560 SEL Intermittent Misfire

1979-1991 280SE, 300SE, 300SEL, 380SE, 380SEL, 380SEC, 420SE, 420SEL, 420SEC, 500SE, 500SEL, 500SEC, 560SEL, 560SEC
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Joined: Mon 31 Jul, 2017 11:28 am
Model you own: w126

560 SEL Intermittent Misfire

Post by jaybenz » Mon 31 Jul, 2017 11:30 am

Hello everyone

Over the years I have lost count the amount of times to have made reference to this forum in search of information on the countless amount of new or old Mercs ive owned over the years.

Im currently experiencing an issue with my 560SEL and it doesnt seem I can find anyone else who has experienced a similar problem. I hope reaching out to the community can not only help me to solve this issue but anyone else who may have the same problem as im sure im not the only one to have experienced it.

CAR - 86 560SEL with ECE option (No o2 sensor)

Issue - Intermittent misfire

By misfire I dont mean a the engine has a little stumble every 10 seconds or so, what im talking about here is sometimes the car feels like its running on 5 or 6 cylinders.

This morning for example I started the car it ran very smoothly. I drove it to the shop 3 minutes away, switched off the motor, returned to the car 3-5 minutes later and it was running like only 5 out of 8 pots wanted to work.

After putting in new plugs and checking them after a little rough running I see the plugs are all black, like covered in soot. However after checking them while its running well they are a great color.

My thought are limited I really have no idea where to even start looking. Leads/dist cap/rotor LOOK ok but who knows.... I did notice on weekend if I disconnect a plug lead from distributor while engine running that a spark earths from the electrode to the body of distributor. While running rough and disconnecting leads from distributor it made very little difference to the sound the engine was making.

Also when running smooth if I was to rev it right out it may or may not stutter as revs get higher than 4k.

Also when running smoothly it is down on power. Not heavily but it doesnt quite feel like it is making as much as it should.

Any help appreciated.

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