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Feb 13 2019

What is A Knock Sensor&Troubleshooting Guide

I Introduction

The knock sensor is an indispensable important component in the electronic control system of the engine. Its function is to detect whether the engine has knocking phenomenon and send the signal to the engine ECU.

This article will mainly introduce the definition, types, function, working principle, bad symptoms of knock sensors and detection methods of bad knock sensors. Also, the detailed detection steps of several specific models of vehicles are included in the part of troubleshooting guide.

What Is A Knock Sensor? (Detonation, Pinging)

Catalog

I Introduction

II What is Knocking?

 2.1 The Explanation of Knocking

 2.2 The Hazards of Knocking

 2.3 Measures to Prevent Knocking

III What is A Knock Sensor?

 3.1 The Explanation of Knock Sensor

 3.2 Structure, Installation Location and Terminal

 3.3 Mechanism of Engine Knock Control

IV Types of Knock Sensor

 4.1 Magnetostrictive Knock Sensor

 4.2 Piezoelectric Knock Sensor

V Symptoms of Faulty Knock Sensor

VI Troubleshooting Guide of Knock Sensor

 6.1 Specific Detection Steps of Knock Sensor Failure

 6.2 Detection of Resonant Piezoelectric Knock Sensor

 6.3 Diagnose Engine Failure with Knock Sensor

VII Knock Sensor Failure Detection For Specific Vehicle Models

 7.1 Toyota Corolla Models

 7.2 Jetta and Santana Models

 7.3 Summary

II What is Knocking?

2.1 The Explanation of Knocking

In gasoline engines, spark plugs are used to ignite the air-fuel mixture, so that the flame is continuously propagated in the air-fuel mixture for combustion. During the propagation of the flame, if the pressure rises abnormally, the mixed gas in some parts will burn on its own without waiting for the flame to reach, causing instantaneous explosive combustion. This phenomenon is called knock.

The combustion of the engine is very complicated, so it requires a fairly accurate design and control. A little control error or abnormality will cause abnormal combustion, and "knock" is an abnormal combustion. Simply put, knocking is an abnormal pressure in the combustion chamber caused by abnormal combustion.

Engine Knocking

Figure1. Engine Knocking

2.2 The Hazards of Knocking

(1) Loud noise (sharp knocking sound).

(2) Strong knocking reduces the power of the engine, the temperature of the engine rises sharply, and the heat taken away by the cooling water increases, thereby reducing the thermal efficiency.

(3) The impulse pressure wave of abnormal combustion impulses and aggravates the load of engine parts, which increases the stress and easily damages.

(4) Overheating of the cylinder will aggravate the carbon deposits to form local overheating, and may even make the metal soft, melt or burn.

(5) The engine is unstable and vibrates violently.

Knocking

Figure2. Knocking

2.3 Measures to Prevent Knocking

(1) High compression ratio is one of the conditions for knocking, so it is necessary to regularly remove carbon deposits in the combustion chamber and the top of the piston. Deformation of the end surface of the cylinder head should be replaced immediately after overhaul. Planing the end faces often increases the compression ratio.

(2) Eliminate carbon deposits in the exhaust valve, piston crown and combustion chamber, and eliminate possible hot spots of final combustion.

(3) Use gasoline that meets the compression ratio of the engine. The octane component in gasoline can suppress knocking, and gasoline with a low octane value can cause knocking. The marking of gasoline can be found in the instruction manual of the car.

(4) The function of the cooling system is normal. If the water temperature is too high or the pot is frequently "opened", the obstacles must be removed, otherwise it will easily cause knocking.

(5) Premature ignition may cause knocking too early. The ignition advance angle should be adjusted according to the instruction or the ignition timing symbol of the flywheel, or it has the right to knock slightly when it is adjusted to low speed, high gear, and refueling.

(6) When the engine requires a large load (climbing or acceleration) at a low speed, it should be shifted to a low gear in a timely manner, and do not cause knocking due to high speed.

In order to enhance the engine output power and reduce fuel consumption, modern cars generally implement ignition closed-loop control, and the ignition closed-loop feedback signal is completed by the knock sensor. In this way, the engine can control the ignition advance more accurately, so that it can better control the maximum output of the engine and save fuel.

III What is A Knock Sensor?

3.1 The Explanation of Knock Sensor

Knock sensors are AC signal generators, but they are very different from most other automotive AC signal generators. In addition to detecting the speed and position of the rotating shaft like magnetoelectric crankshaft and camshaft position sensors, they also detect vibration or mechanical pressure. Unlike stators and magnetoresistors, they are usually piezoelectric devices. They are made of special materials that can sense mechanical pressure or vibration (for example, AC voltage can be generated when the engine knocks).

Premature ignition, poor exhaust gas recirculation, and engine knock caused by low-grade fuel can cause engine damage. The knock sensor provides a knock signal to the computer (some through the control module PCM), so that the computer can readjust the ignition timing to prevent further knocking. They actually act as an "oxygen sensor" for the ignition timing feedback control cycle.

Knock Sensor

Figure3. Knock Sensor

3.2 Structure, Installation Location and Terminal

(1) Structure and installation location

The knock sensor is installed on the engine block or cylinder head (as shown in the figure below) to detect abnormal combustion. Once the occurrence of knocking is detected, the ECU will gradually delay ignition until the knocking is eliminated; after knocking is eliminated for a period of time, if knocking does not occur again, the ECU will gradually restore the original ignition timing, namely, the closed loop control of it. Therefore, the knock sensor is a dedicated sensor for the ECU to perform closed-loop control of the ignition timing.

Location of Knock Sensor

Figure4. Location of the Knock Sensor

When there is a fault in the knock sensor, the above-mentioned closed-loop control fails. In order to avoid the damage caused by knocking to the engine, the ECU will store the corresponding fault code and delay the ignition timing of each cylinder by a certain value (Toyota delays 8 °; Volkswagen The car is delayed by 15 °). At this time, the power and economy of the engine will decrease.

Structure of a Knock Sensor

Figure5. Structure of a Knock Sensor

(2) Terminal

Because the sensor shell is well grounded, it has only one output signal line, which is connected to the control computer ECU through a wire connector, and its signal is often expressed as "KNK".

In order to detect engine knock more accurately, the engine is usually equipped with two knock sensors, which are installed in two parts of the cylinder, and correspondingly send a voltage signal to the control computer, namely "KNK1" and "KNK2".

The Circuit of Knock Sensor

Figure6. The Circuit of Knock Sensor

3.3 Mechanism of Engine Knock Control

(1) The Relationship Between Knocking and Ignition Advance

There is a close relationship between knocking and ignition advance. The greater the ignition advance angle, the greater the maximum pressure of combustion, and the easier it is to knock. Experiments show that the ignition moment when the engine emits the maximum torque is near the moment when the knocking ignition starts. For mechanically controlled ignition, ordinary electronic ignition, or electronically controlled electronic ignition (no knock feedback, ie, an ignition system without a knock sensor system), in order to prevent it from knocking under the worst conditions, its ignition advance angle is set within the range of the knocking edge, so that it is far away from the knocking limit and there is a large margin. This will inevitably reduce the engine power, reduce the engine output power, and increase fuel consumption.

The Relationship Diagram

Figure7. The Relationship Diagram

(2) Knock Control Mechanism

The computer controls the closed-loop ignition system. The knock sensor installed on the body detects the knock strength of the engine. When the knock sensor detects the body knock, the electronically controlled computer automatically reduces the ignition advance angle gradually until the engine does not produce knock. When the engine does not knock, the current ignition advance angle is maintained for a certain period of time. During this period, if knocking occurs, the ignition advance angle is also reduced; if there is no knocking during this time, the electronic control computer automatically increases the ignition advance angle gradually until the engine knocks. In this way, the control computer always keeps the engine working on the edge of knocking, thereby increasing engine power and reducing fuel consumption.

IV Types of Knock Sensor

Knock sensors can be divided into several types, including magnetostrictive type, semiconductor piezoelectric type and spark plug metal pad type (less applications), among which piezoelectric type knock sensors are divided into resonant piezoelectric knock sensors and non-resonant piezoelectric Knock sensor.

There are two common knock sensors, one is a magnetostrictive knock sensor and the other is a piezoelectric knock sensor.

The Mind Map of Knock Sensors Types

Figure8. The Mind Map of Knock Sensors Types

4.1 Magnetostrictive Knock Sensor

The shape and structure of the magnetostrictive knock sensor are shown in the following figure. There are permanent magnets, a ferromagnetic core excited by the permanent magnet, and coils around the core.

The Shape and Structure of Magnetostrictive Knock Sensor

Figure9. The Shape and Structure of Magnetostrictive Knock Sensor

How it works:

When the cylinder block of the engine vibrates, the sensor resonates with the engine at around 7kHz, and the magnetic permeability of the ferromagnetic material core changes, so that the magnetic flux density of the permanent magnet passing through the core also changes, which causes Generate an induced electromotive force and input this electrical signal to the ECU.

The Composition of Magnetostrictive knock sensor

Figure10. The Composition of Magnetostrictive knock sensor

4.2 Piezoelectric Knock Sensor

The structure of the piezoelectric knock sensor is shown in the figure below. This kind of sensor uses the piezoelectric effect of crystal or ceramic polycrystal to work, and also uses the piezoelectric resistance effect of doped silicon. The housing of the sensor is equipped with piezoelectric elements, counterweights and wires.

The Structure of Piezoelectric Knock Sensor

Figure11. The Structure of Piezoelectric Knock Sensor

How it works:

When the cylinder block of the engine vibrates and the vibration is transmitted to the sensor housing, relative motion occurs between the housing and the weight, and the pressure on the piezoelectric element sandwiched between the two changes, thereby generating a voltage. The ECU detects this voltage and judges the knocking intensity according to its value.

V Symptoms of Faulty Knock Sensor

(1) When the engine is working, the engine will knock due to excessive ignition timing advance (ignition advance angle), engine load, temperature and fuel quality. When knocking occurs, due to gas combustion before the piston moves to the top dead center, it may produce noise and reduce the power of the engine, and can damage the mechanical parts of the engine.

(2) If the knock sensor is damaged, the engine control unit (ECU) cannot monitor the degree of knocking. When the engine control unit detects the knocking of the engine through the knock sensor, the ignition advance angle will be reduced, thereby erroneously judging that knocking does not occur. In this case, the engine control unit will increase the ignition advance angle, causing the engine to violently shake due to knocking.

(3) After the knock sensor is broken, the ignition time will be automatically delayed to prevent engine knock. Therefore, the engine will be in the working state with delayed ignition.

(4) Engine fuel consumption will increase, and combustion energy rate as well as engine power will decrease.

VI Troubleshooting Guide of Knock Sensor

6.1 Specific Detection Steps of Knock Sensor Failure

6.1.1 Fault description

If the knock sensor fails, fault code P0324 (knock control system failure) and fault code P0325 (knock sensor failure) will be generated (the following table).

Fault Code

Detection Strategy

Fault code setting conditions(Control Strategy)

Fault Location

P0324

Knock control system failure

①not lower than 6000r/min

②Certain load state

③Either end of the sensor signal wire is Grounded

①Sensor circuit

②Sensor

③Engine control unit

P0325

Knock sensor fault

①not lower than 6000r/min

②Certain load state

③The sensor signal line is disconnected

The knock sensor is to provide knock information, used to correct the ignition timing, and realize the closed-loop control of detonation.

When knocking is about to occur, the knocking signal point cannot be provided, and the computer cannot receive the signal "peak value". Also, the ignition advance angle cannot be reduced to cause knocking.

6.1.2 Knock sensor circuit

The feedback signal of the knock sensor (KS) to the ECM can achieve the most optimal ECM control of ignition timing, the best performance of the ignition system, as well as preventing the engine from being potentially knocked damage. The KS sensor is located on the cylinder block below the intake manifold and the AC signal voltage generated by the KS sensor varies with the vibration level of the engine during operation.

The engine control module adjusts the spark timing based on the amplitude and frequency of the KS sensor signal. The ECM receives the signals from terminals 1 and 2 of the KS sensor harness connector EN08 through the ECM harness connector EN72 terminals 19 and 20 (below).

The Circuit of Knock Sensor

Figure12. The Circuit of Knock Sensor

6.1.3 Diagnostic steps

If the knock sensor malfunctions, follow the steps below to conduct a diagnostic check.

Step 1: Basic inspection

① Check whether the KS sensor is physically damaged.

② Check whether the KS sensor is installed correctly. If the torque is too tight or too loose, the diagnosis code will be set.

③ Check whether there are any burrs, casting flash and foreign objects on the mounting surface of the KS sensor.

④ The knock sensor must be kept away from hoses, brackets and engine wiring.

If it is not normal, deal with the faulty part and go to the eighth step; if it is normal, go to the next step.

Step 2: Read engine data on the fault diagnosis instrument (engine speed)

① Connect the fault diagnosis instrument to the diagnosis interface.

② Turn the ignition switch to the "ON" position.

③ Select "Engine" / "Read Data Stream" / "Knock Sensor Signal 1".

④ Start the engine and bring it to normal operating temperature.

⑤ The road test vehicle reads the engine speed data (standard value: normal data) displayed by the fault diagnosis instrument.

If it is not normal, go to the third step; if it is normal, go to the next step.

Step 3: Check the sensor

① Turn the ignition switch to the "OFF" position.

② Disconnect the knock sensor harness connector EN48.

③ Measure the resistance value of knock sensor (standard resistance value: 49kΩ at 20 ℃)

④ Connect the knock sensor harness connector EN48.

If the resistance value is abnormal, replace the knock sensor and go to step eight; if it is normal, go to the next step.

Step 4: Check the sensor terminal 1 line

① Turn the ignition switch to the "OFF" position.

② Disconnect the knock sensor harness connector EN48.

③ Disconnect the ECM harness connector EN44.

④ Measure the resistance between the No. 1 terminal of the knock sensor harness connector EN48 and the No. 30 terminal of the ECM harness connector EN44, and check whether there is a disconnection in the line.

⑤ Measure the resistance value between the No. 1 terminal of the knock sensor harness connector EN48 and reliable ground, and check whether there is a short circuit to ground in the line.

⑥ Measure the voltage value between the No. 1 terminal of the knock sensor harness connector EN48 and reliable ground, and check whether there is a short circuit to the power supply in the line.

The above measurement parameters are shown in the table below.

Measurement items

Standard Value

EN48(1) - EN44(30) Resistance

Less than 1Ω

EN48(1) - Reliable grounding resistance

10Ω or higher

EN48(1) - Reliable ground voltage

0V

If it does not meet the specified value, deal with the faulty part and go to step eight; if it does, go to the next step.

Step 5: Check the sensor terminal 2 line

① Turn the ignition switch to the "OFF" position.

② Disconnect the knock sensor harness connector EN48.

③ Disconnect the ECM harness connector EN44.

④ Measure the resistance between the No. 2 terminal of the knock sensor harness connector EN48 and the No. 31 terminal of the ECM harness connector EN44, and check whether there is a disconnection in the line.

⑤ Measure the resistance value between the No. 2 terminal of the knock sensor harness connector EN48 and reliable grounding, and check whether there is a short circuit to ground on the line.

⑥ Measure the voltage value between the No. 2 terminal of the knock sensor harness connector EN48 and the reliable ground, and check whether the circuit has a short circuit to the power supply.

The above measurement parameters are shown in the table below.

Measurement items

Standard Value

EN48(2) - EN44(31) Resistance

Less than 1Ω

EN48(2) - Reliable grounding resistance

10Ω or higher

EN48(2) - Reliable ground voltage

0V

If it does not meet the specified value, deal with the faulty part and go to step eight; if it does, go to the next step.

Step 6: Check the ECM power circuit

① Check whether the ECM power circuit is normal.

② Check whether the ECM grounding circuit is normal.

If it is not normal, deal with the faulty part; if it is normal, go to the next step.

Step 7: Replace ECM

Step 8: Use the fault diagnosis instrument to confirm whether the fault code is stored again

① Connect the fault diagnosis instrument to the diagnostic test interface.

② Turn the ignition switch to the "ON" position.

③ Clear the fault code.

④ Start the engine and run it at idle speed for at least 5 minutes.

⑤ At least 10 minutes of road test vehicles.

⑥ Read the fault code of the control system again to confirm that the system has no fault code output.

If there is no fault code output, it is an intermittent fault.

Step 9: Troubleshoot the problem

 Knock Sensor Circuit Test

Figure.13 Knock Sensor Circuit Test

6.2 Detection of Resonant Piezoelectric Knock Sensor

(1) On-board Detection

According to the knock control principle, when the engine knocks, the engine will delay the ignition advance angle until the engine does not knock; when the engine does not knock, the engine will increase the ignition advance angle until the engine knocks. Therefore, when we strike the engine block with a wrench or other metal objects, the engine speed should immediately decrease and then resume immediately. Or we use a timing gun to observe the ignition advance angle. At this time, the ignition advance should be immediately postponed backward, and then advanced again. This phenomenon indicates that the knock sensor is working, and there is basically no problem with the knock sensor and its circuit; otherwise, it indicates that the knock sensor or the circuit is faulty, and the knock sensor or the circuit should be checked for problems.

(2) Departure Detection

If the knock sensor is found to be faulty during the vehicle inspection, the vehicle should be checked for departure. Knock sensors generally have three wires, two of which are knock signal wires and one is shielded wire to prevent knock signals from being disturbed. When testing, if we have a multimeter, we should turn the knob to the millivolt voltage range, and directly hit the knock sensor base with a wrench or other objects. It should have a voltage display, which is roughly 400mV. If the voltage is in this range, it means that it is basically intact, otherwise the line between the sensor and the computer should be checked. If no voltage is generated at all, the sensor has been damaged and should be checked according to the circuit diagram.

However, testing with a multimeter is generally less accurate and less intuitive, and inspection with an oscilloscope will be more intuitive and accurate. When we strike the resonance plate with a hard object, the oscilloscope will output a clear and intuitive oscillation waveform, which shows that the sensor is intact. If there is no waveform output or the output is extremely weak, the sensor is damaged and the knock sensor should be replaced.

Related Post: How to test a capacitor with a multimeter?

(3) Note

When the knock sensor is damaged, the circuit is short-circuited, the circuit is disconnected, the tightening screws are not tightened, the cylinder work is seriously unbalanced, and the engine and frame are connected to the foot glue damage, etc. ", The engine fault warning light is on, we can use the decoder to read out the fault code, but the" knock sensor signal is not good "does not necessarily mean that the knock sensor or circuit has a problem, we should analyze the specific problem, not based Self-diagnosis results act blindly.

Bad Knock Sensor Pattern

Figure14. Bad Knock Sensor Pattern

6.3 Diagnose Engine Failure with Knock Sensor

The knock sensor responds to whether the engine body is knocking. It is a feedback value. The computer judges whether it is good or bad based on whether its feedback signal is within the normal range. If it has been out of range, the computer self-diagnosis system will set a fault code. And whether the engine knocks is a comprehensive manifestation of the engine's work, which includes "true knocking" and "false knocking".

"True knocking":

"True Knocking" refers to abnormal combustion of the engine. The body produces strong vibrations, mainly due to the crank signal and the ignition signal. The engine water temperature is too high and the mixed gas burns itself before the central flame reaches the center. The intake and exhaust and ignition timing are all disordered, the three-way catalyst is seriously blocked, and the exhaust is blocked and accelerated rapidly, resulting in a strong vibration of the engine.

"False knocking":

"False knocking" refers to the vibration of other parts of the machine body causing the knock sensor to react incorrectly to the knocking signal. It mainly refers to the serious imbalance of the cylinder work leading to the severe jitter of the engine, the damage of the rubber of the engine lead to a direct hard collision between the engine and the frame, and the loose sensor lock tightening screws cause severe vibration of the knock sensor, abnormal acceleration of the engine caused by intermittent misfire due to rapid acceleration, etc.

Therefore, the knock signal is related to its own line on the one hand, and it is also related to the "true knocking" and "false knocking" of the engine. According to the self-diagnosis results of the engine, we can analyze the failure. On the one hand, we can diagnose itself, and we can also diagnose the failure of other parts of the engine. This is something we should pay attention to and deserves serious consideration.

Knock Sensor

Figure15. Knock Sensor

It is precisely because the knock sensor feedbacks the comprehensive working conditions of the engine, so it reacts with the oxygen sensor to many fault information associated with it. This is an important basis for our analysis to judge whether other parts of the engine are abnormal. According to the general car repair The experience sums up, the meaning and diagnosis method of the "knock sensor signal is bad" include:

1) When the engine is idling, the ignition advance angle of a general car engine changes around 10 degrees. The range of the knock sensor adjustment is generally plus or minus 4 degrees. When we use the ignition timing gun to observe the ignition advance angle, if the ignition advance angle is fixed. If it changes, it means that the knock signal circuit is bad. The engine control ignition closed loop has stopped adjusting the ignition advance, then we should focus on checking the knock sensor for damage, short circuit, and open circuit.

2) When the ignition advance angle oscillates violently, it may be that the abnormal vibration of the body leads to abnormal feedback of the knock sensor. We should focus on checking:

  1. a) The knock sensor fixing screw is loose.
  2. b) The crank angle signal or judging cylinder signal is confusing.
  3. c) The foot rubber connecting the engine and the frame is worn.
  4. d) The cylinder work is seriously unbalanced.
  5. e) The engine water temperature is too high.
  6. f) Poor ignition, such as intermittent misfire.
  7. g) Timing belt jump teeth and wrong assembly.
  8. h) The three-way catalytic reactor is seriously blocked.

VII Knock Sensor Failure Detection For Specific Vehicle Models

7.1 Toyota Corolla Models

Special note: The Toyota Corolla 1ZR-FE engine uses a piezoelectric knock sensor, and its working circuit is as shown in the figure below. When fault code P0327 (knock sensor output voltage is lower than 0.5V) and P0328 (knock sensor output voltage higher than 4.5V) appear, the following inspection steps are required.

Working circuit of knock sensor of Toyota Corolla 1ZR-FE engine

Figure17. Working Circuit of Knock Sensor of Toyota Corolla 1ZR-FE Engine

Detection steps:

(1) Read the feedback data of knock sensor.

(2) Check the KNK1 voltage provided by the ECU to disconnect the knock sensor connector, as shown in the figure below.

(3) Check the knock sensor.

(4) Check the wiring between the knock sensor and the ECU.

Shape of the connector of the knock sensor harness side

Figure18. Shape of the Connector of the Knock Sensor Harness Side

Measure the Resistance of the Knock Sensor

Figure19. Measure the Resistance of the Knock Sensor

7.2 Jetta and Santana Models

The knock sensor circuits and connectors of Jetta and Santana models are shown in the figure.

Knock sensor circuit and connector for Jetta and Santana models

Figure20. Knock Sensor Circuit and Connector for Jetta and Santana Models

Detection steps:

(1) Measuring the resistance of the sensor

Disconnect the knock sensor connector and use a multimeter to measure the resistance between the relevant terminals of the sensor. The measurement result should meet the requirements of the table below, otherwise, replace the knock sensor.

(2) Check the wiring between the knock sensor and the ECU

Disconnect the ECU connector and measure the resistance between the sensor connector and the corresponding terminal of the ECU connector with a multimeter,

Should comply with the following table, otherwise, repair or replace the harness or connector.

Test items

Test conditions

Detection Parts

Standard Value

 

The resistor of knock sensor

Disconnect the ignition switch, disconnect the sensor connector

Terminal 1-Terminal 2

 

>1MΩ

Terminal 1-Terminal 3

Terminal 2-Terminal 3

Test items

Test conditions

Detection Parts

Standard Value

Sensor signal positive line

Disconnect the ECU connector, disconnect the sensor connector

ECU connector terminal 60-sensor connector terminal 1

 

 

<0.5Ω

Sensor signal negative line

Disconnect the ECU connector, disconnect the sensor connector

ECU connector terminal 68-sensor connector terminal 1

Sensor shielded wire

Disconnect the ECU connector, disconnect the sensor connector

ECU connector terminal 67-sensor connector terminal 2

 

<0.5Ω

Engine grounding point (next to ECU)-sensor connector terminal 3

 

<0.5Ω

Jetta, Santana models knock sensor measurement standards

7.3 Summary

The knock sensor is used to detect the knock condition of the engine, and the ECU uses its signal to perform closed-loop control of the ignition timing. The knock sensor generally judges the engine's knocking condition by detecting the vibration state of the engine block or head. According to the different working principles, there are two types: piezoelectric and magnetostrictive.

The inspection contents of the knock sensor generally include: reading the feedback data of the knock sensor, checking the operating voltage provided by the ECU, checking the wiring between the knock sensor and the ECU, measuring the resistance of the sensor, etc.

8.1 Question

 The important parameters in a gasoline engine that can be controlled are

  1. a) air-fuel ratio
  2. b) mixture distribution between cylinders
  3. c) ignition timing
  4. d) all of the mentioned

8.2 Answer

Answer: d

Explanation: The important parameters in a gasoline engine that can be controlled are

  1. a) air-fuel ratio
  2. b) mixture distribution between cylinders
  3. c) ignition timing
  4. d) injection timing of the fuel
  5. e) idle speed.

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