hi.. i have a 1993 mercedes 300se 6cyl and the engine is missing an shaking my question is. how can i tell if it has a bad spark plug wire or a stuck valve i change the plugs i had some in the garage i want to check it myself before i take it to the shop thanks for the help.

You can read the fault codes on the 38 pin diagnostic connector, in particular pins 4, 17 and 19.

You can also check the wires with an ohm meter.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

I don't think that car has 3 coils, i.e. 104.990.

Good correction.

140 chassis 104...no DIS/.992

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A Dalton