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Old 09-12-2002, 11:47 PM
BENZ-LGB's Avatar
Strong, silent type
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?

Current Benzes

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
Registered User
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
drbrandini's Avatar
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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