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The word "tune-up" actually applies only to older cars, on which a mechanic can perform the traditional work associated with the term:    spark plug replacement,   ignition contact point replacement,   dwell adjustment.

ignition timing adjustment,    carburetor idle,   mixture adjustment.

 

An automotive tune-up is a the inspection, diagnosis, testing, and adjustment  necessary  to  maintain  peak engine performance or restore the engine to original operating efficiency.  For most of today's cars, “engine performance maintenance” is a more accurate term.   All modern cars and  light  trucks  are  equipped  with electronic ignition (no points) and at least an on-board computer that automatically adjusts items like:

 

a. ignition timing

b. fuel mixture, and

c. idle speed

 

In fact, on modern computer-controlled cars, it is impossible to adjust the ignition timing, fuel mixture and

idle speed by yourself.

 

On an electronic-ignition system, the basic tune-up procedures are as follows:

 

1. Remove spark plugs.

2. Test the compression in each cylinder.

3. Clean or replace spark plugs and gap spark plugs to manufacturer’s specifications. Install in engine.

4. If applicable, check the distributor cap and rotor for cracks and wear. Replace if necessary.

5. Use a tachometer to set idle speed to specifications (if adjustable).

6. Use a timing light to set initial timing (most electronic ignition systems do not require adjustments).

 

The list above represents only the “basics” about tune-ups.   Other functions that could be performed include using an emissions analyzer to check for compliance with emissions standards and f or  fuel  economy,  and measuring  vacuum  and  checking  for leaks with a vacuum gauge.  The  tune-up  is  a  good  opportunity  to perform a general preventive  maintenance  check  on  everything in  the  engine  compartment, and look for

failed or about to fail components such as:

 

loose or damaged wiring,

leaking fuel lines,

cracked coolant hoses, and

frayed belts

 

Spark plug life and efficiency depend upon the condition of the engine and the combustion chamber temperatures the plug is exposed.   These temperatures are affected by factors, such as compression ratio

of the engine, air-fuel mixtures, exhaust emission equipment, and the type of driving you do.

 

Replacing Spark Plugs

New technologies in spark plug and ignition systems like the platinum spark plugs  have pushed the replacement interval to 60,000 miles (96,540 km) or even 100,000 miles (160,900 km). Again, this depends

on car usage and driving conditions.

 

A set of standard spark plugs usually requires replacement after about 20,000-30,000 miles (32,180 kms - 48,270 kms) on cars with electronic ignition.   These figures are also dependent on your particular style of driving.   The electrode on a new spark plug has a sharp edge, but with use, this edge becomes rounded by wear, causing the plug gap to increase.

 

Distributor Cap Inspection

At every tune-up, visually check the distributor cap and rotor for damage, burns or corrosion.   Check the

spark plug towers and their terminals under the cap to be sure they are free of corrosion that would inhibit proper spark distribution.   Replace any damaged or worn components.   Inspect the rotor for cracks, excessive burning of the contacts, and mechanical damage; and replace as necessary.   While primary wiring is less perishable than secondary circuit, it should be checked for cracked insulation or loose connections.   Tighten connections or replace wires as necessary.  If the spark plug wires have become unserviceable due to time and wear, it is a good idea to replace the cap and rotor as well.

 

Ignition Timing

On many late model cars, the ignition timing is completely controlled by the on-board computer and is not adjustable.   On older cars, this was accomplished by centrifugal weights within the distributor along with a vacuum diaphragm mounted on the side of the distributor.   Later cars are equipped with an electronic spark timing system in which no vacuum or mechanical advance is used.