hesitation could be felt initially. After a deceleration to below 2000 rpm followed by a fast throttle action the misfire is accentuated.
The air flow meter, O2-sensor (Lambda), both coils and the spark plugs have been replaced. No error codes has been seen.
The strange thing about this misfire problem is that with new spark plugs (F8DC4) the engine was working very well for a short period of time (five days).
Then coil no. two was replaced, still using the “old” spark plugs. The coil change did not cure the misfire but some improvement was observed.
The throttlehouse has been cleaned. Redex (injector cleaner) and STP (Complete Fuel System Cleaner) has been added to the gas with no effect.
Could a defect or poor coil damage the spark plugs? If so I will replace the “old” ones with the same type or do I have some other options….?

In advance, thanks to all that cares to answer. I have read a lot about misfire in this great forum but it is difficult to find cases that “exactly” match my problem and as a consequence (with my knowledge) to find the correct solution.

mbdoc · #4 11-06-2003, 08:22 AM

The Bosch F8 DC4 should be the BEST plug for that engine. If you are fouling the plugs due to fuel OR coil problems, that problem will kill any spark plug.

#5 12-16-2003, 12:53 PM

Thanks to M.B.DOC.
The spark plug tip from you (F8 DC4) resulted in a fully operational SLK200 (non-compressor engine).
It is hard to imaging that the spark plugs could cause so many problems, like rough idle (fluctuations), reduced acceleration/engine power (hesitation) and misfire under load. The fix for these symptoms could have been really expensive.
As learned from this forum the F8 DC4 plugs were gapped to 1.0 mm. The standard gap that is stated in the Bosch manual is 0.8 mm.
The “new” gapping of the plugs resulted in a better (more stable) idle, better cold start, better acceleration (no hesitation). The misfire under load is also history.
The power of the engine at low rpm’s (in the beginning of accel.) is also, without doubt, increased. The engine is smooth and responsible and the car is again a pleasure to drive.
The learning for me is the following: “Do the cheap and easy things first - then the expensive ones”. I have seen this phrase several times in the forum and in my case it was valid.
…and again thank you for this great forum.

maxxie · #6 01-09-2004, 01:27 PM

My God, the SLK owner has had exactly the same problem as I have for e few months now !!!!
My CLK has been converted on Liquid Propan Gas, that is, I can run it on Gas but also on petrol. I will not describe the symptons again, they are the EXACTLY the same as above, running ok for a few days and then degrading again included !! When it misfires with me it sometimes bangs in the exhaust system. Additional facts are: 1) Misfires when running on LPG and petrol. 2) Can't be the HFM, because HFM is not functional when running on LPG but still it misfires. 3) Spark plugs and wires have been replace, running like never before but only for a week or so. 4) Just todayI ordered a new coil to see if that would help. From this post I take I should replace the spark plugs too ????
Do you have any other suggestions ??? You have to know MB dealers, including the one I bought the car new with, are acting very strange, because the car has this LPG installation. It's not an original MB anymore, you see (their point of view). The care never did run very smooth (275.000 km in 4,5 years) but a few weeks ago with the new plugs it felt better than new, was running better on LPG than on petrol in the past. I WISH I FOUND THIS PLACE EARLIER. Thanks for any comments.
Greetings from Belgium
Nico