Tue Jun 14 16:01:13 CEST 2016
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falloutboy
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In einem Thread über Chevrolet Caprice kam die Frage nach dem EVAP System, seine Funktion und Diagnose auf. Hier einmal mehr über das System, zuerst der allgemeine Wikipedia Eintrag dazu:
Hier zB die System Beschreibung für ein "moderneres" Fahrzeug
Document ID# 304317 - 1999 Chevrolet/Geo Alero Export Evaporative Emission (EVAP) Control System Operation Description
Purpose
The basic Evaporative Emission (EVAP) Control system used on all vehicles is the charcoal canister storage method. This method transfers fuel vapor from the fuel tank to an activated carbon (charcoal) storage device (canister) to hold the vapors when the vehicle is not operating. When the engine is running, the fuel vapor is purged from the carbon element by intake air flow and consumed in the normal combustion process.
Enhanced EVAP System Operation
FIGURE EVAP Control System Overview(c) (1) EVAP Vent Valve/Solenoid (2) EVAP Vent Valve/Solenoid Ignition Feed Circuit Terminal (3) EVAP Vent Valve/Solenoid Control Circuit Terminal (4) EVAP Vent Valve/Solenoid Filter (5) EVAP Vapor Lines (6) Fuel Tank Pressure Sensor (7) Fuel Tank Pressure Sensor Ground Circuit Terminal (8) Fuel Tank Pressure Sensor Signal Circuit Terminal (9) Fuel Tank Pressure Sensor Circuit 5 Volt Reference Circuit Terminal (10) Fuel Filler Pipe (11) Check Valve (Spitback) (12) Modular Fuel Sender Assembly (13) Fuel Limiter Vent Valve (FLVV) (14) Pressure/Vacuum Relief Valve (Optional) (15) EVAP Canister (16) EVAP Canister Purge Valve/Solenoid Ignition Feed Circuit Terminal (17) EVAP Canister Purge Valve/Solenoid Control Circuit Terminal (18) Intake Manifold Vacuum Source (19) EVAP Canister Purge Valve/Solenoid (20) EVAP Service Port The EVAP purge solenoid valve allows manifold vacuum to purge the canister. The Powertrain Control Module (PCM) supplies a ground to energize the EVAP purge solenoid valve (purge on). The EVAP purge solenoid control is Pulse Width Modulated (PWM) or turned on and off several times a second. The PCM controlled PWM output is commanded when the appropriate conditions have been met:
Canister purge PWM duty cycle varies according to operating conditions determined by mass air flow, fuel trim, and intake air temperature. Canister purge will be disabled if TP angle increases to above 70%. Canister purge will be re-enabled when TP angle decreases below 66%.
The evaporative leak detection diagnostic strategy is based on applying vacuum to the EVAP system and monitoring vacuum decay.
The fuel level sensor input to the PCM is used to determine if the fuel level in the tank is correct to run the EVAP diagnostic tests. To ensure sufficient volume in the tank to begin the various diagnostic tests, the fuel level must be between 15% and 85%.
The PCM monitors system vacuum level via the fuel tank pressure sensor input.
OBD II Evaporative Emission System - Fuel Tank Vacuum Sensing General Description (Enhanced EVAP) The evaporative system includes the following components:
Results of Incorrect Operation
EVAP Purge Solenoid, EVAP Vent Solenoid and Fuel Tank Pressure Sensor The evaporative leak detection diagnostic strategy is based on applying vacuum to the EVAP system and monitoring vacuum decay.
Before the EVAP system diagnostic tests are run the following conditions must be present:
The EVAP system diagnostic tests will be run following a cold start, as indicated by the ECT and IAT sensors. The fuel level sensor input to the PCM is used to determine if the fuel level in the tank is correct to run the EVAP diagnostic tests. To ensure sufficient volume in the tank to begin the various diagnostic tests, the fuel level must be between 15% and 85%.
The PCM monitors vacuum level via the fuel tank pressure sensor input. At an appropriate time, the EVAP purge solenoid and the EVAP vent solenoid are turned on, allowing engine vacuum to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP purge solenoid is turned off, sealing the system. A leak is detected by monitoring for a decrease in vacuum level over a given time period, all other variables remaining constant. A small leak in the system will cause DTC P0442 to be set.
If the desired vacuum level cannot be achieved in the test described above, a large leak or a faulty EVAP purge solenoid is indicated. This can be caused by the following conditions:
Any of the above conditions can set DTC P0440.
A restricted or blocked EVAP canister vent path is detected by drawing vacuum into the EVAP system, turning off the EVAP vent solenoid and the EVAP purge solenoid (EVAP vent solenoid Open, EVAP purge PWM 0%) and monitoring the fuel tank pressure sensor input. With the EVAP vent solenoid open, any vacuum in the system should decrease quickly unless the vent path is blocked. A blockage can be caused by the following conditions:
If any of these conditions are present, DTC P0446 will set.
The system checks for conditions that cause the EVAP system to purge continuously by commanding the EVAP vent solenoid on and the EVAP purge solenoid off (EVAP vent solenoid CLOSED, EVAP purge PWM 0%). If fuel tank pressure level increases during the test, a continuous purge flow condition is indicated. This can be caused by the following conditions:
If any of these conditions are present, DTC P1441 will set.
Refer to the DTC charts for further diagnostic procedures regarding the EVAP system.
Visual Check of Evaporative Emission Canister Cracked or damaged, replace canister. Fuel leaking from the canister, replace canister and check lines and line routing.
Hier nur die Beschreibung des älteren Systems, anhand eines 1980 Chevrolet Caprice
Fig. 1: The evaporative emission canister is usually mounted in the side of the engine compartment
Fig. 2: Evaporative emission control system schematic for early model "open" design canisters
Fig. 3: Common evaporative emission control schematic for Chevrolet 5.0L engines equipped with thermal vacuum control
Fig. 4: Common closed canister evaporative control schematic for carbureted vehicles equipped with a vacuum solenoid
Fig. 5: Evaporative emission control schematic — fuel injected vehicles
All gasoline vehicles covered by this manual are equipped with an evaporative emission control system which is designed to reduce the amount gasoline vapors which escape into the atmosphere. Float bowl emissions are controlled by internal carburetor modifications and, on later model vehicles, by a vapor line to the canister. Redesigned bowl vents, reduced bowl capacity, heat shields and improved intake manifold-to-carburetor (or throttle body on fuel injected vehicles) insulation reduce vapor loss. The venting of fuel tank vapors into the air has been stopped by means of the carbon canister storage method. This method transfers fuel vapors to an activated carbon storage device which absorbs and stores the vapor that is emitted from the engine's induction system while the engine is not running. When the engine is running, the stored vapor is purged from the carbon storage device by the intake air flow and then consumed in the normal combustion process. The system, in its simplest form, works when manifold vacuum reaches a certain point and opens a purge control valve mounted atop or near the charcoal storage canister. This allows air to be drawn into the canister, thus forcing the existing fuel vapors back into the engine to be burned normally.
The purge function on most earlier model vehicles was controlled by a Thermal Vacuum Switch (TVS) located inline between the canister and the carburetor/intake manifold. The thermal vacuum switch was threaded into a coolant passage such as the thermostat housing and would be activated by engine coolant temperature. As the engine warmed, the switch would open to allow vacuum to the canister or canister control valve.
Later vehicles switched from thermal to electronic control. The purge control on the 231 and on all fuel injected engines is electronically controlled by a normally opened inline purge solenoid which is itself activated by the Electronic Control Module (ECM). On the 231 and most fuel injection systems through 1987, when the system is in the Open Loop mode, the solenoid valve is energized, blocking all vacuum to the purge valve. When the system is in the Closed Loop mode, the solenoid is de-energized, thus allowing existing vacuum to operate the purge valve. This releases the trapped fuel vapor and it is forced into the induction system.
For almost all 1988–89 fuel injected vehicles, a new purge control solenoid was used. This solenoid was a Normally Closed (N/C) component which worked on opposite signals to its predecessor. On these vehicles the ECM would de-energize the solenoid during cold engine operation or idle conditions. When de-energized the solenoid would block all vacuum preventing canister purge. Once the engine was fully warmed and operated above idle, the ECM would energize the solenoid, allowing vacuum to purge the canister of stored fuel vapors.
Many of the carbureted vehicles covered by this book are equipped with a float bowl vent to the canister. On these vehicles a vacuum valve is used to prevent vapor purge from the float bowl when the engine is running. Whenever the engine is off, the valve allows vapors to travel from the float bowl to the canister.
Though a few of the earlier vehicles covered here were equipped with carbon canisters of the "Open" design, meaning that air is drawn in through the bottom (filter) of the canister, most are equipped with a "Closed" design canister which uses a sealed bottom. On later model vehicles equipped with "Closed" design canisters, incoming air which is drawn directly from the air cleaner.
SERVICE
Besides a periodic visual inspection of the system's components, the only periodic service necessary (on early model vehicles so equipped) is canister filter replacement. Later vehicles are equipped with a sealed canister that is not equipped with a replaceable cartridge. On these vehicles, the entire canister assembly must be replaced if any damage occurs or any problems are found with the canister itself.
NOTE: Remember that the fuel tank filler cap is an integral part of the system in that it is designed to seal in fuel vapors. If it is lost or damaged, make sure the replacement is of the correct size and fit so a proper seal can be obtained.
Periodically check for cracks or leaks in the vacuum lines or in the canister itself. The lines and fittings can usually be reached without removing the canister. Cracks or leaks in the system may cause poor idle, stalling, poor driveability, fuel loss or a fuel vapor odor.
Vapor odor and fuel loss may also be caused by; fuel leaking from the lines, tank or injectors, loose, disconnected or kinked lines or an improperly seated air cleaner and gasket.
If the system passes the visual inspection and a problem is still suspected, check the basic operation of the components:
The line from the fuel tank to the canister must be clear and unobstructed. When the engine is OFF, air should pass from the fuel tank towards the canister freely in order to allow vapors to collect in the canister. Make sure the line is free of kinks or obstructions. While the engine is not running, air should NOT be allowed out of the canister. If equipped with a float bowl vent, the vacuum valve should only allow air to be blown from the carburetor float bowl towards the canister when no vacuum is applied (engine is not running). To test this valve, attempt to blow air through the valve towards the canister with the engine OFF, there should be little or no restriction. Use a hand vacuum pump to apply approximately 15 in. Hg (51 kPa) to the valve, now air should no longer flow towards the canister. Thermal valves are usually designed to open, allowing vacuum or air pressure towards the canister or control valve only when the engine is warm. Attach a length of hose to the engine side fitting and try blowing towards the canister. Air should be felt at the canister side fitting, only when the engine is at normal operating temperature. NOTE: When testing valves by blowing air through them, be careful that you are blowing in the proper direction of flow. Many valves are designed to only allow air to flow in one direction and a proper working valve may seem defective if it is tested with air flow only in the wrong direction.
Normally open solenoid valves, which are used on some engines before 1988, should close when energized and open when de-energized. Try blowing air through the valve fittings when the engine is OFF, it should flow with little or no resistance. When the engine is running the solenoid should energize during engine warm-up and de-energize once it has reached normal operating temperature. Normally closed solenoid valves, used on most 1988–89 engines, should open when energized and close when deenergized. Try blowing air through the valve fittings when the engine is OFF, air should not flow. When the engine is running the solenoid should de-energize during engine warm-up and energize once it has reached normal operating temperature. Most vacuum and control valves, with the exception of the float bowl valve, are designed to open when vacuum is applied. In either case, all are designed to allow air to pass through only during one condition (vacuum on or off depending on design). To test vacuum valves, try to blow air through the valve with and without vacuum applied. If air can pass through during only 1 of these conditions the valve is likely operating properly. On the other hand if air can always or never flow, the valve is defective. Use a hand vacuum pump to apply approximately 15 in. Hg (51 kPa) to the valve. The valve should open or close (as applicable) and hold the vacuum for at least 20 seconds, or the diaphragm is leaking and the valve must be replaced.
Und nochmal etwas offizieller für einen Document ID# 39915 - 1996 Chevrolet/Geo Caprice Evaporative Emission (EVAP) Control System
The Evaporative Emission (EVAP) control system used on all vehicles is the charcoal canister storage method. This method transfers fuel vapor from the fuel tank to an activated carbon (charcoal) storage device (canister) to hold the vapors when the vehicle is not operating. When the engine is running, the fuel vapor is purged from the carbon element by intake air flow and consumed in the normal combustion process.
Fuel Vapor Canister (1) Tank Tube (2) Air Tube (Fresh Air Inlet) (3) Purge Tube The Evaporative Emission (EVAP) control system uses a 1500 cc charcoal canister to absorb fuel vapors from the gas tank.
When gasoline vapor builds enough to overcome the spring tension of the EVAP pressure control valve, the vapor will flow to the canister where it is absorbed and stored by the charcoal. Under certain operating conditions the PCM will command the purge solenoid valve to open. This allows the vapor to flow into the intake manifold for combustion.
This system has a remote mounted canister purge control solenoid valve. The PCM operates this solenoid valve to control vacuum to the canister. Under cold engine or idle conditions, the solenoid valve is closed, which prevents vacuum from being applied to the canister. The PCM activates (or opens) the solenoid valve and allows purge under the following conditions:
EVAP Pressure Control Valve (1) Control Tube (2) Tube to Canister (3) Umbrella Valve (4) Restriction (5) Tube to Fuel Tank (6) Diaphragm (7) Diaphragm Spring
Evaporative Emission (EVAP) Pressure Control Valve This system uses an in-line EVAP pressure control valve as a pressure relief valve. When vapor pressure in the tank exceeds approximately 5 kPa (.7 psi) the diaphragm valve opens, allowing vapors to vent to the canister. A 1.14 mm (0.045 inch) orifice in the passage leading to the canister tube causes pressure to drop slowly, preventing the valve from oscillating (buzzing). When the tank pressure drops below 5 kPa (.7 psi), the valve closes causing vapors to be held in the fuel tank. Results of Incorrect Operation
If the solenoid valve is open, or is not receiving power, the canister can purge to the intake manifold at the incorrect time. This can allow extra fuel during warm-up, which can cause rough or unstable idle.
EVAP Vacuum Switch EVAP Purge Vacuum Switch The EVAP Purge Vacuum Switch is used by the PCM to monitor EVAP canister purge solenoid operation and purge system integrity. The EVAP Purge Vacuum Switch should be closed to ground with no vacuum present (0% EVAP Purge PWM). With EVAP Purge PWM at 25% or greater, the EVAP Purge Vacuum Switch should open.
An incorrect EVAP Purge system flow should set a DTC P0441. A continuous purge condition with no purge commanded by the PCM should set a DTC P1441. Refer to Evaporative Emission (EVAP) Control System for a complete description of the EVAP system.
The Evaporative Emission (EVAP) canister purge solenoid valve and the EVAP Vacuum switch diagnosis is covered in the following DTCs:
EVAP Control System Schematic (1) Throttle Body (2) EVAP Solenoid Valve (3) EVAP Vacuum Switch (4) EVAP Canister (5) EVAP Pressure Control Valve (6) Floating Roll-Over Valve (7) Fuel Tank Visual Check of EVAP Canister If cracked or damaged, replace EVAP canister.
Evaporative Emission (EVAP) Pressure Control Valve
With a hand vacuum pump, apply approximately 51 kPa (15 in. Hg) to the control vacuum tube. After ten seconds, there should be at least 17 kPa (5 in. Hg) vacuum remaining. Be sure the hand vacuum pump being used does not have an internal leak and the hose connections to control vacuum tube and pump are secure. If after 10 seconds there is less than 17 kPa (5 in. Hg) vacuum, the valve must be replaced.
With 51 kPa (15 in. Hg) vacuum still applied to the control vacuum tube, attach a short piece of hose to the valves tank tube side. Blow into the tube. You should feel the air pass through the valve. If air does not pass through, the valve must be replaced. |
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Tue Jun 14 16:12:14 CEST 2016 |
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