Poor braking effectiveness indicates not only the case where the brake does not operate at all even when the brake pedal is depressed, but also the case where the brake effectiveness is weak against the depressing force or there is no pedal feel. When troubleshooting poor braking effectiveness, it is vital to have a thorough compensation of the technical aspects in order to understand why the braking effectiveness worsens.

Poor braking effectiveness mainly occurs under the following conditions.
1. When there is a malfunction in the brake system
2. When the vacuum pressure in the brake booster is not maintained
3. When fade phenomenon or vapor lock occurs
4. When the vehicle gross weight is increased due to passengers or laden weight
5. When driving on a submerged road
6. When the friction coefficient changes between the tire and the road surface

Poor Braking Effectiveness

1. In the case when there is a malfunction in the brake system
Trouble in the brake system usually occurs in the rubber parts of the hydraulic system such as the brake hose, the piston cup, etc. Long -term use of the rubber parts in the system results in deterioration, which causes fluid leakage. Moreover, emergency braking may result in a deteriorated part bursting suddenly, causing the braking system to lose control. There are two brake hydraulic systems in the brake system concerning safety. However, when either of these systems have a malfunction, braking will be affected.
2. When the vacuum pressure in the brake booster is not maintained
If the engine stalls while driving, the vacuum pressure in the booster is not maintained. Pressure in the booster is not secured. In this case, the brake functions correctly only once. The brake pedal will feel heavy and the brake seems to be ineffective after the second trial.
Even when the booster does not operate, it does not mean that the brake effectiveness is not gained. If the driver fully depresses the brake pedal, braking is effective although the deceleration rate is less than normal.
3. In the case where fade phenomenon or vapor lock occurs
Fade phenomenon
The resin contained in the friction materials of the pad and shoe produce gas when the temperature of the pad and shoe increases. Poor braking effect results if the gas that acts as a lubricant reduces the friction coefficient. The fade phenomenon tends to occur especially during the initial period because the pad and shoe contains appropriate conditions for producing the gas.

Poor Braking Effectiveness
The thermal history can be checked by disassembling the brake unit responsible for the fade phenomenon.

Vapor lock
The driver doesn’t feel any reaction from the brake pedal and the braking effect is reduced when bubbles occur in the brake fluid. The bubbles are produced when the heat in the pad and shoe is transferred to the brake fluid and the fluid boils.

Conditions causing vapor lock
• After stopping a vehicle, the brake unit is not cooled down by
sufficient airflow.
• The brake fluid is not changed for a long time.
Be sure to remove the air from the fluid. Once the vapor lock occurs, bubbles remain in the piping although the brake pedal operating force returns to normal after the brake cools down.

4. In the case where the vehicle gross weight is increased due to passengers or laden weight
As the vehicle weight becomes heavier, stopping inertia becomes greater. The stopping distance will be longer even if the brake pedal is depressed with the same force.
5. In the case where driving on a submerged road
Temporary poor braking effect is caused by the low friction coefficient due to the lubricating action of the water when the friction material in the brake becomes wet. Repeated braking allows the water to evaporate and regain the braking effect with friction heat.
6. When the friction coefficient changes between the tire
and road surface
Tires tend to slip and the stopping distance becomes longer when running on a wet or snow covered road or using worn tires. If emergency braking is applied under such conditions, tires will lock and make the vehicle unstable resulting in a spin.

Braking and Pedal Operating Force Check
1. Maximum braking force check
Measure braking force using a brake tester
Criteria
There must be no difference when comparing with another vehicle of the same model.
2. Compare the breaking force and pedal operating force
Measure the breaking force and pedal operating force using a pedal effort meter and brake tester.
Criteria
There must be no difference when comparing with another vehicle of the same model.

What is brake squeaking?
Brake squeaking is a vibrated symptom caused by the friction between the pads and rotor. This vibration is transmitted as a sound. This symptom is referred to as “self-excited vibration,” and differs from the “forced vibration,” such as body vibration. Self-excited vibration produces a further vibration to itself and as the vibration becomes stronger, the energy becomes greater.

Sound generation and how the sound is transmitted
Brake squeaking is compared to a howling phenomenon. The howling phenomenon is produced by the following process: a sound enters the microphone from the speaker, amplified by the amplifier, repeatedly comes out of the speaker, and finally becomes louder sound. If this symptom is compared to a brake, it is as follows. Speaker: rotor Microphone: pads Volume level of amplifier: coefficient of pad friction Distance between the microphone and the speaker: attenuation (effectiveness of the shims)

Construction of Brake and Brake Squeaking
In the case of self-excited vibration, once a vibration is generated, the vibration is amplified and it becomes greater. As the amplitude becomes larger, greater attenuation will be required to stop the vibration. In the brake construction, pads and the rotor contact closely, so it is difficult to attenuate the vibration.

Generated frequency
In the case of brake squeaking, the generated frequency varies. Even if brake squeaking at a certain frequency is reduced, another brake squeaking will be generated at different frequency. The frequency varies depending on the model and it is difficult to reduce anything more than the general vibration. The effectiveness of the reduction sometimes appears, but sometimes it does not appear.

The relationship between the brake squeaking and the brake
Brake squeaking is generated by the friction between the pads and the rotor, so there is a correlation between the pad friction coefficient and brake squeaking. Therefore, the prevention of brake squeaking and the improvement of brake effectiveness are rather difficult to achieve at the same time. In fact, a large amount of energy is transmitted to the rotor in the pads that are effective, the brake squeaking tends to occur. Conditions that tends to cause brake
squeaking

• When the vehicle is left or the brake is cooled
Brake squeaking tends to occur due to the increase of the brake pad friction coefficient caused by the oxidation of the rotor and pads surfaces, or pad moisture coef absorption. Fi absorption.
• When the brake is cooled down under high temperature conditions
When the temperature of the pad is over 200 degrees centigrade, the resin inside the pads decomposes and the pad surface loses its abrasiveness. When the temperature then drops, the friction coefficient increases. As a result, the brake squeaking tends to occur.
When the temperature of the pad becomes high, the paint on the sides sometimes become whitish, helping to judge the thermal history.
• When the rotor ground trace cannot be seen
When the abrasive chips of the pad attaches to the rotor surface, the rotor surface is ground by the pads, accordingly. When the surface irregularity decreases, the friction coefficient increases. As a result, the brake squeaking tends to occur.
Brake squeaking reproduction test
• Perform this test by altering the pedal depressing force on a slope.
• Increase the brake temperature and leave it for 30 minutes. Then perform this test.
• Leave the brake overnight to decrease the brake temperature. Then perform this test.

Brake Squeaking Reducing Method
• Inspection of the anti-squeal shim and application of
grease
Check for peeling or warping of rubber on the anti-squeal shim surface. Apply grease to the grease pan and claw of the anti-squeal shim. By using grease, this procedure improves the attenuation force and changes the contact between the calliper and pad.
• Piston back
Press the piston of the calliper back once. In this procedure, correcting the gouging of the piston and sliding it smoothly helps to maintain the stable contact of the pads.
• Pad backing inspection and repair
Check for warping of the pad backing. If warping is found, grind the backing. This procedure helps to even the contact of the piston and calliper claw to the pads.
• Pads torque reception surface fi le and grease application
Check the contact truck. If the pads contact unevenly, fi le the surface with sandpaper to correct it so that it evenly contacts with the calliper mounting. Apply grease to the torque reception surface. This procedure helps to reduce the friction to the torque reception surface and to make the pad stable.

The cause of vehicle pull is sometimes on the vehicle side and sometimes due to the road conditions or customer’s habitual usage. When performing troubleshooting for vehicle pull, it is important to understand the cause of it.

Judgement of vehicle pull
It is difficult to judge vehicle pull by using an electrical tester, etc. So, perform a road test and judge whether it is a malfunction or not.
• Compare with another vehicle of the same model
• Measure how much it moves within a certain distance
Measure how many meters the vehicle offsets in 100 meters.

Cause of vehicle pull
• Force generated on the tire
• Influence of alignment
• Influence of road surface

Force Generated on the Tire
The force generated on the tire may cause vehicle pull. The typical phenomenon is shown below.
• Ply steer
The transverse direction force is generated due to the ply direction of the tire belt. When the tires are rotated straight ahead, the force that tries to move the tires in the transverse direction along the ply is referred to as ply steer.
• Conicity
When applying a lateral force to the surface of a standing tire, portion contacting with the ground will alter shape evenly. However, unevenness of the tread, the force that returns it to the original shape is not equal. If rolling the tire in this condition, the tire rolls in the direction where the reaction force is smaller. In this condition, the force in the transverse direction is referred to as conicity. Inspection methods regarding whether the force generating on a tire affects vehicle pull or not.
• Change the left and right tires. Or remove the tire from the wheel and reverse.
Ply steer: The direction does not change at all.
Conicity: The direction changes.
Infl uence of Alignment
Vehicle pull occurs when there is an imbalance between the forces: moving to the right and to the left.
Alignment that has conformity with vehicle pull.
• Difference between right and left of cambers Moves to the positive (+) side
• Difference between right and left of casters Moves to the smaller side
• Difference between right and left of the king pin angles Moves to the negative side when braking

Influence of Road Surface
As for trails, each centre of contact on the ground between right and left are different, so the king pin offset dimension of the right and that of the left differ. Therefore, since the moment around the king pin axis differs between right and left, the steering wheel moves to the side where the moment is larger.

Influenced conditions
• Depth of the trails:
As the trail becomes deeper, the level becomes larger.
• Width of the tires:
As the tire width becomes wider, the level becomes larger.
• Tire tread rigidity:
As the tire tread rigidity becomes higher, the level becomes higher.
Some roads are slightly sloped for drainage. For this reason, the steering becomes unstable in only a specific place, or the direction differs when going somewhere and returning to the original place.

Abnormal Sound and Noise Caused by Abnormal Combustion
3. After fire
Air fuel mixture is discharged without completely being combusted inside the combustion chamber. This unburned gas is retarded in the exhaust system and burnt comexplosively. bustion explosively. When the air fuel mixture is excessively rich, and the ignition timing slightly retards, this phenomenon may occur.
Main cause
• Air fuel mixture is excessively rich
There is an oxygen shortage and the air fuel mixture cannot be combusted completely.
The unburned gas is heated in the exhaust pipe, and “after fi re” occurs.
• Sudden deceleration and shifting down
Intake pipe vacuum pressure suddenly rises and the air fuel mixture becomes excessively rich.
Since charging efficiency also worsens, the two elements of “good compression” and “good air fuel mixture” are not satisfied. As a result, the combustion becomes unstable and “after fire” tends to occur.
• Ignition timing retards
Combustion duration becomes longer, the combustion process continues until the end of the explosion stroke and after burn occurs.
• Misfire
Sometimes misfire occurs due to a malfunction in the ignition system.
Unburned gas is heated in the exhaust pipe and after fi re occurs.
4. Back fire
This symptom occurs as a result of the air fuel mixture being taken in is combusted.
This is because the combustion process still continues even when combust commotion in the cylinder becomes slow and when the intake valve opens in the case of busted. Combustion Combus excessively
lean air fuel mixture or ignition timing retardation, etc. excessively “Back fire” tends to occur when starting while the engine is cold when accelerating during warm up.
Main cause
• Air fuel mixture is excessively lean
Combustion becomes slow and the combustion duration becomes longer. When the combustion process is not completed in the explosion stroke and continues to the next intake stroke, “backfire” occurs.
• Heat spot occurs
When heat spot occurs due to overheating, the air fuel mixture is ignited in the intake stroke. The air fuel mixture is combusted in the intake manifold and “backfire” occurs.
• Inappropriate valve timing and ignition timing
If these timings are inaccurate due to mis-operation, back fi re occurs and the engine does not run.

Mechanically Abnormal Sound and Noise
The engine consists of many parts, and each part operates by a sliding or rotational movement. The portion that slides or moves by rotational movement has clearance without exception and when this clearance becomes larger than the specification, an abnormal sound or noise can be heard.
The sound resulting from abrasion in the engine has the following characteristics
1. Occurrence condition
• When the engine is cold, the sound is loud.
• When the oil viscosity is insufficient, the sound is loud.
• When the hydraulic pressure is low, the sound is loud.
• When accelerating, the sound is loud.
• When the load is heavy, the sound is loud.
2. Sound types
• Sliding sound: the sound of things rubbing together.
• Hitting sound: the sound produced by hitting.
• Other sounds: Generally obscured and complicated sounds.
• Sound when idling
• Sound in the specified engine speed range
• Sound at various engine speed range
Abnormal Sound and Noise Caused by Abnormal Combustion
1. Knocking
During acceleration, a high-pitch hitting sound is produced.
The piston and the valve receive a bad influence and the engine may be damaged.
Main cause
• Poor fuel quality
Octane number of the fuel is lower than the required
• Ignition timing is advance
If the ignition timing is advanced, combustion is performed suddenly. As a result, knocking occurs.
• Spark plug failure
The overheated spark plug becomes a heat spot and causes pre-ignition. Suitable temperature for spark plug: approximately 450 to 950 degrees centigrade (self-cleaning temperature)
• Carbon accumulation in the combustion chamber
If carbon accumulates in the combustion chamber, the carbon prevents the heat from being dissipated and the engine overheats. The heated portion becomes a heat spot and causes pre-ignition.
• Air fuel mixture ratio is lean
During high speeds and with a heavy load, if the air fuel mixture ratio is lean, knocking will occur easily.
• Over load operation
When the engine load is excessive, knocking will occur easily. If the vehicle is continued to be driven while knocking occurs, the malfunction as shown below could occur.
• Overheating
• Metal damage due to engine overheating
• The amount of fuel consumption increases due to reduced heat efficiency
• Spark plug, piston and valve melt down.
• Cylinder head gasket breakage.
2. Run on (dieseling)
This is a phenomenon in which spontaneous combustion occurs. This phenomenon is caused when the fuel sucked in by the inertia of the crankshaft or fl ywheel, overheated spark plug that ignites the unburned gas and the carbon accumulated in the combustion chamber becomes a heat source even after the ignition switch is turned off. In an EFI engine, when the ignition switch is turned on, the fuel stops. Therefore, run on does not occur.
Main cause
• Inappropriate fuel
The fuel self-ignition temperature or octane number is low.
• High intake temperature
The compressed air fuel mixture temperature becomes higher than the self-ignition temperature.
• High-pressure compression (high-speed, high-load running)
Combustion temperature and the combustion chamber wall temperature are both high. When the pressure is high, the compressed air fuel mixture temperature also becomes high.
• Carbon accumulation inside the combustion chamber
When carbon accumulates inside the combustion chamber, the carbon prevents the heat from being dissipated and the engine overheats. The overheated portion becomes a heat spot.
• Spark plug failure
Spark plug is over-burned and becomes heat a spot.
• Idling speed is high
The amount of intake air when the throttle valve is fully closed is large.
• Engine overheating
Temperatures of combustion chamber parts become higher.
• Ignition timing retards
The maximum burning temperature lowers, but the combustion duration becomes longer and the exhaust temperature becomes higher. The temperature near the exhaust valve rises and becomes the heat source of the spontaneous combustion.

The amount of engine oil absolutely reduces by running. The passages into which the engine oil flows to lubricate each part of engine consists of the passage to the oil pan and to the combustion chamber or to enter exhaust gas without not returning to the oil pan. The engine oil entered the combustion chamber and exhaust gas is burnt.
The passage in which the oil reduces
• The passage through which the oil lubricating the cylinder wall enters combustion chamber.
• The passage enters the combustion chamber from the gaps between the valve stem and the valve guide bush.
• The passage through which the oil contained in the blow-by gas is sucked into the combustion chamber with the gas.
• The passage through which the oil that lubricating the turbocharger bearing passes from the compressor side to the combustion chamber and from the turbine side to the exhaust gas.
The cause infl uences the amount of oil consumption
• The amount of oil entering the combustion chamber increases due to engine malfunction.
• The engine malfunction occurs due to oil maintenance failure.
• The amount of oil consumption changes depending on the habitual usage and driving method.
Important points to remember when measuring the oil
Inspection timing
Immediately after the engine stops, the oil has not completely returned to the oil pan from the cylinder head, therefore, the oil level is lower. Also, when filling oil, it takes time to for it to reach the oil pan. As a result, the oil level is low if the level is checked immediately after the oil has been filled.
Oil temperature
When the oil temperature is high, the oil expands, so the oil level becomes high.
When the oil temperature is low due to insufficient warm up, the viscosity is high and the returned oil amount to the oil pan from the cylinder head becomes reduced. As a result, the oil level becomes low.
Inspection place
When parking the vehicle in an inclined place, the oil surface in the oil pan inclines and the oil level cannot be measured accurately.
Measure the Oil Consumption Amount
(1) The oil surface level in the oil pan differs depending on the vehicle inclination, oil temperature and the amount of returned oil from the cylinder head. Inspection should be performed under the same conditions.
Oil level inspection conditions
• A level surface
• Engine warming up (water temperature 80 degrees centigrade)
• Measure the oil level fi ve minutes after the engine stops.
(2) The required period of measurement can be calculated based on the customer’s running distance for a month and the consumption amount.
(3) Measure the fi lled oil accurately using a measuring cylinder. In the customer’s measurement, the difference is large and reliability is low, therefore, accurately measure the consumption amount. It is necessary to judge whether the amount is appropriate or not based on the result.

Oil Degradation and Abrasion Inside the Engine
If the oil and oil filter is not changed periodically, the engine oil degrades. When the oil degrades, not only the consumption amount increases, but also the abrasion inside the engine is accelerated and the amount of oil consumption further increases.
• Oil degradation
If the oxides, abrasion chips, soot, moisture, etc. produced by being burnt mix into the oil, the oil degrades, and the purifi cation or lubrication performance decreases. In a diesel engine, the soot mixes into the oil, the oil viscosity becomes higher, the scrape off performance of the oil lubricating the cylinder becomes worse. As a result, the amount of oil mixed into the combustion chamber increases. Compared to a gasoline engine, diesel fuel contains much more sulfur and acids are found in the burnt gas. Therefore, diesel engine oil is more easily degraded than gasoline engine oil. If the oil change period for a diesel engine is the same as that for a gasoline engine, engine abrasion is abnormally accelerated.
• Abrasion inside the engine
When the oil is degraded, sludge, etc. is produced. Therefore, the abrasion inside the engine is accelerated and the oil loss via the piston rings and the valve guides occur.
(1) Oil loss via the piston rings
If the cylinder wall or the piston rings are worn, its oil scraping off performance worsens. Therefore, the amount of oil consumption increases. If the piston rings and the ring groove are worn, the ring pumping performance increases and the oil amount pumped into the combustion chamber increases. Therefore, the amount of oil consumption increases.
(2) Oil loss via the valve guides
If the valve stem, the valve guide bush and the oil seal are worn, the oil amount entering the combustion chamber increases. Therefore, the amount of oil consumption increases.
The Cause of Increased Oil Consumption
1. Laden conditions
As the number of occupants and items increases, the engine load becomes larger. As a result, the acceleration pedal is depressed more than usual. Therefore, the compression pressure and the combustion pressure becomes higher. Accordingly, as the force that presses down the piston or shock becomes larger, the piston inclines in the cylinder or the shape of the piston ring alters, thus the oil splashing lubrication performance becomes worse. Furthermore, since the cylinder and the piston temperature becomes higher, the engine oil vaporizes and the amount of consumption increases. In a diesel engine, since the fuel injection amount increases when the load is heavy, more soot is produced and the oil degradation is accelerated.
The Cause of Increased Oil Consumption
2. Oil loss when the engine brake is used
When the engine brake is applied, the vacuum pressure is high, therefore, the amount of oil entering the combustion chamber increases and the oil consumption increases. When driving on a highway or uphill, the vehicle speed is often controlled by acceleration operation, so the using frequency of the engine brake becomes high and the amount of oil consumption increases.
3. High engine speed
As the engine speed becomes higher, the piston moves more quickly. Therefore, it is more difficult for the piston ring to splash lubrication the oil on the inside of the cylinder wall. Furthermore, the amount of oil that the crank shaft scrapes off also increases, and the oil supply increases. As a result, the amount of oil consumption increases.
4. In the case of a vehicle with turbocharger
In the case of a vehicle with turbocharger, the oil is exposed to high temperatures (approximately 700 degrees centigrade), so oil degradation is quicker. Further, the turbo charger applies a heavier load, so as a result, it consumes a greater amount of oil.

Customer Usage?
1. Warming up and running distance
A long period of warm-up will waste the fuel. When the engine is cold, more fuel is required and the idling speed is high due to fast idling. Based on these facts, when the running distance is short, the running time ratio when the engine is cold increases and the fuel consumption increases.
Warming up
To improve fuel consumption, reduce the warming up time as much as possible. Even in winter, stop warming up when the water temperature indicator begins to move (water temperature 40 to 50 degree centigrade).
2. Laden condition and the number of occupants
As the load and the number of occupants increase, the weight becomes heavier and fuel consumption increases.
3. Use of air conditioner
When turning the compressor of the air conditioner, engine power is used, increasing fuel consumption. The operation rate of the compressor increases as the temperature and moisture becomes higher. The amount of air blow decreases as the vehicle speed lowers, and the cooling performance of the condenser becomes worse. Accordingly, the load applied to the engine increases. Therefore, on a congested road when the temperature is high, fuel consumption increases by 20 to 30 %.
4. Electrical load
The load to the alternator increases as the quantity of electricity used increases, so fuel consumption increases.
5. Running in the city and on congested roads
Running under these conditions increases the fuel consumption, because the average vehicle speed is low, the amount of time the vehicle is stopped becomes longer, and frequent acceleration and deceleration is performed. On a intermittently congested road where there is frequent acceleration and deceleration, the fuel consumption will be greater than on a road where the vehicle speed is considerably low.
• Average vehicle speed Average vehicle speed can be simply calculated by distance and time. But when the vehicle runs long distance, there are congested roads and not congested roads during this running, so it is necessary to obtain each value by separating a certain block. In this case, it is necessary to clearly separate the ratio between the lows peed and high-speed running distances.
• Vehicle stoppage time When the vehicle stops, fuel is consumed, however, the running distance is 0 km, so the fuel efficiency becomes 0km/l. As the stoppage time becomes longer, fuel efficiency worsens
Customer Usage?
6. Running on the highway
On highways, When the vehicle runs at a constant speed, the fuel consumption often increases. But when the speed rises, the fuel consumption increases. Generally, decreasing a speed of 100 km/h to 80 km/h, the fuel consumption is reduced by 10 to 30 %.
7. Starting and accelerating
Fast start or sudden acceleration consumes more fuel than usual in order to reach the same distance or speed. Generally, a fast start or sudden acceleration consumes fuel equivalent to the amount consumed by running run approximately 100 m. To reduce fuel consumption, maintain a certain vehicle-to-vehicle distance and constant speed.
8. Wasting acceleration operation
Racing consumes fuel equivalent to the amount consumed by running approximately 50 m.
9. Shift operation
Generally, unless the driveability worsens, such as the occurrence of knocking, using a higher gear and making the engine speed lower will reduce the fuel consumption.
How is it Measured?
Many customers calculate fuel consumption by the full tank method. However, calculation by this method can lead to different results. Therefore, it is necessary to pay attention to the following points.
1. Fuel filling method and difference
When fuel is filled in the tank after running, the amount has to be equal to that before running. However, vehicle inclination, the person who fills, filling speed, etc. are not same, so the amount filled will be different. Accordingly, the calculated result for fuel consumption will be different.
How is it Measured?
2. Fuel filling timing and difference
When fuel is filled when only a small amount has been consumed, the running distance is also short. Therefore, the fuel consumption under this running condition can be calculated. On the other hand, when fuel is filled when the tank is almost empty, the running distance is long and the vehicle has been exposed to a variety of running patterns. Therefore, the fuel calculation result will be an average of the total results.
3. Important points to remember when measurement
To calculate the fuel consumption accurately, perform a road test based on the diagnostic questioning, with a fuel consumption meter and a hand-held tester attached and record data that shows the change in fuel consumption under different road conditions and driving methods.

Increased fuel consumption frequently is a result of the vehicle usage and road conditions rather than vehicle malfunction. Therefore, it is important to accurately understand the customer’s habitual usage and required level. In this chapter, the items regarding the estimated causes of increased fuel consumption are explained.
• Since when?
Understand the relationship between engine warm-up and A/C usage, the change of the vehicle condition and the malfunction.
• Compared to what?
Find the difference between the target vehicle that the customer compares and the customer’s vehicle and troubleshoot the cause of the increased fuel consumption.
• How is it used?
Troubleshoot the cause of the increased fuel consumption based on the customer’s usage.
• How is it measured?
Troubleshoot the cause of the customer’s measurement error.
Since When?
1. Seasonal variation of fuel consumption
When the air conditioner is used in summer, fuel consumption increases. The degree of increase depends on the air conditioner load which is affected by the temperature and moisture. In winter, the fuel consumption also increases, because fast idling is performed for longer than the usual in order to warm up the engine.
2. Fuel consumption change over time
Knocking occurs because carbon in the combustion chamber accumulates for a long period of time. Knock control retards the ignition timing increasing fuel consumption. If the ignition timing retards by fi ve degrees, the fuel consumption increases by approximately 6%. When a brand new vehicle runs approximately 5,000 to 10,000 km, the fuel consumption decreases by 5 to 10 %. This is because the friction to the engine, drive train, tires, etc. is reduced.
3. Rapid change in the fuel consumption
“Fuel consumption has increased a lot compared to last year,” “Suddenly, the fuel consumption has increased, ” a sort of malfunction may have occurred to the vehicle.
Compared to What?
1. Difference in the engine
• In general, fuel consumption is greater when the engine displacement is larger. The main cause being that friction increases as the engine is larger and the vehicle weight is heavier.
• The fuel consumption in the normally used range is almost the same despite of the characteristics of the engine; an engine that has great torque at a low speed and that has great at a high speed. The gear ratio of the engine that has great torque at a low speed is set smaller, however, in this case, the fuel consumption can be said to be decreased.
• In an engine equipped with a turbocharger/supercharger, the driver frequently
depresses the accelerator pedal more than is necessary, because of its slow reaction when moment of starting and accelerating. As a result, the turbocharger/ supercharger functions, starting the acceleration to be greater than is necessary and the fuel consumption increases.
Minimum fuel consumption rate
The minimum fuel consumption rate shown by the engine performance curve is when the throttle valve is fully opened and it is not always equal to the fuel consumption in the normally used range.
2. Vehicle weight difference
As the vehicle weight is greater, fuel consumption increases. The increase in vehicle weight does not greatly affect the fuel consumption while driving at a constant speed on a fl at road. But, when repetitively starting, accelerating and climbing up hill, the vehicle weight largely affects the fuel consumption.
3. Difference in style (aerodynamics)
The air resistance increases against the square of the vehicle speed. Therefore, in low-speed driving, the air resistance does not affect the fuel consumption, but in high-speed driving, it largely affects the fuel consumption.
The air resistance is in proportion to the multiplication of the Cd value of the frontal projected area. In other words, even if the Cd value is small, the frontal projected area is large, so the air resistance becomes large. Therefore, even if the Cd value in a large vehicle is small, the air resistance is not always small. In short, it cannot be said that the fuel consumption will decrease.
Compared to What?
4. Difference in transmission and gear ratio
• Generally, when the gear ratio is small, engine speed is kept low and the throttle valve opening becomes large to drive with the equal power. As a result, the engine pumping loss decreases and fuel consumption decreases.
• When comparing a manual transmission vehicle (hereafter referred to as an M/T vehicle) with an automatic transmission vehicle (hereafter referred to as an
A/T vehicle), in low-speed driving, the fuel consumption of an A/T vehicle is larger than that of an M/T vehicle due to torque converter slip. On the other hand, in high speed driving where the lock-up functions, the fuel consumption in both vehicles becomes equal.
Pumping loss
Pumping loss is the resistance when the engine sucks in the air. When the throttle valve opening is small, pumping loss is large.
5. Tire difference
The reason why the tire affects the fuel consumption is that the majority of the rolling resistance during running resistance is in the tire. The tire rolling resistance varies depending on the air pressure or tire type.
6. Difference between the actual vehicle and the catalogue data
The fuel consumption in the catalogue is measured under a specified condition. Therefore, in many cases, the running conditions are different from those performed by customers, the fuel consumption increases depending on the conditions; average running speed is low, the ratio of vehicle stoppage is high, sudden acceleration is performed, etc.
• Causes due to roads and surroundings
Temperature and moisture are different Wind influences Speed changes considerably due to slope, inclination and humps on the roads
• Cause on the vehicle side
Vehicle weight is different
Keeping the throttle opening constant is difficult even during constant running Change with over time (Vehicle friction change, carbon accumulation)

Malfunction areas in Turbocharger/ Supercharger
Due to insufficient boost pressure, insufficient power is felt when vehicle starts or a heavy load is applied.
When sudden accelerating without load, diesel smoke level inspection is normal (diesel engine) Intake system
Malfunction areas in  Intake system
When a heavy load is applied and the engine speed is high, there is a shortage of intake air and insufficient power is felt.
Feeling that engine speed has hit its peak, however engine speed does not increase.
When sudden accelerating without load, a lot of black smoke is exhausted in the diesel smoke level inspection (diesel engine)

Malfunction areas in  EGR system

Due to excessive EGR volume, insufficient power is felt when vehicle starts or a heavy load is applied.
When sudden accelerating without a load, more black smoke is exhausted in the diesel smoke level inspection (diesel engine)
Malfunction areas in  Exhaust system
Due to clogging in exhaust system, there is a shortage of intake air, and insufficient power is felt when a heavy load is applied and there the engine speed is high.
When driving with the throttle valve fully open in 1st or 2nd gear, the maximum speed is lower.

Malfunction areas in  Cooling system

After driving for a while with a heavy load applied and engine speed high, insufficient power is felt.
The water temperature indicator indicates high temperature. Knocking is often accompanied.
In the case of diesel engine, even if overheat occurs, insufficient power is not immediately felt. Until when a malfunction in the cylinder head gasket,
piston, etc. occurs, insufficient power is not felt, so it is necessary to pay attention (diesel engine).

Malfunction areas in  Fuel system

Due to fuel supply shortage, insufficient power is felt when a heavy load is applied or the engine speed is high.
When driving with the throttle valve fully open in 1st or 2nd gear, the maximum speed is lower.
Engine stall also may occur.

Malfunction areas in  Injection timing

If injection timing advances, insufficient power is felt when vehicle starts or a heavy load is applied and diesel knocking sound is loud (diesel engine).
When sudden accelerating without a load, black smoke volume is large in the diesel smoke level inspection (diesel engine)

Malfunction areas in  Injection volume

Due to injection volume shortage, insufficient power is felt in the heavy load range, from low speed to high speed (diesel engine).
When sudden accelerating without a load, diesel smoke level inspection is small (diesel engine)
Due to injection volume shortage, insufficient power is felt in the heavy load range, from low speed to high speed (diesel engine).
When sudden accelerating without a load, diesel smoke level inspection is small (diesel engine)

Malfunction areas in  Compression pressure

Insufficient power is felt in all ranges from the starting acceleration.

Malfunction areas in  Automatic transmission

Due to clutch or brake slip, vehicle speed does not follow the engine speed increase.
The symptom significantly appears when running with half throttle.
Due to shifting point failure, both engine speed increase and vehicle speed increase is retard.
Due to the lock up clutch full-time operation, both engine speed increase and vehicle speed increase is retarded

Engine System
• When fully depressing the accelerator pedal, whether the throttle valve fully opens or not
• Whether the amount of coolant and engine oil is good or not, whether the drive belt tension is good or not (overheat is suspected)
• Whether rough idling exists or not (compression pressure drop in a specific cylinder is suspected)
• Whether the air cleaner element has dirt or not (clog in intake system is suspected)
• Whether the diesel smoke level when sudden accelerating without load is good or not (diesel engine only)
• Whether no load maximum speed is good or not (diesel engine only)

Drive train System
• Whether the clutch slip exists or not
• The amount of ATF is good or not (AT slip is suspected)
• Whether stall speed is good or not (AT slip and torque converter failure are suspected)
Brake System
• Whether the brake drag exists or not
Others System
• Whether the fuel sedimenter indicator operates or not