Tune & Tune Checks

People have an incredibly wide range of perceptions as to what a tune-up entails.

Both among consumers and shops, this range includes everything from the most minimal possible of simply replacing the spark plugs, on out to include spark plugs and filters and a full major 60k or 90k service with all the fluids being changed and the timing belt replaced also.

The following tune description is a composite description that describes tune procedures for vehicles with several generations of developments, including:

• Carbureted and fuel injected. Those with vacuum advance and mechanical advance and those that have electronically controlled timing.
• Ignition systems with distributors and distributorless ignition systems with ignition coils directly over the spark plugs.

• Vehicles with no onboard diagnostics built in; vehicles with first-generation onboard diagnostics that are accessed through jumper wires and blinking-light codes; and vehicles with second-generation diagnostics that are accessed through full computer hook-up.

Our composite working definition is below:

• Test drive before beginning
• Scan test if OBII (onboard diagnostics 2nd generation)
• Scope check those that allow standard inductive hook-up to secondary ignition
• Replace spark plugs
• Replace air filter if dirty, and the fuel filter for carbureted models
• Full voltage test of rotor (those that allow standard inductive hook-up)
• Wet test cap & wires for voltage leaks. Check insulators for leakage where they pass through spark plug tubes.
• Manually check high-tension connections at coil and cap for corrosion
• Note whether cap, rotor & wires are factory or aftermarket
• Clean top surface of coil (coil-in-cap models)
• Check and adjust timing when applicable
• Does jumper connection cause timing to change?
• Verify that TPS contacts are engaging. If necessary, bypass to set timing. (Bottom two terminals on most) Mechanical advance free?

Vacuum advancer:

• Diaphragms not ruptured?
• Able to move breaker plate?
• Gets proper vacuum signal?

Check EGR system.

• Does EGR valve get vacuum signal?
• Does EGR kill engine or cause a significant rpm drop at idle

O2 sensor

• Cycles back and forth quickly?
• Operates over full range when made lean and rich?

EFI:

• Check whether throttle valve sticks in throttle body.
• Adjust idle speed when appropriate. Emphasize smooth idle & not dieseling over exact rpm specs.
• Carbureted: Clean and lubricate choke
• Some carbureted: Drill & adjust mixture (only on accessible carbs) when exhibiting lean idle condition.
• Cleaner and penetrating oil through auxiliary air regulator
• Compression check if engine running suggests problem Quick check emissions if:

Car approaching license renewal date
Symptoms suggest emission reading could give useful diagnostic information

Check fluids in engine compartment
Test drive again after work completed