Many older vehicles use distributor type ignitions, and the distributor cap and distributor rotor are necessary maintenance items for keeping the engine running smoothly.
How does the ignition cap and rotor work?
The distributor rotor receives the high voltage electricity from the ignition coil, and sends through the distributor through an electrode on the tip of the rotor. As the rotor spins, electrical power is transferred from the rotor to individual electrodes inside the distributor cap. This action is timed for the moment the cylinder needs the spark plug to fire, and the sequence creates a combustion event inside the engine.
What are the symptoms related to a bad ignition cap and rotor?
A failing ignition cap on rotor will create misfires in the engine, and lead to hesitation, extreme power loss, engine stalling, poor fuel mileage, and illumination of the check engine light. The on-board diagnostics (OBD) trouble codes stored in the vehicle's computer will reflect engine misfires, catalyst inefficiency, and O2 sensor related errors. Under the hood there may be audible arching, that sounds like a rubber band snapping, coming from the ignition coil, distributor, or spark plug ends of any of the spark plug wires. Lastly, the ignition distributor cap and rotor may look burned, wet, corroded, or covered in a powder residue, and the spark plug wires may be cracked or degraded.
Can I drive with a ignition cap and rotor problem?
Ignition system components cause many problems when they fail, normally making the vehicle unpleasant or impossible to drive. Also, the amount of unburned fuel going into the catalyst could cause the catalyst to fail, requiring replacement. With severe ignition problems, the vehicle should be towed to a repair facility.
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How often do ignition cap and rotors need to be replaced?
The ignition distributor cap and rotor are both maintenance items, and the replacement schedule is listed in the owner's manual. If the distributor cap and rotor wear out before the specified mileage, they must be replaced early. Some vehicles have issues with distributor leaks, spreading oil onto the distributor rotor and distributor cap, causing misfires. When this occurs, the cap and rotor should be replaced.
How are ignition cap and rotor issues diagnosed?
Diagnosing any of the symptoms mentioned, for a distributor type ignition system, will normally being by checking all ignition components for abnormal conditions that may be indicative of failure. If nothing is found, the spark plug wires, distributor cap and rotor, and spark plugs, more or less in that order, will be removed, inspected, and diagnosed. If the spark plug wires are too resistant to electricity, the spark plugs are worn or fouled, or the distributor and rotor are worn, corroded, or oil fouled, those components would be diagnosed as faulty.
How is a ignition cap and rotor replaced?
If the distributor cap and rotor will be replaced, the spark plug wires will be replaced as well, unless they have been changed according to scheduled maintenance intervals, or they appear to have service life remaining. Likewise, and with the same exceptions, if the spark plug wires are being changed, the distributor and rotor will be changed. The spark plug wires will be marked for their location, and the new spark plug wires will be assembled with the spark plugs and ignition distributor cap using those markings. After the ignition distributor rotor is popped into place, the distributor cap will be installed, and the spark plug wires attached to mounting hardware.
RepairPal Recommendations for ignition cap and rotor issues
If completing this job as a DIY repair, mark the spark plug wires according to which position they sit on the distributor, and to which cylinder they supply power. When having these items changes at a repair facility, ask what type of parts are being used, if they conform to OEM standards, and specify if you prefer to use parts from the manufacturer.
What to look out for when dealing with ignition cap and rotor issues
Some ignition distributor cap and rotors are better than others at getting high voltage current to the spark plug wires efficiently. Purchasing ignition parts that are built to exact OEM standards or better is recommended. Purchasing inferior parts may lead to a repeated repair.
Can I replace the ignition cap and rotor myself?
This is a great task to select as a DIY job. It is an easy repair as long as you take your time, and put all of the spark plug wires in the correct place before removing the old spark plug wires. It is cheap and easy on most vehicles, and in the event you would rather not do it yourself, most shops would not charge a full hour for the labor.
BMW Distributor Cap Replacement Cost Estimates
The average cost for a Distributor Cap Replacement is between $299 and $380 but can vary from car to car.