toyota training course t874 engine control systems II ch07

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toyota training course t874 engine control systems II ch07

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Section Fuel Systems Slide 79 T852f234 Fuel Systems The purpose of the fuel injection system is to precisely inject a metered amount of fuel at the correct time Based on input sensor signals and internal programming, the ECM decides when to turn each injector ON and OFF Port fuel injection introduces fuel into the intake manifold, where it mixes with intake air The air/fuel mixture then is drawn into the combustion chamber through the intake valve Because the timing of air/fuel entry into the combustion chamber is controlled by the engine’s valve system, the timing of fuel injection is less important than the volume of fuel injected Typical Port Injection Most port fuel injection systems have the following components: Components • Fuel tank and lines store fuel and route it where needed • Fuel filter removes impurities from fuel • Feed fuel pump draws fuel from the tank (under control of Fuel Pump ECU in certain port injection systems) • Pressure regulator controls pressure within the system • Pulsation damper reduces pressure fluctuations within the system • Port fuel injectors open and close on command from the ECM; when an injector opens, system pressure causes fuel to flow through the injector Toyota Engine Control Systems I Course 852 69 Fuel Delivery — Return Type Fuel Systems Slide 80 T852f181 Return Type Fuel Delivery In a return type fuel delivery system, fuel that is not needed for engine operation is returned to the tank through a fuel return line Some port injection systems use return type delivery In a return type port injection system: • When the fuel pump runs, pressurized fuel flows out of the tank, through the fuel filter to the fuel rail and the pressure regulator • The pressure regulator maintains fuel pressure in the rail at a specified value This value will vary in relation to either manifold vacuum or atmospheric pressure, depending on model • Excess fuel not needed for engine operation is returned to the tank through a fuel return line Return type systems have two major disadvantages: • The return fuel delivery system adds weight and creates more opportunity for leakage • Fuel returning to the tank has been heated by the engine, which could result in increased evaporative emissions 70 TOYOTA Technical Training Fuel Delivery — Returnless Type Fuel Systems Slide 81 208EG117 Returnless Type Fuel Delivery In a returnless type fuel delivery system, there is no return of fuel to the tank This eliminates the weight and complication of return lines and the return of heated fuel to the tank Many current port injection systems use returnless type fuel delivery The location and operation of the pressure regulator is the main functional difference between return and returnless designs In a returnless system: • When the fuel pump runs, pressurized fuel flows from the pump to the in-tank pressure regulator This spring-loaded regulator maintains a set pressure value in the system (does not vary regardless of manifold vacuum or atmospheric pressure) • At the pressure regulator, excess fuel is directed to the bottom of the fuel tank while pressurized fuel is sent out of the fuel tank, through the fuel filter, pulsation damper, and into the fuel rail • Fuel pressure in this system is maintained at a constant and higher pressure than in the return type fuel system ECM programming and a higher system pressure eliminate the need for a modulated pressure regulator Toyota Engine Control Systems I Course 852 71 Fuel Pump: In-tank Electric Fuel Systems Slide 82 T852f183, T852f185 Fuel Pump The in-tank fuel pump on all models draws fuel from the storage tank and delivers it to the injection system The fuel pump’s pumping capacity is designed to exceed engine requirements This ensures that there will always be enough fuel to meet engine demands In-Tank Electric An electric fuel pump is mounted in the tank and immersed in fuel The fuel cools and lubricates the pump When the pump is turned ON, it draws fuel in through a filtered inlet and discharges pressurized fuel through the outlet port An outlet check valve in the discharge outlet maintains a residual pressure in the system when the engine is OFF This has two benefits: • Improved starting characteristics — without residual fuel pressure, the system would have to be pressurized each time the engine was started This would increase engine starting (cranking) time • Reduced chance of vapor lock — when a hot engine is shut off, fuel temperature in the lines around the engine increases Keeping the system pressurized raises the boiling point of the fuel and helps prevent the fuel from vaporizing A pressure relief valve will open if the fuel system becomes restricted This safety device prevents excess pressure from rupturing fuel lines or damaging the pump 72 TOYOTA Technical Training Fuel Pump: Jet Pump Fuel Systems Slide 83 036EG70TE , 036EG39TE Jet Pump Some models use a jet pump in addition to the standard in-tank electric pump This saddle tank design accommodates the propeller shaft A saddle tank tends to cause fuel to be present in both chamber A and chamber B when the fuel level is low To prevent this from occurring, the jet pump transfers the fuel from chamber B to chamber A The pressure difference created by the fuel as it passes through the venturi is used to draw the fuel out of chamber B and send it to chamber A Toyota Engine Control Systems I Course 852 73 Fuel Pump Controls: ECM ON/OFF Fuel Systems Slide 84 G43045 Fuel Pump Controls The most accurate way to determine the type of fuel control circuit is to look it up in the appropriate Repair Manual or EWD Basic methods include: • ON/OFF control by the ECM • Multiple speed control with Fuel Pump ECU: Larger displacement engines require a higher volume of fuel during starting and heavy load conditions A high capacity fuel pump can meet the demand but may also produce excessive noise and consume more power Multiple speed fuel pump control can help overcome the disadvantages and increase pump life The following descriptions are typical; not all systems will have exactly the components shown ON/OFF Control by the ECM The ECM controls the fuel pump based on engine operating conditions: • Engine start: During cranking, current from the ignition switch to the starter relay (ST) coil turns the relay ON Current also flows from the ignition switch to the STA terminal of the ECM When the STA signal and the crankshaft position signal (NE) are input to the ECM, Tr is turned ON, current travels through the coil of the circuit opening relay (C/OPN), the relay switches ON, power is supplied to the fuel pump and the pump operates • Engine running: Once the engine is running, the ECM continues to receive the NE signal and keeps the fuel pump ON • Engine stopped: When the engine stops, the NE signal stops and the ECM turns Tr OFF, allowing the C/OPN relay to open, causing the fuel pump to lose power and stop running as well 74 TOYOTA Technical Training Fuel Systems Fuel Pump Controls: 2-Speed with Resistor Slide 85 2-Speed Control with Resistor Low Speed Operation High Speed Operation ON-OFF and speed control of the fuel pump is controlled with a resistor based on signals from the ECM When the engine is idling and under normal driving conditions (when a small amount of fuel is required), the ECM turns ON the fuel pump control relay The relay switches to contact B, sending current through the resistor This reduces the available current and voltage to the fuel pump, causing it to run at low speed When the engine is operating at high speeds or under heavy load, the ECM turns OFF the fuel pump control relay The relay switches to contact A and the current to the fuel pump flows directly to the pump, bypassing the resistor This causes the fuel pump to run at high speed The fuel pump also runs at high speed while the engine is starting Toyota Engine Control Systems I Course 852 75 Fuel Pump Controls: 3-Speed Control with Fuel Pump ECU Fuel Systems Slide 86 T852f139/T852f194 3-Speed Control with Fuel Pump ECU In this system, the Fuel Pump ECU varies supply voltage to create three fuel pump speeds (high, medium, and low): • High speed: During starting and heavy load conditions, the ECM sends a HI signal (about volts) to the Fuel Pump ECU The ECU then supplies full battery power to the fuel pump • Medium speed: Under heavy loads at low speed, the ECM sends a pulsewidth modulated 2.5 volt signal to the Fuel Pump ECU The ECU then applies about 10 volts to the fuel pump to operate it at medium speed • Low speed: When idling or under light loads, the ECM sends a pulsewidth modulated 1.3 volt signal to the Fuel Pump ECU The ECU then applies 8.5 volts to the fuel pump, lowering operating noise and reducing power consumption • OFF: When the engine is stopped or stalls and when SRS deployment occurs, the ECM sends volts to the Fuel Pump ECU to stop the fuel pump 76 TOYOTA Technical Training Fuel Pump Interruption Fuel Systems Slide 87 T852f196/T852f197 Fuel Pump The fuel pump is shut off in certain types of collisions There are two Interruption methods for shutting off the fuel pump: ECM controlled and mechanical inertia switch ECM Controlled Inertia Switch Most late model vehicles shut off the fuel pump when any of the SRS airbags deploy When the ECM receives a deployment signal from the Airbag Sensor Assembly, the ECM turns OFF the Circuit Opening Relay Cycle the ignition switch to cancel fuel pump shutoff and restart the engine An inertia switch is found on Land Cruiser from 1998 to 2002 model years It includes a switch to shut OFF the fuel pump when the vehicle is involved in a collision to minimize fuel leakage Electrically, the fuel pump inertia switch is located between the ECM and Fuel Pump ECU The inertia switch consists of a ball, spring loaded link, contact point, and reset switch If the force of a collision is greater than a predetermined value, the ball will move and the spring loaded link will drop, opening the contact point This opens the circuit between the ECM and Fuel Pump ECU, and the fuel pump turns OFF If the fuel pump inertia switch has tripped, reset it by pushing up on the reset switch for at least one second Toyota Engine Control Systems I Course 852 77 Vacuum Pressure Regulator Fuel Systems Slide Slide88 T874f509, T874f310, T852f201/T852f202 T874f508 Fuel Pressure Fuel pressure must be regulated to ensure proper operation of the fuel Regulators injection system Although there are different types, all fuel pressure regulators maintain fuel pressure within a specified range so that it does not go too high or too low Vacuum Modulated Pressure Regulator The vacuum modulated pressure regulator maintains a constant pressure differential across the fuel injectors This means that fuel rail pressure will always be at a constant value above manifold absolute pressure Low intake manifold pressure (for example, at idle) pulls on the diaphragm, decreasing spring pressure This allows more fuel to return to the fuel tank, decreasing pressure in the fuel rail Opening the throttle increases manifold pressure With less vacuum on the diaphragm spring, pressure will increase, restricting fuel flow to the fuel tank This increases pressure in the fuel rail 78 TOYOTA Technical Training Fuel Delivery Lines and Connectors Fuel Systems Slide 92 T852f206/T852f207/T852f208/T852f209/T852f210/285EG38 Fuel Delivery A variety of materials and connectors are used within the fuel system Components Steel and synthetic materials are used, depending on component location and vehicle model It is critical that the correct procedures be followed when servicing the fuel lines and related components Inspect all tabs for damage, and replace any found Lines and Connectors Fuel Tank 82 Port injection system connectors may be the threaded type or the quick connector type The fuel tank is designed to safely contain the fuel and evaporative emissions Typically, it houses the fuel pump assembly and rollover protection valves (if applicable) TOYOTA Technical Training Fuel Filters Fuel Systems Slide 93 T852f211/T852f212 Fuel Filters Typically, there are two fuel filters in the fuel delivery system: • The first filter is located on the suction side of the fuel pump This filter prevents debris from damaging the fuel pump • The second filter is located between the pump and fuel rail to remove dirt and contaminants from the fuel before it is delivered to the injectors The injectors require extremely clean fuel, so this filter removes extremely small particles from the fuel The second filter may be part of the in-tank fuel pump assembly or outside the tank in the fuel line leading to the fuel rail Filters are designed to be maintenance-free with no required service replacement However, a restricted fuel filter may prevent the proper fuel pressure from reaching the injectors A restricted fuel filter may cause hard start, surge, low power under load, etc A completely clogged filter can prevent the engine from starting Toyota Engine Control Systems I Course 852 83 Pulsation Damper Fuel Systems Slide 94 T852f213/T852f214 Pulsation Damper Fluctuating fuel pressure can cause more or less than the desired amount of fuel to be injected Pulsation dampers help absorb changes in fuel pressure caused by the rapid opening and closing of the fuel injectors Different fuel system designs feature different damper designs: • Port injection system: If used, the pulsation damper is mounted on the fuel rail When pressure begins to increase, the spring loaded diaphragm retracts slightly, increasing fuel rail volume This momentarily prevents fuel pressure from becoming too high When pressure begins to drop, the spring loaded diaphragm extends, slightly reducing effective fuel rail volume This momentarily prevents fuel pressure from becoming too low The screw mounted at the top of the damper provides an easy check for fuel system pressure When the screw is up, the fuel rail is pressurized Under most conditions, this check is not adequate The screw is not adjustable (it is used to calibrate the damper at the factory) • Inner pipe pulsation damper: Some late model fuel injection systems use an inner pipe style pulsation damper This eliminates the use of a separate pulsation damper, making the fuel system more compact and lightweight This damper consists of a hollow inner pipe inside the fuel delivery pipe When fuel pressure fluctuates, the shape of the inner pipe changes with the pulsation, thus changing the internal capacity of the delivery pipe This change in capacity absorbs the fuel pulsations 84 TOYOTA Technical Training Port Fuel Injection Operation Fuel Systems Slide Slide96 T874f509, T852f217/T852f218/T852f818 T874f310, T874f508 Port Fuel Injection The fuel injector, when turned ON by the ECM, atomizes and directs fuel Operation into the intake manifold There is one injector per cylinder mounted in the intake manifold before the intake valve(s) Fuel Injectors Injectors are installed with an insulator/seal on the manifold end to insulate them from heat and prevent atmospheric pressure from leaking into the manifold The fuel delivery pipe secures the injector An O-ring between the delivery pipe and injector prevents fuel from leaking When replacing an injector it is critical that the correct injector be used Different engines require different injectors Injectors are designed to flow a specified amount of fuel when open In addition, the number of holes at the tip of the injector varies with engine and model year Inside the injector is a solenoid and needle valve The fuel injector circuit is usually a ground switched circuit To turn ON the injector, the ECM completes a path to ground The magnetic field pulls the needle valve up against spring pressure and fuel flows out of the injector When the ECM turns OFF the circuit, spring pressure forces the needle valve onto its seat and shuts off fuel flow NOTE: Confirm part numbers and resistance values before installing new fuel injectors Fuel injectors for one model may fit on another model, but could have different resistance values Installing an injector with the wrong resistance value may cause a no-start condition, driveability concerns, or ECM failure Toyota Engine Control Systems I Course 852 85 Fuel Cut Fuel Systems Slide Slide97 T874f509, T874f310, T852f229 T874f508 Fuel Cut The ECM controls fuel delivery differently according to engine and vehicle operating conditions: • Deceleration fuel cut: During closed throttle deceleration at moderate to high engine speeds, fuel delivery is not necessary or desirable To prevent excessive deceleration emissions and improve fuel economy, the ECM will not open the injectors under certain deceleration conditions The ECM will resume fuel injection at a calculated RPM Referring to the graph, fuel cutoff and resumption speeds are variable, depending on coolant temperature, A/C compressor clutch status, and the STP signal Essentially, when extra engine loads are present, the ECM will begin fuel injection earlier • Fuel Tau cut: A mode employed on some engines during long deceleration times with the throttle valve closed During these times, excess air, without the presence of fuel, cools the catalytic converter, reducing its efficiency To prevent this, the ECM very briefly pulses the injectors • Engine over-rev fuel cutoff: To prevent engine damage, a revlimiter is programmed into the ECM Any time the engine RPM exceeds the pre-programmed threshold, the ECM shuts off the injectors Once RPM falls below the threshold, the injectors are turned back ON Typically, the threshold RPM is slightly above the engine’s redline RPM 86 TOYOTA Technical Training • Vehicle over-speed fuel cutoff: On some vehicles, fuel injection is halted if the vehicle speed exceeds a predetermined threshold programmed into the ECM Fuel injection resumes after the speed drops below this threshold Open and Closed Loop Operation Fuel Systems Slide T874f509, T874f310,Slide T874f508 98 Open and Closed An open loop system does not monitor its output nor make adjustments Loop Operation based on its output An example of an open loop system is vehicle climate control (without automatic air conditioning) A system that controls its output by monitoring its output is called a closed loop system For example, the vehicle’s cruise control system adjusts vehicle speed by monitoring vehicle speed If speed is too low, the system responds by increasing vehicle speed When the ECM corrects the air/fuel ratio based on O2 or A/F sensors, the system is said to be in closed loop Other examples of closed loop systems include: • Voltage regulation • Ignition system knock control • Closed loop air/fuel ratio correction control Toyota Engine Control Systems I Course 852 87 Open Loop Mode Fuel Systems Slide Slide99 T874f509, T874f310, T852f234 T874f508 Open Loop Mode The ECM will be in open loop mode during: • Engine start • Low O2 or A/F sensor operating temperature • Fuel cutoff • Wide open throttle (WOT) If the engine will not go into closed loop mode, the problem may be no response from O2 or A/F sensors or a malfunction in the heater circuit Usually, no response from O2 or A/F sensors will set a DTC If there is a driveability problem that only occurs in closed loop, a fault in O2 or A/F sensor circuits or anything that disrupts the air/fuel ratio may be the cause 88 TOYOTA Technical Training Fuel Systems Closed Loop Mode Slide Slide 100 T874f509, T874f310, T852f235 T874f508 Closed Loop Mode (O2 Sensor) When in closed loop, the ECM uses the O2 sensor voltage signal to make minor corrections to the injection duration This is done to help the catalytic converter operate at peak efficiency When the voltage is higher than 450 mV, the air/fuel ratio is judged to be richer than the ideal air/fuel ratio, and the amount of fuel injected is reduced at a constant rate The reduction in the duration continues until the O2 sensor signal switches to a low voltage (lean air/fuel ratio) When the voltage signal is lower than 450 mV, the air/fuel ratio is judged to be leaner than the ideal air/fuel ratio so the amount of fuel injected is increased at a constant rate The increase in duration continues until the O2 sensor switches to high voltage (rich air/fuel ratio) At this point, the ECM will slowly decrease the amount of fuel injected, therefore the air/fuel ratio oscillates slightly richer or leaner than the ideal air/fuel ratio The result is an average air/fuel ratio of approximately 14.7:1 This produces the proper mixture of exhaust gases so that the catalytic converter operates at its most efficient level O2 sensor signal voltage abruptly changes at the ideal air/fuel ratio, and changes very little as the air/fuel ratio extends beyond ideal Because the ECM changes injection duration in gradual steps until the O2 sensor signal abruptly switches, fuel control is less precise than with an A/F sensor Toyota Engine Control Systems I Course 852 89 Closed Loop Mode, cont Closed Loop Mode (A/F Sensor) Fuel Systems With an A/F sensor, air/fuel mixture correction is faster and more precise The A/F sensor outputs a voltage signal that is relatively proportional to the air/fuel ratio The ECM then knows how much the air/fuel ratio has deviated from the ideal, and the ECM can immediately adjust the fuel injection duration This rapid correction reduces emission levels because the ECM can more accurately maintain the ideal air/fuel ratio for catalytic converter efficiency Therefore, when observing A/F sensor voltage output, the output is relatively constant because there is no cycling between rich and lean 90 TOYOTA Technical Training Fuel Trim Fuel Systems Slide T874f509, T874f310, Slide T874f508 102 Fuel Trim As the engine and sensors change over time, the ECM needs to adjust fuel injection duration for improved driveability and emission performance Fuel trim is a program in the ECM that allows it to compensate for these changes If the fuel trim value is positive, the ECM concluded that the engine was running lean based on exhaust sensor readings and increased the injection duration to correct the lean mixture If the fuel trim value is negative, the ECM concluded that the engine was running rich and decreased the injection duration to correct the rich mixture • The short-term fuel trim value is the immediate amount of correction the ECM is making when it is in closed-loop fuel control • The long-term fuel trim value is a learned value that is based on the short-term fuel trim correction Long-term fuel trim is part of the engine’s basic injection calculation and is applied during both open and closed loop operation The ECM will learn different long-term fuel trim values for different engine conditions — the engine may require a different amount of correction depending on load and RPM Combined fuel compensation is the sum of short-term fuel trim and longterm fuel trim Techstream displays the current short-term and long-term fuel trim percentages, as well as a total fuel trim number Long-term fuel trim is stored in the ECM’s memory until power is disconnected for several minutes NOTE: Abnormal fuel trim values not necessarily mean the engine is actually running rich or lean Changes in fuel trim mean the ECM had to make corrections to get the engine to run properly Toyota Engine Control Systems I Course 852 91 Fuel Injection Signal Fuel Systems Slide T874f509, T874f310, Slide T874f508 103 Fuel Injection Signal Injection duration, when the injector is turned on and off, can be seen on the oscilloscope wave pattern 92 TOYOTA Technical Training Fuel System Diagnosis Fuel Systems Slide 104 Fuel System When trying to determine the cause of a fuel system concern, use Diagnosis Techstream to check the Freeze Frame data and attempt to duplicate the conditions Use the Technical Information System (TIS) for Repair Manual (RM) and Electrical Wiring Diagram (EWD) information, and look for applicable Technical Service Bulletins (TSBs) Fuel Trim When trying to determine the cause of a fuel trim issue, the most important aspect of diagnosis is to match what the Techstream is reporting to the engine’s actual running condition For example, black spark plugs coupled with positive fuel trims may indicate a feedback issue Verify that the fuel trims are currently abnormal When diagnosing an intermittent condition, check the Freeze Frame data and duplicate the conditions Investigate other DTCs and troubleshoot them first Abnormal cylinder compression, fuel pressure, wrong fuel, spark plug condition, etc., will affect fuel trim On multiple-bank engines, if fuel trim is significantly different between banks, concentrate on things affecting only one bank, such as valve timing, O2 and A/F sensors, or mechanical issues Most types of vacuum leaks or a contaminated MAF sensor will not usually cause an issue on just one bank NOTE: Combined fuel trim is not the same as Total FT on the Techstream Data List Combined fuel trim is the sum of Short FT and Long FT for each bank Total FT is an ECM interpretation of the air/fuel mixture Toyota Engine Control Systems I Course 852 93 Injector Volume Active Test Fuel Systems Slide 105 Injector Volume Active Test If you suspect the O2 or A/F sensors are malfunctioning, verify their response with the Techstream Injector Volume active test This test takes the ECM out of closed loop and allows you to drive the engine rich or lean so you can verify that all the exhaust sensors (O2 and A/F, S1 and S2) are responding properly Keep in mind that the ECM will still use the long fuel trim values during this test Clearing the fuel trims before the active test forces the ECM to run only on the initial injection duration If the engine runs well during this test, it is possible the DTC or driveability condition was caused by an exhaust sensor feedback problem If it still runs poorly, the problem is not likely to be in the feedback system This test can also be helpful in isolating some fuel-trim-related misfire conditions Also keep in mind that if you find a response problem with multiple exhaust sensors, confirm the operation of the shared power and ground circuits The heater circuit must be operating for proper exhaust sensor response Refer to the Repair Manual for detailed O2 and A/F sensor diagnostic procedures and specifications In the illustration above, a large vacuum leak was present While performing an Injector Volume active test and driving the injection volume rich (+24.8%), the A/F sensor (S1) responses were very small (0.3V change) due to the exhaust stream being extremely lean The O2 sensors (S2) stayed at 0.0V because of this extremely lean condition 94 TOYOTA Technical Training Fuel Trim Diagnosis Tips Fuel Systems Slide 106 Fuel Trim Diagnosis Tips A lot can be understood about the engine operating conditions by observing fuel trim readings while increasing engine speed and load For instance: • If combined fuel trim is normal at idle, but increases (+) with engine speed and load, this may indicate a restricted fuel condition, such as low fuel pressure, restricted injectors, restricted fuel filter, etc This may also be caused by a dirty MAF sensor hot wire These issues will usually affect both banks and may cause driveability concerns, such as stalling or hesitation If this condition occurs on only one bank of a two-bank engine, this may indicate restricted injector(s) on the affected bank • If combined fuel trim is high (+) at idle, but decreases (moves closer to 0%) as engine speed and load increase, this may indicate an un-metered air condition such as a vacuum leak This issue will usually affect both banks and may cause driveability concerns, such as a high and/or rough idle If this condition occurs on only one bank of a two-bank engine, this may indicate a vacuum leak or exhaust leak on the affected bank • If combined fuel trim is fixed (+ or -) as engine speed and load increase, this may indicate a stuck A/F or O2 sensor (S1) signal Note: Not all A/F or O2 sensor malfunctions will show up this way This condition will usually only affect one bank and may cause driveability concerns such as smoke from the exhaust pipe (stuck lean), hesitation, etc Toyota Engine Control Systems I Course 852 95 Fuel Systems 96 TOYOTA Technical Training ... failure Toyota Engine Control Systems I Course 852 85 Fuel Cut Fuel Systems Slide Slide97 T874f509, T874f310, T852f229 T874f508 Fuel Cut The ECM controls fuel delivery differently according to engine. .. speed while the engine is starting Toyota Engine Control Systems I Course 852 75 Fuel Pump Controls: 3-Speed Control with Fuel Pump ECU Fuel Systems Slide 86 T852f139/T852f194 3-Speed Control with... switch for at least one second Toyota Engine Control Systems I Course 852 77 Vacuum Pressure Regulator Fuel Systems Slide Slide88 T874f509, T874f310, T852f201/T852f202 T874f508 Fuel Pressure Fuel

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