It depends. At one time, a tune up was more complicated, today there isn't much left on a car to tune up. A tune up of most modern cars may be simply to replace the spark plugs, and possibly the spark plug wires. Many of the adjustments that were needed in the past are no longer needed, or are continuously handled by the computer. A mechanic today can check the computer for stored error codes it has detected in the sensor readings. Sensors are used to measure engine temperature, air temperature, air pressure, oxygen content in the exhaust, throttle position, and various other items. The computer uses the data to calculate the timing, fuel injection, and in some cars transmission shift points. A tune up may involve replacing a sensor that has failed.
Some things a tune up might include:
Change of spark plugs. Check / change spark plug wires. Check / change air filter. Change fuel filter. Check computer for error codes. Check belts and hoses Change distributor cap and rotor. (Many newer cars do not have) Adjust carburetor (if equipped, most newer cars use fuel injection.) Test drive of vehicle Clean fuel injectors (either with a pressure cleaning machine or bottle of injector cleaner in fuel tank) Battery test. Other ( ask the shop or mechanic )
On older cars (generally early or pre 1970s)
Each shop or mechanic may have a slightly different idea of what a tune up is. If you take your vehicle in for a tune up, ask what services will be performed. If you have been having some problems with the car, a list of problems that occur, and conditions when they occur, can help the mechanic diagnose the problem. From one shop to another services, and cost, will vary.
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