coolram62,

I'm not going to try to start another spark plug debate. I want to just give you my experience with spark plugs in my 84 500SEL. I know it is a different car but the engine is basically the same as yours.

I have tried Bosch WR8DCs and had an idle misfire. I tried platinum plugs. Same idle misfire. Over several years I tried other plugs and had the same problem. I couldn't find W8DC plugs so I tried NGK BP5ES. Idle misfire went away.

A Champion rep came in the shop and ask what kind if spark plugs we used. I said, "What ever the manufacturer calls for if possible." Of course he didn't like that answer. To make a long story shorter, he offered to give me a set of Champion plugs for my 500 free of charge. If I didn't like them he would pay the labor to change them back to what I had in it at the time (BP5ES). I took him up on it. The next day he came back with a set of plugs (I don't remember the number, but they were resistor plugs). I had him get in the car, I set the brake, started the engine, put it in drive, and we sit there and talked for a little bit. Car was so smooth that he kept looking at the tach to see if it was still running.

Changed to his champion plugs as he watched. Same test as above. Engine had a random misfire. At first he didn't say anything but I could tell he wasn't happy.

Changed back to the NGK plugs we had taken out. Test again and all was back to normal. He paid us our regular book rate for changing the plugs two times and said he would be back after he had engineering check the plugs we put in to see if one was defective. I never heard from him again.

So, I just recommend you use Bosch W8DC if you can find them or NGK BP5ES which are still listed and in stock at Advance Auto. Don't get what Advance Auto says is the correct plug for your car. Just ask for the NGK plugs.

They are NON resistor plugs, have not caused any computer problems in my car, they work, and only cost $2.19 ea at Advance.

This is my opinion, and my experiences. Take it for what it is worth.

PaulM

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84 500 SEL (307,xxx miles)