Component Tests and General Diagnostics

Fig. 2 LH-Jetronic II fuel injection system wiring diagram.:

Fig. 3 LH-Jetronic II fuel injection system wiring diagram.:

Fig. 4 LH-Jetronic II fuel injection system wiring diagram.:

Fig. 5 LH-Jetronic II fuel injection system wiring diagram.:

Refer to Figs. 2 through 5 during system test procedure.

Fig. 2 LH-Jetronic II fuel injection system wiring diagram.:

Fig. 6 Temperature sensor operating specifications:

1. Check fuses, connectors and grounds as follows:
a. Ensure that blade fuse in engine compartment is satisfactory.
b. Ensure that gray wire to ignition coil terminal No. 1 is securely connected.
c. Ensure that electrical connectors at injectors, temperature sensor, air control valve, throttle valve switch and air mass meter are securely connected.
d. Ensure that ground connections are properly tightened and have good contact.
2. Check air intake system for leakage as follows:
a. Hose between air mass meter and intake manifold.
b. All hoses and connections to intake manifold.
c. Joints for intake manifold and throttle valve housing.
3. Check throttle valve switch adjustment by opening throttle valve slightly and listening to switch. A click should be heard the moment the throttle valve moves.
4. Adjust throttle valve switch, if necessary, as follows:
a. Loosen switch retaining screws.
b. Turn switch slightly clockwise, then counterclockwise until click is heard.
c. Tighten screws, then check operation.
5. Check fuel pump and tank pump as follows:
a. Remove panel on right side under dashboard, then disconnect three prong connector.
b. Connect a jumper wire between blue/red and blue/yellow wires in connector.
c. Turn ignition switch to ``On'' position and ensure that pumps run. Main fuel pump operation can be felt by manually feeling fuel line pulsations. Tank pump operation can be heard by removing fuel filler cap and listening in filler tube.
d. Turn ignition switch to ``Off'' position.
e. If neither pump operates, check fuse No. 12 and wiring.
If. If tank pump does not operate, check fuse No. 5, pump wiring and pump.
g. If fuel pump does not operate, check pump wiring and pump.
6. With ignition switch in ``Off'' position, connect pressure meter 5011 or equivalent between fuel line and injection manifold using hose 5116 and nipple 5265, or equivalents.
7. Plug unused meter hose using plug 5266 or equivalent, then move meter handle to flow through position.
8. Turn ignition switch to ``On'' position and check line pressure. Line pressure should be 35.5 psi.
9. If line pressure is too high, proceed as follows:
a. Turn ignition switch to ``Off'' position.
b. Disconnect fuel return line from pressure regulator and blow in line. If line is open, replace pressure regulator and measure pressure again.
10. If line pressure is too low, proceed as follows:
a. Manually pinch off fuel return line and check if pressure rises. Do not let pressure exceed 85.2 psi.
b. If pressure rises quickly, replace pressure regulator and measure pressure again.
c. If pressure rises slowly, fuel filter, tank pump filter or line is blocked.
d. If pressure does not rise, fuel pump is defective.
11. Check line pressure regulator function as follows:
a. Connect vacuum pump to line pressure regulator.
b. If line pressure does not decrease when pressure regulator is evacuated, replace line pressure regulator.
c. Remove vacuum pump and connect hose at regulator.
12. Turn ignition switch to ``Off'' position, place cloth under fuel line, remove meter and nipple and connect fuel line to injection manifold.
13. Connect three prong connector under right side of dashboard.
14. With ignition switch in ``Off'' position, remove panel in passenger compartment in front of right front door, then disconnect electrical connector at control unit.
15. Connect ohmmeter between ground and terminals 11 and 25 on control unit connector. If resistance is not zero ohms, check ground contacts at intake manifold.
16. Turn ignition switch to ``On'' position and connect a voltmeter between ground and terminal 18. If meter does not show battery voltage, check system wiring. Turn ignition switch to ``Off'' position.
17. Ensure that shielding wires are twisted together and connected to terminal 5.
18. Check fuel pump relay as follows:
a. Turn ignition switch to ``On'' position.
b. Ground terminal 17.
c. If fuel pump does not start, replace fuel pump relay.
d. Turn ignition switch to ``Off'' position.
19. Check [1][2]system relay as follows:
a. Connect voltmeter between ground and terminal 9.
b. Ground terminal 21.
c. If meter does not show battery voltage, replace [1][2]system relay.
20. Check air mass meter current supply and ground as follows:
a. Ground terminal 21.
b. Peel back rubber boot from around air mass meter wiring connector.
c. Connect voltmeter between terminal 9 of air mass meter (orange wire), Fig. 2, and ground, then between terminals 9 and 36 (black wire) of air mass meter. If meter does not show battery voltage, replace air mass meter.
d. Reposition rubber boot around air mass meter wiring connector.
21. Check starter motor wiring as follows:
a. Connect voltmeter between ground and terminal 4.
b. Crank starter. If meter does not show battery voltage, check starter wiring.
22. Check ignition coil wiring as follows:
a. Turn ignition switch to ``On'' position.
b. Connect voltmeter between ground and terminal 1. If meter does not show voltage, check ignition coil wiring.
c. Turn ignition switch to ``Off'' position.
23. Check injectors as follows:
a. Connect ohmmeter between pump relay terminal 87 and control unit connector terminal 13.
b. If meter reads approximately 5.3 ohms, either an injector or injector wire is defective.
c. If meter reads approximately 8 ohms, two injectors or injector wires are defective.
d. If meter reads approximately 16 ohms, three injectors or injector wires are defective.
e. If defective, remove injector connectors and check each injector separately. Resistance for each injector should be 16 ohms.
24. Check temperature sensor as follows:
a. Connect ohmmeter between ground and terminal 2.
b. If test values are not within specifications, Fig. 6, temperature sensor may be defective.
c. Extremely high test values indicate an open circuit in temperature sensor or wiring. Check temperature sensor ground at intake manifold.
d. Zero resistance indicates a short circuit.
25. Check air mass meter as follows:
a. Connect ohmmeter between terminals 6 and 7 of control unit connector, then 6 and 14.
b. If resistance between terminals 6 and 7 is not 3.7 ohms, or resistance between terminals 6 and 14 is not 0-1000 ohms, replace air mass meter.
26. Check throttle valve switch as follows:
a. Connect ohmmeter between ground and terminal 3, then depress accelerator pedal.
b. Meter should read zero ohms in idle position and infinite ohms in other positions.
c. Connect ohmmeter between ground and terminal 12. Meter should read zero ohms in full throttle position and infinite ohms in all other positions.
d. If meter does not read as described, check throttle valve switch ground at intake manifold. If ground is satisfactory, replace throttle valve switch.
27. Check air control valve as follows:
a. Connect ohmmeter between pump relay terminal 87 and control unit connector terminal 10, then between pump relay terminal 87 and control unit connector terminal 23.
b. If ohmmeter does not read approximately 20 ohms for either check, replace air control valve.
28. Check air conditioning microswitch as follows:
a. Connect ohmmeter between ground and terminal 16, then turn knob on air conditioning control panel.
b. If resistance does not decrease, replace air conditioning microswitch.
29. With ignition switch in ``Off'' position, install control unit connector cover and plug in control unit connector.
30. Peel back rubber cover from around injector wires of one injector and connect voltmeter positive lead to yellow/red wire of injector and voltmeter negative lead to green/white wires of injector, then set voltmeter to read 0-4 volts.
31. Disconnect connectors at injectors and the electrical connector at the temperature sensor.
32. Crank starter while observing meter deflection. Deflection should be large at initial cranking and then decrease.
33. Connect electrical connector at temperature sensor, then crank starter while observing meter deflection. Meter should deflect as in step 32 but with decreased deflection.
34. If meter deflection is not as described in steps 32 and 33, replace control unit.
35. Connect electrical connectors at injectors.
36. Start engine and run until it reaches operating temperature.
37. If voltmeter deflection does not decrease slightly as engine warms up, replace control unit.
38. Shut off engine and connect tachometer, then start engine.
39. Ensure that idle speed is 750 RPM, adjusting as necessary.
40. Turn on air conditioning and note whether engine speed increases to 900 RPM, then turn off air conditioning.
41. If idle speed does not increase, check that air control valve is not sticking by installing new air control valve and repeating steps 39 and 40.
42. If engine does not idle, check air mass meter as described in step 25.
43. Disconnect electrical connector at temperature sensor and check whether idle speed increases to 1600-2500 RPM, then connect electrical connector at temperature sensor and note whether engine speed returns to normal idle.
44. If idle speed does not react as described in step 43, replace control unit.
45. Slowly increase engine speed. If meter deflection does not increase with engine speed, check voltage from air mass meter as follows:
a. Turn off engine.
b. Peel back rubber cover from air mass meter electrical connector.
c. Connect positive voltmeter lead to terminal 7 (white/red wire) and negative voltmeter lead to terminal 6 (green/yellow wire), then start engine.
d. If voltage increases as engine speed increases, replace control unit.
46. Connect voltmeter as described in step 30.
47. Quickly increase engine speed. If deflection is not large at first and then decreases slightly, replace control unit.
48. Increase engine speed to above 2000 RPM, then quickly release throttle control.
49. If meter deflection does not drop to zero until engine speed falls to approximately 1400 RPM and then show deflection again, replace control unit.
50. Disconnect electrical connector at throttle valve switch and increase engine speed to at least 3500 RPM.
51. Connect a jumper wire between terminals 18 and 3 of throttle valve switch.
52. If meter deflection does not increase slightly, replace control unit.
53. Connect electrical connector at throttle valve switch.
54. Turn off engine, then disconnect voltmeter from injector and reposition rubber cover at injector connector.
55. Peel back rubber cover from air mass meter electrical connector.
56. Connect voltmeter positive lead to terminal 8 (white wire) and negative lead to terminal 36 (black wire).
57. Start engine and increase engine speed to above 2000 RPM, then turn off engine.
58. If, after approximately 5 seconds, voltmeter does not show approximately 1 volt for 1 second, replace control unit.
59. Disconnect voltmeter and reposition rubber cover around air mass meter electrical connector.
60. Install panels under dashboard.