Engine Tune-Up

Introduction

Tune-up procedures have changed in recent years and are done as part of routine maintenance rather then correct a drivability problem

New engine can run for longer periods between tune-ups. Most new engines do not require spark plug replacement for up to 100,000 KM

Engine Tune-up

Ensures that the engine , ignition system, fuel system and emission control systems are with in factory specification

Auto manufacturers normally recommend a maintenance tune-up after a specific engine operating period, based on mileage and vehicle use

Minor Tune-up

Involves parts replacement and fluid replacement, filter and spark plug replacement

A vehicle with 40,000 KM to 60,000Km may only require a minor tune-up

Minor Tune-up

Typically involves these tasks

1. Visual inspection of the engine compartment

2. Replace spark plugs3. Replace

oil/filter/lube4. Replace air/fuel filter5. Ignition service

points or timing 6. Check for fault

codes

Major Tune-up

Besides the steps listed for a minor tune-up a major tune-up requires more diagnostic tests using a scan tool, gas analyzer or a compression gauge

Major Tune-up

1. Replace drive belts2. Replace brake,

transmission, differential and other fluid

3. Replace weak engine sensors e.g. O2,

4. Replace spark plug wires

Importance of a tune-up

A tune-up is very important to the operation of an engine. It can affect:

• Engine power and acceleration• Fuel consumption• Exhaust pollution• Smoothness of engine operation• Ease of starting• Engine service life

Tech Tip

If a computer controlled vehicle has performance problem, such as a rough idle, stalling, surging, a tune-up will not correct the condition in most cases.

Performance problems in many newer vehicles are caused by the failure of an engine component, or sensor.

Questions

Spark Plugs

The spark plugs use high ignition voltage to ignite the fuel mixture

between 4000 and 28,000 volts is needed to jump the gap at the electrode

Spark plug reach

Reach is the distance between the end of the plug threads and the seat or sealing surface on the plug shell

If the reach is too long the plug electrode might contact the piston

Or too short won’t reach

the combustion chamber for complete burn

Types of Plugs

Resistor spark plug the plug wire has an internal resistance designed to reduce static in radios most newer vehicles require resistor plugs

Used of Fuel injected vehicles to reduce E.M.I

Non Resistor spark plugs

Has a solid metal rod forming the center electrode

Not very common in street applications but found on racing or off road applications

Spark plug Gap

Is the distance between the center electrode and the side electrode

Spark Plug Heat Range

Is a rating of the operating temperature of the spark plug tip

Is determined by

the length and diameter of the tip and the ability for the plug to transfer heat

Hot Plug: long insulator tip and will burn off deposits

Cold Plug: has a short insulator tip will prevent over heating and preignition

Manufactures will specify heat range

Hot/Cold Plugs

Spark Plug Replacement

1. Grasp the spark plug boot pull the wire off the plug will twisting back and forth

2. Use compressed air to remove debris away from the spark plug hole

3. As you remove each plug lay it out in order so you can read them

4. Set the spark plug gap on the new plug refer to specs.

5. Use anti seize on threads (aluminum head)

6. Use your fingers to start the plug in the hole (short piece of vacuum hose)

7. Once started use the socket and ratchet to tighten it up

(spark plug sockets have rubber boot inside)

Spark Plug Gap Gauge

THE STYLE IS USED ON A PLATINUM TIP PLUG STANDARD SPARK PLUG

Engine Compression Testing

It is frequently made during a tune-up to check the engine’s mechanical condition

If a engine fails the compression test mechanical repair must be made before the tune-up

Compression Test

Is used to measure the amount of pressure during the engine compression stroke

If the compression readings are not within spec. something is mechanically wrong with the engine

It should be done anytime there is an extremely rough idle, a popping noise from the air inlet or exhaust, excessive blue smoke and blow-by

Exhaust Smoke Readings

Blown Head Gasket

A blown head gasket can cause pressure, coolant and oil leakage

This blown head gasket allowed compression stroke pressure to flow into adjacent cylinder

Gasoline Engine Compression Test

1. Remove all the spark plugs so the engine can rotate easily

2. Block open the throttle plate this will prevent a restriction of air flow

3. Disable ignition system to prevent sparks

4 If its fuel injection it should also be disabled

5 Thread the compression gauge into one of the spark plug holes

6 Crank the engine allowing it to rotate 4 to 6 compression strokes

7 Write down the gauge readings and repeat these steps

Wet Compression Check

Should be completed if a cylinder pressure reads below specifications during a standard compression check

This will help determine what engine parts are causing the problem

Wet Compression Test Procedure

Squirt A tablespoon full of 30 weight motor oil into each cylinder with the low pressure readings

Install the pressure gauge and recheck

(warning do not put too much oil in or there will be false readings )

If the compression gauge readings increase with oil in the cylinder then piston rings or cylinder is worn out

If the pressure remains the same then valves or head gasket may be leaking

The oil will seal a ring but not a burned valve or head gasket

Compression Test Results

Normal compression readings will make the gauge increase evenly to spec.

The pressure should not vary more then 15 to 20 psi in each cylinder

General spec for gasoline engine 125 to 175 psi

Check service manual for the manufacture spec.

Causes of low Compression

Burned valve Burned valve seatPhysical engine damage Blown head gasket Worn rings or cylinderValve train trouble

(Broken valve spring)Jumped timing chain or

belt

Questions

1. What is a compression test?

2. Why do we want to perform a compression test?

3. What are some examples of engine compression problems (smoke )

4. What is a general specification of a cylinder compression reading?

5. What can a Wet cylinder compression test tell us?

Summary

An engine tune-up returns the engine to a condition of peak performance

A minor tune- up is a basic tune-up done when the engine is in good operating condition

A major tune –up is more thorough and is done when the engine systems (ignition, fuel, emission ) are in a worn condition

Summary

Depending upon the age and condition of the vehicle any number of parts may need replacement during a tune-up

With modern computer controlled vehicles never reroute wires. Keep all wires in there original location

A compression test is frequently made during a tune-up to check the engine’s mechanical condition

Diesel engines do not require tune-ups like gasoline engines they do not have spark plugs or ignition system to fail

Signs Of Engine Problems

Heat Range of Spark Plugs

Spark Plug Reach

Reach is the distance between the end of the plug threads and the seat or sealing surface on the plug shell

Compression Test Results

Is used to measure the amount of pressure during the engine compression stroke

The pressure should not vary more then 15 to 20 psi in each cylinder

A wet compression test the oil will seal a ring but not a burned valve or head gasket