Pic. 14.8. Elements of the air supply system of the PBT system: 1 - expansion chamber; 2 - damper; 3 - throttle assembly; 4 - throttle position sensor; 5 - solenoid valve for engine heating in idle mode; 6 - solenoid valves (for air conditioner); 7 - temperature sensor of the air entering the engine; 8 - air flow meter; 9 - air valve
Pic. 14.9. Elements of the fuel supply system of the RVT system: 1 - fuel pump; 2 - pressure regulator; 3 - fuel filter; 4 - distribution fuel line; 5 - nozzles; 6 - pressure regulator; 7 - fuel tank
The PBT system is essentially a Bosch L-Jetronic fuel injection system. The main elements of this system are shown in fig. 14.8 and 14.9.
Air flow meter
The air flow meter measures the amount of air entering the engine and, using a potentiometer, converts it into an electrical signal sent to the control unit.
The air flow meter is equipped with an air intake temperature sensor, an idle bypass system, and a fuel pump switch.
Checking the air flow meter
Turn out bolts of fastening of a clamping plate and remove a rubber casing from a socket of a counter of an expense of air.
Turn the ignition on and use a voltmeter to measure the voltage between each pin of the connector and «weight» car. On contacts «FC» And «VB» there should be battery voltage, on the contact «VC» – voltage 6–10 V, on the contact «VS» - 0.7–2.7 V.
If the measured voltages differ, check the condition of the wires and the fuse.
Release the clips and disconnect the connector from the air flow meter.
Pic. 14.10. PBT Air Flow Meter Connector Contacts
Ohmmeter connected between contacts «E2» And «VS» connector, check the resistance, which should be more than 20 ohms (pic. 14.10). Contact resistance «E2» And «VC» should be 100-300 ohm, between contacts «E2» And «VB» – 200-400 ohm and between contacts «E1» And «FC» it should be infinity.
Pic. 14.11. Using a hair dryer to heat the inside of the air filter
Contact resistance «E2» And «TNA» depends on the temperature of the air in the air filter. Remove the air filter cover and using a thermometer and heat source (e.g. hair dryer) measure the resistance and compare it with the technical data (pic. 14.11).
Open the inner plate of the air flow meter and measure the resistance between the contacts «E2» And «VS», which should be less than 400 ohms. Between contacts «E1» And «FC» resistance should be zero.
Check that the inner plate moves freely and, if necessary, use compressed air to remove deposits and particles that are preventing the plate from moving.
Replace the air filter cover and connect the connector.
Removal and installation of the air flow meter
Turn out bolts of fastening of a pressure plate and disconnect a socket from an air flow meter.
Loosen the clamps and disconnect the main air hose and the two air supply hoses.
Disconnect the vacuum hoses going to the power steering or the air conditioning solenoid valves.
Remove the air filter cover, then unscrew the air flow meter mounting bolts and remove the rubber seal.
Installation is carried out in the reverse order of removal. Install a new rubber seal and after installation, check and adjust the engine idle speed.