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Home >> Volvo >> 1987 >> 780 AW71L >> Repair and Diagnosis >> Engine Performance >> System >> Fuel Injection System - BOSCH LH (Non Turbo) >> Testing >> System Check

System Check

NOTE: The following system check applies to vehicles with 2.3L engines only.
  1. Peel back rubber cover from around one injector. Connect positive lead of a voltmeter to Yellow/Red wire, and negative lead to Green/White wire. Set meter on low scale (0-4 volts).
  2. Remove connectors from all injectors so that engine does not start. Remove connector from temperature sensor to simulate cold start.
  3. Crank engine and check meter deflection. Deflection should be large when first cranking and then decrease. Connect temperature sensor. Crank engine. Voltmeter should deflect as before but with decreased deflection. Plug in injector connectors.
  4. Start engine and observe meter as engine warms up to operating temperature. If enrichment function is working properly, meter deflection should decrease slightly as engine warms up. Turn ignition off.
  5. Connect a tachometer to engine. Start engine. Idle speed should be 750 RPM. Turn on air conditioning. Idle speed should increase to 750 RPM. If idle does not increase, check air control valve operation. If idle does increase check mass air meter.
  6. To check fast idle function, unplug temperature sensor connector while engine is idling. Engine speed should increase to 1600-2500 RPM. Connect temperature sensor and check engine RPM. Engine speed should return to normal idle.
  7. Slowly increase engine speed. Voltmeter deflection should increase with engine speed. If not, check voltage signal from air mass meter.
  8. Turn off ignition. Peel back rubber cover from air mass meter connector. Connect voltmeter positive lead to terminal No. 7 and negative lead to terminal No. 6. Start engine. Voltage should increase as engine speed increases. Replace and test with new control unit if air mass meter is okay.
  9. With voltmeter still connected to injector, check acceleration enrichment. Quickly increase engine speed. Meter deflection should at first be large and then reduce slightly.
  10. To check fuel shut-off during engine braking, increase engine speed to 2000 RPM. Quickly release throttle control. Meter deflection should go down to zero until speed reduces to approximately 1400 RPM. At 1400 RPM, meter should show deflection again.
  11. To check full throttle enrichment, unplug connector from throttle valve switch. Engine speed will increase slightly. Increase engine speed to at least 3500 RPM. Connect a jumper wire between connector terminals No. 18 and 3. Meter deflection should increase slightly. Reconnect throttle valve switch.
  12. Turn off engine. Remove voltmeter from injector. To check air mass meter measuring wire dirt burn-off, peel back boot from air mass meter connector. Connect a voltmeter to terminals No. 8 and 36.
  13. Start engine and increase engine speed to 2000 RPM. Release throttle, let engine return to idle, and turn ignition off. After approximately 4-5 seconds, voltmeter should show about one volt for one second.
  14. Remove voltmeter. Reposition rubber boots around air mass meter and injector wiring connectors.
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