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1995 SL320
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113 Posts
Discussion Starter #1 (Edited)
My 1995 SL320 runs fine and it has no problem. Another day my Indy told me that those ignition coils ( I have 3 for my L6) will worn out slowly over time, since my car is already 15 years old and I do not know if the last owner(s) had it changed or not, I better change it anyway. (I can buy it here for USD35 each new, Bosch made. I can have those changed DIY in 30 mins because I had experience changing those plugs last month)

I am wondering if I will gain any noticable advantage by doing so? Do they need to be replaced periodically like plugs? Or should I stay with the "don't fix unless it breaks" rule?
Any way I can test/measure those coils and check if they are in good condition?

Thanks for any advices in advance.
 

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Outstanding Contributor
1997 SL600 Brilliant Silver Sport with grey/dark metal interior, 234K miles
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1,977 Posts
There is nothing to be gained by replacing perfectly good seasoned parts.

Wear items like filters and consumables, sure, but not correctly functioning components.
 

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SL55, 300SE, GL450, Daytona 955i
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10,293 Posts
a coil for the most part is good or dead, you will know when one coil is offensing, the car will run as rough as a tank, will misfire, and probably throw a code of the particular misfiring cylender...

bad coils do not rob power without noticable lack of smoothness... so you will feel and know when there is something wrong...
 

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97SL500R129, 01ML320W163, 94E320W124 & 93500EW124
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, the car will run as rough as a tank, will misfire, and probably throw a code of the particular misfiring cylender...
This is absolutely correct. It happened to my 97 and my Indy hooked it to SDS and identified which coils were malfunctioning. We replaced 2 coils out of 8.
 

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1995 SL320
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113 Posts
Discussion Starter #7
Great, thanks for all advices. In this case, I just save the money and buy some Christmas gift for my wife. Cheers.
 

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5,344 Posts
And there's no reason to hook it up to an SDS at a shop. Any old OBDII code reader will read the misfires - codes 300 to 306. And even then there's a chance it's the connector beneath the coil and not the coil itself.
 

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1999 SL500, 2004 CLK500, 2006 Cadillac SRX
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873 Posts
Kevin, I agree with the advice you've been given and your thought to save your money for your wife for Christmas - but, for your piece of mind try this - at night, open your hood, locate the coils, start your car, turn off all lights and look at your coils for any sign of blue spark - arcing. I had a VR4 6 cylinder that had 3 coils (coil pack) and saw the arcing. One of the three was arcing from the coil to the engine block. The symptom of that problem was the car would feel like it was missing intermittently when cruising down the freeway - cruise control on, at 2K to 2.5K RPM. If you do not feel any miss at any time and do not see any arcing, no worries!
 

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SL55, 300SE, GL450, Daytona 955i
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And there's no reason to hook it up to an SDS at a shop. Any old OBDII code reader will read the misfires - codes 300 to 306. And even then there's a chance it's the connector beneath the coil and not the coil itself.
This is correct. misfire codes, and any codes that indicate incomplete burn, or exccessive emmition, are generic codes, that generic scanner should discover on any car. In addition, they will cause the service engine soon light to turn on.
 

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Departed 1998 SL500 (and the Pano is in Bogota)
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All cars sold in the USA since 1996 are required to have OBD-II, but I think MB was ahead of the game. Older models may not have the OBD-II connector (near the steering column) but all the functions were available from the MB's own diagnostic ports. They just re-routed those generic signals to the OBD-II connector when that became mandatory by 1996.
 

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SL320s were partially OBDII compliant in 1994 and fully compliant in 1995. 1995 is an especially good year because you still get OBDI flash code reading on the 38 pin.
 

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1995 SL320
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113 Posts
Discussion Starter #17
Just want to let you know that I finally had those ignition coils changed anyway. The engine now runs even more quietier and smoother like a new japanese car.
 
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