Checking injection nozzles
If you have a suspicion that one of the injectors is not working, it is easy to check with an LED voltmeter and an accurate ohmmeter.
Disconnect plugs from all injection nozzles.
Voltage Test First: LED Voltmeter (not a control lamp) connect to the plug contacts of the plug. Start the engine: the LEDs in the voltmeter must flicker, otherwise there is no power supply or the connection is faulty «mass» Control block. This check cannot be carried out with a conventional measuring instrument.
Resistance check: disconnect the plugs of the injection injectors, connect an ohmmeter to both contacts of the injector: on a cold engine, it should show 13.5-17 ohms.
With plug removed (1) you can check the power supply to the injection nozzles using an LED voltmeter (2). When the engine is cranked with the starter, the LEDs in the voltmeter should flicker. Otherwise, there is no submission of the scripture.
If the indicator is outside the specified limits, replace the nozzle (if the measurement was accurate).
Leak test: remove the fuel distributor together behind the injectors.
The injection nozzle plugs are removed, the fuel lines remain connected.
Have an assistant crank the engine several times using the starter to start the fuel pump and build up operating pressure.
Watch the injection nozzles: each individual nozzle should lose no more than 1-2 drops of fuel per minute. Otherwise, the leaky injector must be replaced.
Regardless of this, it is possible to check the injection stream and the injection quantity of the injector, in case this is necessary due to engine interruptions.
Throttle Potentiometer
Disconnect the plug of the throttle valve potentiometer.
Using an accurate ohmmeter, measure the resistance between the potentiometer contacts.
It is necessary to measure in the positions of the throttle valve «idling» And «full load» when the engine is not running.
The ohmmeter should show the following standard indicators:
Air mass meter (MPI only)
Push back the rubber tip of the air mass meter, leave the plug connected.
Connect an accurate voltmeter from the back to the plug contacts, according to the described scheme:
Measurement 1: connect the connecting wire to pins 2 and 3. Switch on the ignition.
The voltmeter should show 12-14 V. Otherwise, the electricity supply is faulty.
The 2.8-liter engine has an air mass meter in the engine compartment on the right rear (arrow), flanged to the air filter housing.
Check fuse no. 27, if necessary check wire from fuse no. 27 to plug 3 of the air mass meter.
Or check the connection to the motor housing (contact 2).
Measurement 2: connect the connecting wire to pins 2 and 4.
Turn on the ignition.
The voltmeter should show 1.0-7.5 V. Otherwise, there is a defect in the CO-potentiometer in the air flow meter. Replace air mass meter.
Measurement 3: connect the connecting wire to pins 1 and 2.
Turn on the ignition.
The voltmeter should show 0.3-1.1 V.
Start the engine (wire stays connected) Turn off all electrical consumers, make sure that the cooling system fan does not work.
Constantly change the engine speed between idle and 4000 rpm.
The voltmeter should show (depending on speed) between 1.5 and maximum 3.4 V. Otherwise, the air mass meter is defective. Replace.
Idle speed stabilization valve (MPI only)
The speed stabilization valve for the 2.8-liter engine is located on the right side of the throttle body. It is checked like this:
Disconnect the plug of the idle speed stabilization valve and connect an accurate ohmmeter to both plug contacts of the valve.
The device should show 7-11 ohms, otherwise the valve is faulty.
Further check of action: to remove the valve of stabilization of idling; plug remains connected. Move the rotating piston in the air hole in the valve to the position «open» or «closed» (do not use metal tools!).
Turn on the ignition. The rotating piston should be approximately in the middle position.
Check the ease of movement of the rotating piston: it can be set in motion by abruptly turning the valve removed.
In addition, the piston must be free of friction marks or grooves.
Idle speed stabilization valve (MPFI only)
Attention! The idling stabilization valve of the 2.6-liter engine cannot be dismantled with improvised means, because after re-installation, the so-called basic adjustment of the injection system becomes necessary, and this can only be done using the VAG 1551 fault memory reader in the Audi workshop.
In addition: if the plug of the idle speed stabilization valve is disconnected before one and a half hours have elapsed after the last stop of the engine, then a malfunction is recorded in the fault memory «Faulty idle speed control valve» (which may not be true at all). You can only check the winding on this valve:
Disconnect the idle speed control valve plug.
Measure the resistance between valve plugs 1 and 4 and 2 and 3 with an accurate ohmmeter.
If the valve is in good condition, the resistance should be 45-60 0m, respectively, otherwise the valve should be considered faulty.
Further checks with home remedies are not possible.
If the workshop replaces the valve, then at the same time it carries out the said basic adjustment.
Different types of idle speed stabilization valve. On the left is a 2.6-liter engine, on the right is a 2.8-liter.
The engine coolant temperature sensor is located on the rear left of the engine (screwed into the coolant hose) for ignition/injection system (arrow). The diagram shows the resistance value of the sensor as a function of temperature.
Attention! If the plug of the coolant temperature sensor of the model with a 2.6-liter engine is disconnected before one and a half hours after the engine has stopped running, then the following is written to the memory of the fault memory: «Faulty coolant temperature sensor» (which may not be true at all).
General note: The temperature sensor can cause the engine to malfunction in certain temperature ranges. Examination:
Disconnect the coolant temperature sensor connector.
Using an accurate ohmmeter, measure the resistance between both sensor plugs.
Compare the obtained test result with the standard values in the diagram above, depending on the temperature of the coolant. If the indicator strongly deviates from the standard, replace the temperature sensor.
In addition, two more average resistance indicators: at 20°C coolant temperature, the resistance should be approximately 2.5 kOhm, at 80°C - approximately 330 Ohm.
Intake air temperature sensor (MPFI only)
Attention! If the plug of the intake air temperature sensor is disconnected before one and a half hours after the engine stops running, then the following is written to the memory of the drive: «Faulty intake air temperature sensor» (which may not be true at all).
Disconnect intake air temperature sensor plug.
Using an accurate ohmmeter, measure the resistance between both sensor plugs.
Compare the obtained test result with the standard values in the diagram below, depending on the intake air temperature. If the indicator strongly deviates from the standard, replace the temperature sensor.
As an addition, another average resistance value: at 20°C (room temperature, cold engine) the resistance should be approximately 6.3 kΩ.
Checking the lambda probe
For this test, the plug connection in the wiring to the lambda probe must be disconnected. The plug connections to the left and right probe are shown in the illustration on the next page.
Checking is done using an accurate ohmmeter:
Checking the special heater: Disconnect the plug for the lambda probe heater.
The standard indicator for proper heating is 3-15 ohms.
Otherwise, replace the lambda probe.
Checking the lambda probe: disconnect the plug to the lambda probe (calibrated wire).
Connect an ohmmeter to the plug contacts, to the probe to the motor housing.
Standard indicator with a working probe: ∞ Ohm.
Otherwise, replace the lambda probe.
Checking the line to the control unit: disconnect the plug from the lambda probe (calibrated wire) (as already done).
Connect a voltmeter to the contacts of the plug to the control unit and to the engine housing.
With good wiring, the indicator should be 0.35-0.45 V.
Otherwise, check the wiring.
If the wiring is OK, replace the control unit.
Replacing the lambda probe
Disconnect the wire ends, loosen the cable bandages.
Lubricate the thread with mounting paste before installing the probe. The paste must not get into the slot of the probe.
Tightening torque: 50 Nm.
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