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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53015
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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1998 mercedes 300sel: wont start..running fine..starter cranks fine

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My 1998 mercedes 300sel won't start. It was running fine the, the other morning - nothing. The starter cranks fine and although the engine caught for a second, it died right away. It seems as if there is no spark getting to the plugs. There is a switch under the hood up near the drivers side labeled I/O that when turned to O does not allow the engine to start - the bracket is broken but the switch seems to be intact. When I had a starting problem before, by switching this to O and back to I the car did start. This time there seems to be more to it this time.

Hi Brett, I assume you mean the 91 300SEL as in your previous question not a 98. The I/O is not a switch that is a mechanical device to lift the relay up out of the connector. You need to remove that relay and turn the knob so that the metal bracket on the relay pulls up out of the way and then push the relay back down into the connector and see if the car starts. Let me know how you make out.
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