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Lincoln Corsair: Evaporative Emissions - 2.0L EcoBoost (177kW/240PS) – MI4 / Description and Operation - Evaporative Emissions - System Operation and Component Description

Lincoln Corsair 2020-2022 Service Manual / Powertrain / Engine / Evaporative Emissions - 2.0L EcoBoost (177kW/240PS) – MI4 / Description and Operation - Evaporative Emissions - System Operation and Component Description

System Operation

System Diagram


Item Description
1 Air Cleaner (ACL) outlet pipe
2 EVAP ejector
3 Turbocharger to CAC tube
4 Check valve
5 EVAP purge valve
6 Check valve
7 Intake manifold
8 Fuel tank filler pipe
9 EVAP canister
10 Fuel vapor vent valve
11 Fuel Tank Pressure (FTP) sensor and tube
12 EVAP vapor blocking valve
13 Fuel tank
14 EVAP canister inlet filter
15 Fuel level sensor
16 EVAP canister vent solenoid

Evaporative Emission (EVAP) Systems

The EVAP system prevents fuel vapor build up in the sealed fuel tank. Fuel vapors trapped in the sealed tank are vented through the vapor valve assembly on top of the tank. The vapors leave the valve assembly through a single vapor line and continue to the EVAP canister for storage until the vapors are purged to the engine for burning.

All applications required to meet OBD regulations use the enhanced EVAP system.

Enhanced Evaporative Emission (EVAP) System

The enhanced EVAP system consists of a fuel tank, fuel filler cap or capless fuel tank filler pipe, fuel tank mounted or inline fuel vapor control valve, fuel vapor vent valve, EVAP canister, fuel tank mounted or fuel pump mounted or inline fuel tank pressure (FTP) sensor, EVAP purge valve, EVAP check valve (if equipped), intake manifold hose assembly, EVAP canister vent valve, PCM and connecting wires, and fuel vapor hoses. The enhanced EVAP system, including all the fuel vapor hoses, can be checked when a leak is detected by the PCM .

  • The enhanced EVAP system uses inputs from the CHT sensor or ECT sensor, the IAT sensor, the MAF sensor, the FTP sensor and vehicle speed to provide information about engine operating conditions to the PCM . The PCM uses the fuel level input (FLI) and FTP sensor signals to determine activation of the EVAP leak check monitor based on the presence of vapor generation or fuel sloshing.
  • The PCM determines the desired amount of purge vapor flow to the intake manifold for a given engine condition. The PCM then outputs the required signal to the EVAP purge valve. The PCM uses the enhanced EVAP system inputs to evacuate the system using the EVAP purge valve, seal the enhanced EVAP system from the atmosphere using the EVAP canister vent valve, and uses the FTP sensor to observe total vacuum lost for a period of time.
  • The EVAP canister vent valve seals the enhanced EVAP system to atmosphere during the EVAP leak check monitor.
  • The PCM outputs a duty cycle between 0% and 100% to control the EVAP purge valve.
  • The FTP sensor monitors the fuel tank pressure during engine operation and continuously transmits an input signal to the PCM . During the EVAP monitor testing, the FTP sensor monitors the fuel tank pressure or vacuum bleed up.
  • A valve inside the fuel tank mounted fuel vapor tube assembly prevents liquid fuel from entering the EVAP canister and the EVAP purge valve under any vehicle altitude, handling, or rollover condition.
  • On turbocharged engines, the EVAP check valve prevents boost pressure from entering the EVAP system.
  • On turbocharged engines, the turbocharger creates boost pressure in the intake manifold.
  • On turbocharged engines, an EVAP ejector is used to create a vacuum in the purge line during boost conditions. When in boost conditions a percentage of the boost pressure is applied to the EVAP ejector to create a vacuum. This vacuum draws purge vapors through the EVAP ejector into the intake air system upstream of the turbocharger.
  • The normally open VBV is a PCM controlled valve that blocks the flow of vapors from the fuel tank to the EVAP canister during engine operation. Closing the VBV during engine operation allows the EVAP system to purge the EVAP canister without purging the fuel tank. The VBV will open to relieve excess fuel tank pressure if the fuel tank pressure reaches a maximum calibrated value.

Engine On EVAP Leak Check Monitor

The engine on EVAP leak check monitor is executed by the individual components of the enhanced EVAP system as follows:

  • The EVAP purge valve controls the flow of vacuum from the engine and creates a target vacuum on the fuel tank.
  • The EVAP canister vent valve seals the EVAP system from the atmosphere. It is closed by the PCM (100% duty cycle) to allow the EVAP purge valve to achieve the target vacuum on the fuel tank.
  • The fuel tank pressure (FTP) sensor is used by the engine on EVAP leak check monitor to determine if the target vacuum necessary to carry out the leak check on the fuel tank is reached. Once the target vacuum on the fuel tank is achieved, the change in fuel tank vacuum over a calibrated period of time determines if a leak exists.
  • If the initial target vacuum cannot be reached, the DTC P0455 (gross leak detected) sets. The engine on EVAP leak check monitor aborts and does not continue with the leak check portion of the test. If the initial target vacuum cannot be reached after a refueling event and the purge vapor flow is excessive, the DTC P0457 (fuel cap off) sets.

If the initial target vacuum is exceeded, a system flow concern exists and the DTC P1450 (unable to bleed up fuel tank vacuum) is set. The engine on EVAP leak check monitor aborts and does not continue with the leak check portion of the test.

If the vacuum increase is quicker than expected, a blocked fuel vapor tube is suspected and if confirmed after an intrusive test, the DTC P144A sets.

If the target vacuum is achieved on the fuel tank, the change in the fuel tank vacuum (bleed up) is calculated for a calibrated period of time. The calculated change in fuel tank vacuum is compared to a calibrated threshold for a leak from an opening of 1.0 mm (0.040 inch) in the enhanced EVAP system. If the calculated bleed up is less than the calibrated threshold, the enhanced EVAP system passes. If the calibrated bleed up exceeds the calibrated threshold, the test aborts. The test can be repeated up to 3 times.

If the bleed up threshold is still being exceeded after 3 tests, a vapor generation test is carried out before the DTC P0442 (small leak detected) sets. This is accomplished by returning the enhanced EVAP system to atmospheric pressure by closing the EVAP purge valve and opening the EVAP canister vent valve. Once the FTP sensor observes the fuel tank is at atmospheric pressure, the EVAP canister vent valve closes and seals the enhanced EVAP system.

If the bleed up threshold is still being exceeded after 3 tests, a vapor generation test is carried out before DTC P0442 (small leak detected) sets. This is accomplished by returning the enhanced EVAP system to atmospheric pressure by closing the EVAP purge valve and opening the EVAP canister vent valve. Once the FTP sensor observes the fuel tank is at atmospheric pressure, the EVAP canister vent valve closes and seals the enhanced EVAP system.

The fuel tank pressure build up over a calibrated period of time is compared to a calibrated threshold for pressure build up due to vapor generation. If the fuel tank pressure build up exceeds the threshold, the leak test results are invalid due to vapor generation. The engine on EVAP leak check monitor attempts to repeat the test again.

If the fuel tank pressure build up does not exceed the threshold, the leak test results are valid and DTC P0442 sets.

  • If the 1.0 mm (0.040 inch) test passes, the test time is extended to allow the 0.5 mm (0.020 inch) test to run. The calculated change in fuel vacuum over the extended time is compared to a calibrated threshold for a leak from a 0.5 mm (0.020 inch) opening. If the calculated bleed up exceeds the calibrated threshold, the vapor generation test is run. If the vapor generation test passes (no vapor generation), an internal flag sets in the PCM to run a 0.5 mm (0.020 inch) test at idle (vehicle stopped). On the next start following a long engine OFF period, the enhanced EVAP system is sealed and evacuated for the first 10 minutes of operation. If the appropriate conditions are met, a 0.5 mm (0.020 inch) leak check is conducted at idle. If the test at idle fails, DTC P0456 sets. There is no vapor generation test with the idle test.
  • The MIL is activated for any enhanced EVAP system component DTCs.

Engine Off Natural Vacuum (EONV) EVAP Leak Check Monitor

The EONV EVAP leak check monitor is executed during ignition OFF, after the engine on EVAP leak check monitor is completed. The EONV EVAP leak check monitor determines a leak is present when the naturally occurring change in fuel tank pressure or vacuum does not exceed a calibrated limit during a calibrated amount of time. A separate, low power consuming, microprocessor in the PCM manages the EONV leak check. The engine OFF EVAP leak check monitor is executed by the individual components of the enhanced EVAP system as follows:

  • The EVAP purge valve is normally closed at ignition OFF.
  • The normally open EVAP canister vent valve remains open for a calibrated amount of time to allow the fuel tank pressure to stabilize with the atmosphere. During this time period the fuel tank pressure (FTP) sensor is monitored for an increase in pressure. If pressure remains below a calibrated limit the EVAP canister vent valve is closed by the PCM (100% duty cycle) and seals the EVAP system from the atmosphere.
  • The EONV EVAP leak check monitor uses the FTP sensor to determine if the target pressure or vacuum necessary to complete the EONV EVAP leak check monitor on the fuel tank is reached. If the target pressure or vacuum on the fuel tank is achieved within the calibrated amount of time, the test is complete.
  • The EONV EVAP leak check monitor uses the naturally occurring change in fuel tank pressure as a means to detect a leak in the EVAP system. At ignition OFF, a target pressure and vacuum is determined by the PCM . These target values are based on the fuel level and the ambient temperature at ignition OFF. As the fuel tank temperature increases, the pressure in the tank increases and as the temperature decreases a vacuum develops. If a leak is present in the EVAP system the fuel tank pressure or vacuum does not exceed the target value during the testing time period. The EONV EVAP leak check monitor begins at ignition OFF. After ignition OFF the normally open EVAP canister vent valve remains open for a calibrated amount of time to allow the fuel tank pressure to stabilize with the atmosphere. During this time period the FTP sensor is monitored for an increase in pressure. If pressure remains below a calibrated limit the EVAP canister vent valve is closed by the PCM (100% duty cycle) and seals the EVAP system from the atmosphere.

If the pressure on the fuel tank decreases after the EVAP system is sealed, the EONV EVAP leak check monitor begins to monitor the fuel tank pressure. When the target vacuum is exceeded within the calibrated amount of time the test completes and the fuel tank pressure and time since ignition OFF information is stored. If the target vacuum is not reached in the calibrated amount of time, a leak is suspected and the fuel tank pressure and time since ignition OFF information is stored.

If the pressure on the fuel tank increases after the EVAP system is sealed, but does not exceed the target pressure within a calibrated amount of time, the EVAP canister vent valve is opened to allow the fuel tank pressure to again stabilize with the atmosphere. After a calibrated amount of time the EVAP canister vent valve is closed by the PCM PCM and seals the EVAP system. When the fuel tank pressure exceeds either the target pressure or vacuum within the calibrated amount of time, the test completes and the fuel tank pressure and time since ignition OFF information is stored. If the target pressure or vacuum is not reached in the calibrated amount of time, a leak is suspected and the fuel tank pressure and time since ignition OFF information is stored.

On ISO 14229 vehicles, a fast initial response occurs during the first 4 tests after the battery is disconnected or the DTCs are cleared. The PCM processes unfiltered data to quickly indicate a fault is present. The MIL illuminates if the PCM suspects a leak within 2 consecutive trips after a DTC clear or a battery disconnect using the fast initial response logic.

A step change logic becomes active after the 4th EONV monitor test. The step change logic detects an abrupt change from a no leak condition to a suspected leak condition. The MIL illuminates if the PCM suspects a leak within 2 consecutive trips using the step change logic.

During the EONV monitor test the PCM uses an exponentially weighted moving average to filter test data. The PCM uses this average after the fourth EONV test and illuminates the MIL on the first trip when the exponentially weighted moving average is greater than a calibrated threshold. When a leak is suspected a DTC sets and the MIL is illuminated.

On non ISO 14229 vehicles, when a leak is suspected, the PCM uses the stored fuel tank pressure and time since ignition OFF information from an average run of 4 tests to suspect a leak. Some vehicles use an alternative method of a single run of 5 tests to determine the presence of a leak. If a leak is still suspected after 2 consecutive runs of 4 tests, (8 total tests) or one run of 5 tests, a DTC sets and the MIL is illuminated.

  • The EONV EVAP leak check monitor is controlled by a separate low power consuming microprocessor inside the PCM . The fuel level input, fuel tank pressure, and battery voltage are inputs to the microprocessor. The microprocessor outputs are the EVAP canister vent valve and the stored test information. If the separate microprocessor is unable to control the EVAP canister vent valve or communicate with other processors a DTC sets.
  • The MIL is activated for any enhanced EVAP system component DTCs.

Component Description

Evaporative Emission (EVAP) Canister Vent Valve

The EVAP canister vent valve (located in the EVAP canister dust box) is part of the enhanced EVAP system controlled by the PCM . During the EVAP leak check monitor, the EVAP canister vent valve seals the EVAP canister from the atmospheric pressure. This allows the EVAP purge valve to achieve the target vacuum in the fuel tank during the EVAP leak check monitor.

Evaporative Emission (EVAP) Check Valve

The EVAP check valve is used on turbocharged engines to prevent boost pressure from forcing open the EVAP purge valve and entering the EVAP system. The valve is open under normal engine vacuum. The valve closes during boost conditions to prevent the fuel tank from being pressurized and hydrocarbons forced out of the EVAP system into the atmosphere through the EVAP canister vent valve. When the engine is OFF, or at atmospheric pressure, the EVAP check valve is in an indeterminate state. The EVAP check valve is an integral part of the EVAP purge valve assembly.

Evaporative Emission (EVAP) Ejector

The EVAP ejector is used on turbocharged engines to create a vacuum in the EVAP purge line from the EVAP purge valve to the intake air system. During boost conditions, boost pressure flows through a venturi inside the EVAP ejector creating a vacuum in the EVAP purge line to the intake air inlet to the turbocharger. When the second EVAP check valve is open, the purge vapor is drawn through the EVAP ejector into the intake air tube, through the turbocharger and charge air cooler, to the intake manifold.

Evaporative Emission (EVAP) Purge Valve

The EVAP purge valve (located near the engine) is part of the enhanced EVAP system controlled by the PCM . This valve controls the flow of vapors (purging) from the EVAP canister to the intake manifold during various engine operating modes. The EVAP purge valve is a normally closed valve. The PCM outputs a duty cycle between 0% and 100% to control the EVAP purge valve.

Evaporative Emission (EVAP) Vapor Blocking Valve

The EVAP vapor blocking valve is a normally open valve, electrically closed by the PCM , to isolate the fuel tank from the rest of the EVAP system. The EVAP vapor blocking valve will automatically open to relieve excess pressure or vacuum, in the fuel tank, if the pressure or vacuum reaches a maximum calibrated value.

Fuel Tank Pressure (FTP) Sensor

The in tank FTP sensor or the inline FTP sensor measures the fuel tank pressure.

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