CH25 engine performance systems STUDENT VERSION rev

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Chapter 25

Engine Performance Systems

Engine Performance Systems

• Responsible for how the engine runs

• Complete combustion requires:

– Correct amount of air

– Correct amount of fuel

– Mixed in a sealed container

– Shocked with the correct amount of heat

Purpose of the Ignition System

• Generate enough heat to ignite mixture

• Maintain the spark long enough for total combustion of the fuel

• Must deliver the spark to each cylinder to allow combustion to begin at the correct time

Fuel Systems

• Typical fuel supply system includes:

– Fuel tank, lines, filter, and a pump

• A pressure regulator maintains system

pressure

• The pressure generates the spraying force to inject the fuel

Fuel Injection - TBI

Fuel Injection - CPI

Fuel Injection - PFI

Fuel Injection - GDI

Air Induction System

Emission Control Systems

• Reduce pollutants and environmentally

damaging substances

• Smog irritates eyes, nose, and throat

• Formed when HC and NOx are exposed to sunlight

Engine Control Systems

• Primary engine control computer is the ECM or PCM

• Based on input, may command a change

• Monitors system activity for faults

• Linked to several other modules

• Share information on the CAN data bus

On-Board Diagnostic Systems

• OBD I

– Phased in 1988

– Most used flash codes

– DTC represented open, shorted, high resistance,

or outside normal range faults

– Monitored a few systems and had limited DTCs – Often required a specific scan tool

OBD II

• Designed to ensure emissions remain as low

as possible over life of vehicle

• Added monitor functions:

– Catalyst efficiency

– Engine misfire

– Evaporative system

– Secondary air system

– EGR flow rate

OBD II (cont’d)

• Basic data parameters and codes

• Monitors effectiveness of emissions system

• Every part that affects emissions is checked

• MIL illuminated if emissions exceed 150%

of allowable standard for that vehicle

• PCM uses EEPROM for updates

Data Link Connector (DLC)

• Standardized

• Vehicles may have

more than one DLC

• Must be located near

steering column

System Operation

• Closed Loop Mode

– PCM receives and processes information and adjusts outputs, resulting in new input data

• Open Loop Mode

– Used when the engine is cold

– PCM does not respond to feedback information – Makes decisions based on programming

OBD II Monitoring Capabilities

• Monitors to detect failing systems

• Illuminates the MIL before the failure

• Performs tests on subsystems

• Some monitors run continuously

• Other monitors only run under certain

operating conditions, called enable criteria

OBD II Trip

Catalyst Efficiency Monitor

• Uses two oxygen

• Most OBD II systems

allow about 2% rate

Type A Misfires

• Checked for at 200-rpm increments

• A misfire between 2% and 20% is excessive

• PCM may shut off fuel injector(s)

• If injector(s) not shut off, the MIL flashes

• If injector(s) are shut off, the MIL

illuminates

Fuel System Monitoring

• The PCM monitors and adjusts fuel delivery based on oxygen sensors feedback

• Short term fuel trim (STFT) makes minor

injector pulse-width adjustments

• Long term fuel trim (LTFT) is set by the

effectiveness of STFT

• The fuel trim monitor is continuous

Heated Oxygen Sensor Monitor

• Rich to lean and lean to rich response times

• Report time of sensors gives an indication of heater circuit operation

• All HO2S monitored once per drive cycle

• The monitor will vary fuel delivery to check

HO2S response

EGR System Monitoring

• Some systems monitor EGR temperature

• Other systems use the MAP sensor data

• Monitors EGR operation, flow rates, and opens and shorts in the circuit

Evaporative Emission System Monitor (EVAP)

• Tests the ability of the fuel tank to hold pressure

• Also tests the systems ability to purge fumes from the charcoal canister

Enhanced EVAP Systems

• In use since 2003

• Detects leaks and restrictions

• Checks EVAP system integrity

• Performs a vacuum test

• Uses a special fuel filler cap

• Loose or missing filler cap will set an EVAP code

Secondary Air Injection (AIR) System Monitor

• Can be tested by injecting air upstream of

HO2S sensor

• Many systems inject air into exhaust

manifold during open loop

• Air then injected into catalytic converter during closed loop

Comprehensive Component Monitor (CCM)

• Continuous monitor

• Looks at any electronic input that could affect emissions

• Monitors sensor range values

• Checks frequency input rationality

• Monitors outputs by checking voltage

• Must illuminate if an emissions fault is

detected

• MIL may stay on or blink

• MIL may go back off but a DTC and freeze frame are stored

• If the fault is not detected for 40 key cycles, the DTC and freeze frame are erased

OBD II Trouble Codes

• DTCs are standardized

Freeze Frame Data

• PCM takes a snapshot of activity when the MIL is illuminated

• Used by PCM for comparison of operating conditions if the same problem reoccurs

• Can be useful by technicians

• Erased if the DTC is erased

Test Modes

• All OBD II systems have same basic test

modes accessible with an OBD II scan tool

• Mode 1 – parameter ID (PID) mode

– Allows access to current data values, calculated values, and system status information

– Some PID values are manufacturer specific

Test Modes (cont’d)

• Mode 2 – freeze frame data access mode

• Mode 3 – access to stored DTCs

• Mode 4 – PCM reset mode

– Resets all DTCs, freeze frames, DTC histories, monitor test results, and monitor status

• Mode 5 – O2 sensor monitoring test

– Actual O2 sensor outputs during test cycle

– Used for catalyst efficiency monitoring

Test Modes (cont’d)

• Mode 6 – hexadecimal data

– Can be used for non-continuous system problem identification

• Mode 7 – test results for continuous monitoring systems

• Mode 8 – bidirectional control request

• Mode 9 – vehicle information request

Troubleshooting OBD II Systems

• Interview the customer

• Check the MIL

• Connect scan tool

• Check DTCs and freeze frames

• Check service history and information

• Record data and clear DTCs

• Visual inspection

Troubleshooting OBD II (cont’d)

• Check DTCs and monitors

Intermittent Faults

• May not set DTC or light the MIL

• Check history DTCs

• Evaluate symptoms and conditions

• Identify circuit or system that may be at fault

• Follow intermittent procedures in manual

• Visual inspection

• Test circuit wiring

Serial Data

• PIDs are codes used to request data from PCM

• Scan tools request and receive serial data

• Scan tool PID requests information from a device on the network

• Many PIDs are standard but not all are

supported by all manufacturers

Diagnosing OBD I Systems

• Limited self-diagnostic capability

• Hard faults (on-demand) occur at time of self-test

• Intermittent faults not present at self-test

can store a DTC for a number of key cycles

• Several different methods to access DTCs

• Perform a thorough visual inspection