Symptoms suggesting a bad distributor rotor:
* Engine won't start or runs roughly: This is the most common symptom. A damaged rotor can't reliably distribute the high voltage to the spark plugs, leading to misfires or complete failure to ignite the fuel-air mixture. The misfire might be worse at certain engine speeds.
* Engine misfires: The engine might sputter, hesitate, or run roughly, especially under load or at higher RPMs. This is due to inconsistent spark delivery to one or more cylinders.
* Visible damage to the rotor: Inspect the rotor itself. Look for:
* Cracks: Cracks in the rotor material will disrupt the electrical path.
* Burning or discoloration: Excessive heat from arcing can cause the rotor to burn or discolor. A dark, scorched appearance is a strong indicator.
* Excessive wear: The contact points on the rotor can wear down over time, impacting conductivity.
* Corrosion: Moisture or dirt can cause corrosion, hindering electrical conductivity.
How to check it:
1. Visual inspection: Remove the distributor cap (after disconnecting the negative battery cable!). Carefully inspect the rotor for any of the above-mentioned problems. A flashlight will help.
2. Check for arcing: With the cap off, carefully rotate the engine (with a wrench on the crankshaft) and look closely at the rotor tip and its contact with the cap's terminals. You shouldn't see any sparks jumping across a significant gap. Arcing indicates a problem somewhere in the ignition system, and a worn or damaged rotor is a prime suspect. (Caution: High voltage is present even with the ignition off. Be careful not to touch any components while checking this.)
3. Check the rest of the ignition system: If the rotor looks good, the problem might lie elsewhere in the ignition system (worn spark plugs, bad wires, faulty coil, etc.). A bad rotor is more likely to cause *intermittent* problems, unlike a completely dead coil which will usually prevent starting altogether.
Important Note: Always disconnect the negative battery cable before working on any part of the ignition system to prevent electric shock and accidental short circuits. If you're uncomfortable working on your vehicle's ignition system, it's best to consult a qualified mechanic.
