Mercedes-Benz W126 distributor cap, rotor and spark plug wires
W126 runs jerkily or stalls, could the cause be the distributor cap or rotor?
Yes. A cracked cap lets moisture in, and a broken or burnt rotor weakens the spark. Symptoms are rough running, uneven idle, jerking and poor throttle response. The cap and rotor are usually renewed together.
How is the W126 distributor cap removed?
1. Mark the positions of the spark plug wires. 2. Pull the wires off by the boot, not by the wire. 3. Open the cap with a hex key. On the M103 there are three screws (5 mm). 4. Move the wires to the new cap one at a time into the same positions. Do not spray CRC on the cap.
What should be checked on the spark plug wires?
Leakage from a wire shows in the dark as sparking, and the leak is easier to see when the wires are wetted with water. Green corrosion can form at the wire ends and weaken operation. It can be scraped off carefully.
What else is checked if running is still uneven after a new cap and rotor?
Check the spark plugs and plug wires, and the vacuum hoses, which can be split at the connector even though they look intact. An air leak causes similar symptoms.