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Old 09-12-2002, 11:47 PM
BENZ-LGB's Avatar
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Join Date: Apr 2001
Location: Southern California
Posts: 1,663
Thumbs up Spark plug help

A couple of weeks ago I asked for help in finding a link that had pictures (like the ones found in Chilton and Haynes manuals) of what used spark plugs look like.

The condition of spark plugs is a good diagnostic tool. I no longer own Chilton or Haynes manuals so I wanted to find a handy link with pics of spark plugs.

I finally found a Bosch link (from Australia) with lots of handy information about spark plugs, including pictures. Here is the link:

You need Adobe to view it.

I do have another spark plug many of you use resistor type plugs? And if you do, why do you use them? Any problems?

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1989 300TE "Alice"
1990 300CE "Sam Spade"
1991 300CE "Beowulf" RIP (06.1991 - 10.10.2007)
1998 E320 "Orson"
2002 C320 Wagon "Molly Fox"

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Old 09-13-2002, 12:55 AM
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Join Date: Jul 2002
Location: Dallas
Posts: 330
I had problems with resistor plugs. The auto parts store where I was buying plugs sold me plugs with an "R" in the number, stating they were what the manufacturer listed in their book as the replacement plug for my E320. So I took them and installed, not knowing any better. They ran fine for about 500-800 miles, but then I developed an unusual stumbling at idle. Felt like I was getting bumped in the rear. Replaced the plugs a few times with different brands, all with "R" in the number, with the same outcome. Searched all the BBs I could find and never got anywhere. Had people telling me to replace the OVP relay, MAF sensor, plug wires, ignition coils, ad infinitum.

Finally I had an epiphany after doing like you and researching plugs on the NGK website. I learned that the "R" in the plug number was for resistance. I surmised from kitchen physics in college that the by-product of resistance is heat and that likely thinks were a little too hot down in the old spark plug holes. I also had read about the resistor ends on the spark plug wires that attach to the plugs. With the resistor ends AND the resistor plugs, too much resistance. So I ordered a new set of resistor ends from performance Motorcars (about $70) and went to the dealer, which had THE CORRECT DAMN PLUG as specified in the owner's manual. Installed all in about 30 minutes and to date (about 6 months) no more stumbling idle. Moral of the story - Use the right plug in your car. Forget the platinum, splitfire, resistor, double trouble hoopla and get the good old copper plug specified in the cars literature.
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Old 09-13-2002, 08:06 AM
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Join Date: Sep 2001
Location: Wrightsville Beach NC
Posts: 1,512
Listen to E320 he know what he is talking about. I had the exact same problem as he. I now run bosch super H 8 DC's and everthing is grand

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