Mercedes-Benz W140 distributor cap and rotor
420500 S400 SES 300SEL 400400 SEL
Why does the W140 misfire or cylinders drop out because of the distributor?
The distributor cap and rotor can oxidize or crack, leaving a burnt trace between the terminals. The result is misfiring, an uneven idle or cylinders that go dead, especially once the engine has warmed up.
Is cleaning the distributor cap and rotor enough?
Cleaning can help for a while, but often it is not enough, and the fault can return or get worse. The sure repair is replacing the cap and rotor. Replacing just the rotor has also given only a temporary improvement.
Should the distributor cap and rotor be replaced together?
Yes. Old and new parts do not work best together, so the cap and rotor should be replaced at the same time. At the same time, replace the O-ring under the cap, which hardens and lets moisture through.
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