1989 Volvo 760 Repair Question
1989 Volvo 760 car dies ...when ac not on during drive and
1989 Volvo 760 4 cyl Two Wheel Drive Automatic 118200 miles
Bought car used just discovered car dies when ac is not on. Is idle adjustable? Hard starts after sitting starts right up after turning off. Fuel filter? I don't know so please let me know
COMPUTERIZED ENGINE CONTROLS
All models use a multi-point electronic fuel injection system with an electronic ignition system using computer controlled timing. Depending upon application, the systems are either a Bosch LH-Jetronic (hot wire) or a Bendix supplied Regina unit. Both systems have self-diagnostic capabilities with a integral diagnostic unti for testing.
Both systems use an Electronic Control Unit (ECU) receiving input from engine monitoring sensors. These sensors include; coolant temperature sensor, oxygen sensor, mass airflow meter (Bosch), intake air temperature sensor (Regina) and pressure sensor (Regina). The ECU uses these input signals to control air/fuel mixture for emission control, fuel economy and good drivability.
Ignition control is provided by a separate ignition ECU. Vehicles using Bosch fuel injection are equipped with a Bosch EZK ignition system. Vehicles using Regina fuel injection use a Rex 1 ignition system. Both systems have self-diagnostic capabilities and use the same diagnostic unit as the fuel injection system for testing.
All vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input usage on a specific model, see WIRING DIAGRAMS article. The available input signals include the following:
A/C Compressor/A/C Switch -- Signals fuel injection ECU of A/C operation. This allows fuel injection ECU to control idle speed with the idle valve.
Air Temperature Sensor (Regina) -- Information gathered from air temperature sensor is combined with information from pressure sensor to calculate intake air mass.
Coolant Temperature Sensor -- Coolant temperature sensor is a negative temperature coefficiency type, meaning its resistance lessens as temperature increases. The sensor unit has 2 resistors. One resistor is connected to fuel injection ECU and the other resistor is connected to the ignition ECU.
Detonation (Knock) Sensor -- The knock sensor(s) detect knocking and send signal to ignition ECU. The ECU is able to gradually retard ignition timing to each individual cylinder. If knocking does not stop, a signal is sent to fuel injection ECU to enrich the air/fuel mixture.
Fuel Injection Control Unit -- The fuel injection ECU serves as an input device for ignition calculation. Fuel injection ECU provides information on engine load, throttle position, etc.
Hall Effect Sensor (Turbo) -- The Hall Effect generator (sensor) is mounted in the distributor on turbocharged models. This sensor supplies the ignition ECU with an engine speed and crankshaft position signal.
Ignition Control Unit -- The ignition ECU serves as an input device for fuel injection calculation. Ignition ECU provides information on engine speed, crankshaft position, knocking, etc.
Manifold Absolute Pressure Sensor (Regina) -- Also called the pressure sensor, this sensor measures both atmospheric and manifold absolute pressure. This sensor is connected by a hose to intake manifold. The ECU can calculate intake air mass from these inputs.
Mass Airflow Meter (Bosch) -- This meter measures intake air mass. Measure sensor is a heated wire which is maintained at 250 °F (120 °C) hotter than intake air. The fuel injection ECU is able to calculate mass of intake air by measuring amount of current required to maintain wire teperature. When engine is turned off, any dirt on the wire is burned off by heating the wire to above 1800 °F (1000 °C).
Oxygen Sensor -- Also known as a Lambda-sond, this heated oxygen sensor generates an electrical signal dependant upon fuel/air mixture. Fuel injection ECU uses this information to adjust amount of injected fuel.
P/M Generator (Except Turbo) -- The permanent magnet generator, also called a fixed impulse sensor, generates an engine speed and TDC signal. This sensor is located at rear of engine block and senses markings (drilled holes) in the flywheel. There are no holes drilled at 2 pairs of the markings. These are 90 degrees before TDC for cylinders No. 1 and 4.
Throttle Switch -- This switch signals ignition and fuel injection ECUs when throttle is fully closed or fully open.
ELECTRONIC IGNITION SYSTEM
The electronic ignition system controls triggers the ignition coil using signals from the ECU based on crankshaft position, engine speed, vehicle speed, and inputs from fuel injection ECU. Turbo models use a Hall Effect sensor, located in the distributor, to determine crankshaft position and engine speed. All other models use a flywheel sensing permanent magnet generator to determine crankshaft position and engine speed. The ignition coil receives battery voltage through the fuse panel and is grounded through the power stage (power transistor). When the ECU is signaled of proper crankshaft position, the power stage removes the ground from the coil, firing the plug.
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