LEARNING OUTCOME 2

Fuel Injection System Layout

A typical fuel injection system, especially in modern vehicles, follows this general layout:

1. Fuel Tank:
   • Stores the fuel.
2. Electric Fuel Pump:
   • Located in or near the fuel tank, it delivers fuel under pressure.
3. Fuel Filter:
   • Removes impurities from the fuel.
4. Fuel Lines:
   • Carry fuel to the engine.
5. Fuel Rail:
   • Distributes fuel to the individual fuel injectors.
6. Fuel Injectors:
   • Spray fuel into the intake manifold or directly into the cylinders.
7. Air Intake System:
   • Includes the air filter, throttle body, and intake manifold.
8. Sensors:
   • MAF/MAP sensors, O2 sensors, temperature sensors, etc., provide data to the ECU.
9. Electronic Control Unit (ECU):
   • Processes sensor data and controls the fuel injectors.
10. Exhaust System:
    • Including the lambda sensor and sometimes the EGR valve.

Safety Precautions

Fuel Handling:

• Work in a well-ventilated area.
• No smoking or open flames.
• Clean up fuel spills immediately.
• Relieve fuel pressure before disconnecting lines.
• Wear eye and skin protection.

Electrical Safety:

• Disconnect the battery.
• Use insulated tools.
• Handle components carefully.

Fuel Management

Stoichiometric Ratio:

• The ideal air/fuel ratio for complete combustion.
• For gasoline, it's approximately 14.7:1 (14.7 parts air to 1 part fuel).
• This ratio optimizes emissions and fuel efficiency.

Air/Fuel Mixture:

• Rich Mixture:
  • Excess fuel (less air).
  • Can increase power but increases emissions.
• Lean Mixture:
  • Excess air (less fuel).
  • Can improve fuel efficiency but can increase NOx emissions and potentially damage the engine.

Lambda Sensor (Oxygen Sensor):

• Measures the oxygen content in the exhaust gases.
• Provides feedback to the ECU to adjust the air/fuel mixture.
• Lambda (λ) is a value that indicates the air/fuel ratio relative to the stoichiometric ratio:
  • λ = 1: Stoichiometric ratio.
  • λ > 1: Lean mixture.
  • λ < 1: Rich mixture.

EGR (Exhaust Gas Recirculation):

• Recirculates a portion of the exhaust gases back into the intake manifold.
• Reduces NOx emissions by lowering combustion temperatures.
• The ECU controls the EGR valve to regulate the amount of exhaust gas recirculated.

Fuel Injection System Types

1. Pressure-Based/Sensed Systems:

• These systems rely on fuel pressure differentials to control fuel delivery.
• They often use mechanical components to regulate fuel flow.
• Older systems, like some early mechanical injection systems, fell into this category.

2. Continuous Injection Systems:

• Fuel is continuously sprayed into the intake manifold, regardless of the engine's intake stroke.
• The amount of fuel delivered is varied by controlling the fuel pressure.
• K-Jetronic:
  • A continuous, mechanical fuel injection system.
  • Uses a fuel distributor and air-flow sensor to control fuel delivery.
  • Relies on fuel pressure and mechanical linkages.
• KE-Jetronic:
  • An electronically controlled version of K-Jetronic.
  • Adds electronic control to the fuel pressure regulator, allowing for more precise fuel metering.

3. Intermittent Injection Systems:

• Fuel is injected in pulses, timed to coincide with the engine's intake stroke.
• This allows for more precise fuel control and better fuel economy.
• L-Jetronic:
  • An electronic, multi-point fuel injection system.
  • Uses a mass airflow (MAF) sensor to measure intake air volume.
  • Electronically controlled injectors deliver fuel intermittently.
• LE-Jetronic:
  • A simplified version of the L-Jetronic system.
• LH-Jetronic:
  • Uses a hot-wire MAF sensor for more accurate air measurement.
• LU-Jetronic:
  • This is a less common variation, that had some variations in the sensors used.
• Motronic:
  • A combined fuel injection and ignition control system.
  • Integrates fuel injection, ignition timing, and other engine management functions.
  • Available in many variations.
• Mono-Jetronic:
  • A single-point fuel injection system (throttle body injection).
  • Uses a single injector located in the throttle body.
  • Simpler and less expensive than multi-point systems.

4. Modern Electronic Systems:

• Common Rail Systems:
  • Used primarily in diesel engines.
  • Fuel is stored in a common rail at high pressure.
  • Electronically controlled injectors deliver precise amounts of fuel directly into the cylinders.
  • Extremely high pressure systems.
• Direct Injection Systems (Gasoline Direct Injection - GDI):
  • Fuel is injected directly into the combustion chamber, rather than the intake manifold.
  • Allows for precise fuel control, improved fuel economy, and increased power.
  • This is a pressure based, and intermittent system.
  • Can create issues with carbon buildup on the intake valves.

Differences:

• Mechanical systems (like K-Jetronic) rely on mechanical components and fuel pressure.
• Electronic systems (like L-Jetronic, Motronic, and GDI) use sensors, ECUs, and electrically controlled injectors.
• Continuous injection systems deliver fuel constantly, while intermittent systems deliver fuel in pulses.
• Direct injection injects fuel directly into the cylinder, and indirect injection injects fuel into the intake manifold.

Checking Components/System Functionality

1. Fuel Pressure Test:

• Connect a fuel pressure gauge to the fuel rail.
• Check the fuel pressure against the manufacturer's specifications.
• Observe if the pressure holds steady or drops.
• This checks the fuel pump, pressure regulator, and fuel lines.

2. Fuel Injector Testing:

• Pulse Testing: Use a noid light or oscilloscope to check for electrical pulses to the injectors. This verifies the ECU's control of the injectors.
• Resistance Testing: Use a multimeter to check the resistance of the injector coils. This identifies open or shorted injectors.
• Spray Pattern Testing: Remove the injectors and observe the spray pattern. A good injector will have a fine, even mist.
• Volume testing: measure the amount of fuel each injector delivers over a set amount of time.

3. Sensor Testing:

• MAF/MAP Sensor: Use a scan tool to monitor sensor readings. Check for accurate readings and response to changes in airflow or pressure.
• O2 Sensor: Use a scan tool or multimeter to check sensor voltage and response time. Look for switching between rich and lean readings.
• Temperature Sensors: Use a multimeter to check sensor resistance at different temperatures. Compare readings to manufacturer's specifications.
• Position Sensors (CKP/CMP): Use a scan tool or oscilloscope to check sensor signals. Look for consistent and accurate signals.
• Compare scan tool live data to known good values.

4. Fuel Pump Testing:

• Check fuel pump operation by listening for the pump to run when the ignition is turned on.
• Check fuel pump amperage draw.
• Check fuel pump voltage.

5. Wiring and Connections:

• Visually inspect wiring for damage, corrosion, or loose connections.
• Use a multimeter to check for continuity and voltage at connectors.

6. ECU Diagnostics:

• Use a scan tool to read diagnostic trouble codes (DTCs).
• Monitor live data from sensors and actuators.
• Perform actuator tests using the scan tool.

7. Exhaust System:

• Visual inspection for leaks.
• Backpressure testing.

8. Air Intake System:

• Check for air leaks.
• Inspect air filter condition.

Common Faults

Fuel Pump Failure:

• Causes: Worn pump, electrical issues, contaminated fuel.
• Symptoms: No fuel delivery, low fuel pressure, engine stalling.

Clogged Fuel Filter:

• Causes: Contaminated fuel.
• Symptoms: Low fuel pressure, poor engine performance, engine stalling.

Faulty Fuel Injectors:

• Causes: Clogged injectors, electrical failures, worn seals.
• Symptoms: Misfires, poor idle, reduced power, increased fuel consumption.

Faulty Sensors:

• Causes: Electrical failures, contamination, wear and tear.
• Symptoms: Poor engine performance, increased emissions, inaccurate sensor readings.

Wiring and Connection Problems:

• Causes: Corrosion, damage, loose connections.
• Symptoms: Intermittent problems, sensor failures, actuator failures.

Vacuum Leaks:

• Causes: cracked hoses, bad gaskets.
• Symptoms: poor idle, increased fuel consumption, rough running.

Faulty Pressure Regulator:

• Causes: Diaphragm failure, spring wear.
• Symptoms: High or low fuel pressure, poor engine performance.

ECU Failures:

• Causes: Electrical surges, water damage, internal component failures.
• Symptoms: Various engine problems, no communication with scan tool.

Lambda Sensor Failure:

• Causes: Contamination, age.
• Symptoms: Poor fuel economy, increased emissions, poor engine performance.

EGR Valve Problems:

• Causes: Carbon buildup, valve failure.
• Symptoms: Rough idle, poor acceleration, increased emissions.

Direct Injection Carbon Buildup:

• Causes: The nature of direct injection.
• Symptoms: Misfires, poor performance, reduced fuel economy.

Computerized Diagnostics Operations

1. Machines and Equipment:

• Scan Tools (Diagnostic Scanners):
  • Handheld or laptop-based devices that connect to the vehicle's OBD-II port.
  • Used to read diagnostic trouble codes (DTCs), monitor live sensor data, perform actuator tests, and reprogram ECUs.
  • Vary in complexity and features, from basic code readers to advanced professional-grade scanners.
• Oscilloscopes:
  • Used to visualize electrical signals from sensors and actuators.
  • Helpful for diagnosing intermittent problems and analyzing signal patterns.
• Multimeters:
  • Essential for checking voltage, resistance, and continuity in electrical circuits.
• Fuel Pressure Testers:
  • Used to measure fuel pressure in the fuel rail.
• Fuel Injector Testers:
  • Used to test the function of the fuel injectors.
• Laptop/PC:
  • For running advanced diagnostic software, accessing online repair information, and reprogramming ECUs.

2. Fault Codes (Diagnostic Trouble Codes - DTCs):

• Codes generated by the ECU when it detects a problem with the fuel injection system or other vehicle systems.
• Each DTC corresponds to a specific fault, such as a faulty sensor, actuator, or wiring issue.
• Scan tools are used to read and interpret DTCs.
• DTCs provide a starting point for diagnosis, but further testing is often required to pinpoint the exact cause of the problem.

3. Internet:

• Online Repair Information:
  • Access to online databases, manufacturer websites, and repair forums for technical information, wiring diagrams, and troubleshooting tips.
• Software Updates:
  • Downloading software updates for scan tools and ECU reprogramming.
• Parts Ordering:
  • Online ordering of replacement parts from suppliers.
• Technical Forums:
  • Access to forums that discuss car repair, and allow for users to ask questions, and to learn from other users.

4. OBD (On-Board Diagnostics):

• OBD-II:
  • A standardized diagnostic system that is mandatory for most modern vehicles.
  • Provides access to diagnostic information through a standardized connector (OBD-II port).
  • Allows technicians to read DTCs, monitor live data, and perform other diagnostic tests.
• Live Data Monitoring:
  • Scan tools can display real-time data from sensors and actuators, allowing technicians to observe how the system is operating.
  • This helps to identify problems that may not trigger DTCs.
• Actuator Tests:
  • Scan tools can be used to activate actuators, such as fuel injectors or EGR valves, to verify their operation.

Computerized Diagnostic Operations Workflow:

1. Connect the scan tool to the OBD-II port.
2. Turn on the ignition.
3. Read and record any DTCs.
4. Use the scan tool to monitor live data from relevant sensors and actuators.
5. Perform actuator tests as needed.
6. Use the internet to research DTCs and find repair information.
7. Use a multimeter or oscilloscope to perform further testing as needed.
8. Replace faulty components.
9. Clear DTCs and retest the system.
10. Verify that the problem is resolved.