'88 560sl
Installed new copper core spark plugs yesterday because I was unhappy with platinum. Drove 25 miles with no problems, parked for 8 hours. Then she started fine, drove for about 5 miles, Engine lost power dramaticly and was barely running then the muffler hit the ground.

The tail pipe and rear muffler were near white hot and changed color from the heat. All the rubber hanger had melted away.

Temporarily hung the muffler with wire to get it off the road. Noticed that the pipes were hot enough in just 4 minutes that the welds of the muffler were glowing red.

Suspect bad catalytic converter and plan to pull the oxy sensor.

Any opinions??

Sounds like a tune up gone bad. The exhaust will do as you described when raw unburned fuel is dumped through the engine. How is the engine running after the plug change?

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95 E320 Cabriolet, 159K

You are running way over rich. Could be plug wire/secondary igntion failure or a blown diaghram in the fuel distributor.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks for the responses.

Found four bad Plug wires.

Odd failure. I don't think I stressed the wires when changing the plugs. Failure is inside the spark plug boot connector. Some odd electrical stressing related to firing platinum plugs then switching back to copper maybe. Or could just be plain bad luck.

The spark wire terminal at the plug is easily damaged during spark plug service. There's a special tool - when used properly - that removes the boot by pulling on the boot right over the terminal clip. It also helps to coat the inside of the boot with a thin layer of silicone (dielectric) grease to facilitate future spark plug service.

Considering the improvements in automotive design over the decades, spark wire terminals one design weakness that should be addressed by the manufacturers. We shouldn't have to deal with this type of problem anymore.

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95 E320 Cabriolet, 159K

The heat must have come from the cat.

The boots on the plug wires would probably last forever if we didn't change plugs.

I messed up a couple of wires trying to get them off plugs and had to replaced them. Now I spray the inside of the boot with HD silicon spray and they come off easily when I change plugs.

I never had an overheated exhaust system but I did notice an improvement in gas mileage after installing a new set of plug wires.