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. 6 Temperature sensor operating specifications:

1. Check fuses, connectors and grounds as follows:
a. Ensure that fuse No. 1 and 11 are satisfactory.
b. Ensure sensor electrical connectors are not interchanged.
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 satisfactory 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 above foot pedals, then disconnect electrical connector located next to charge air overpressure switch.
b. Ground connector yellow/black wire using a suitable jumper.
c. Turn ignition switch ``On'' to start fuel pumps. Pumps should be clearly heard.
d. Turn ignition switch to ``Off'' position.
e. Pull out electrical unit from center console, then remove [1][2]system relay.
If. Turn ignition switch to ``On'' position and check for voltage at terminal 30. If voltage is not present, check wire and fuse No. 1 between battery and relay.
g. Connect jumper wire across terminals 30 and 87/2. Both pumps should start. If pumps do not start, check wires between relay and pumps.
h. Check circuit between terminals 87/1 and 85, then ensure terminals 86/1 and 86/2 are properly grounded.
i. Test pumps with new relay.
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 36 psi for non-turbo engines or 42 psi for turbo engines.
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 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 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. Disconnect jumper wire and connect pressure switch.
14. Check charge air overpressure switch, if equipped, as follows:
a. Connect pressure tester and pressure gauge 5230 or equivalent to hose at intake manifold.
b. Connect suitable buzzer to switch, then increase pressure with pump. Switch should stop buzzing at 12-14 psi. Replace switch as required.
c. Disconnect pump and pressure hose.
15. With ignition switch in ``Off'' position, remove panel in passenger compartment in front of right front door, then disconnect electrical connector at control unit. When checking connector, do not insert tester probe into front of connector. Check terminals in holes through side of connector.
16. Connect ohmmeter between ground and terminals 5, 11, 19 (1987-88 B230F) and 25 on control unit connector. If resistance is not zero ohms, check ground contacts at intake manifold.
17. Ensure Lambda-Sond shielding wires are connected to terminal 5.
18. Connect ohmmeter between ground and terminals 12 and 22. Resistance should be infinite for both terminals.
19. Check engine speed signal from ignition system control unit by connecting suitable tachometer between ground and terminal 1, then engage starter. Tachometer should show engine speed.
20. Turn ignition switch to ``On'' position, then connect voltmeter between terminal 18 and ground. Battery voltage should be present.
21. Check main relay as follows:
a. Turn ignition switch ``Off'', then connect voltmeter between terminal 9 and ground.
b. Ground terminal 21 using a suitable jumper wire. Relay should complete circuit and meter should read battery voltage.
22. Check pump relay as follows:
a. Ground terminal 21 to complete main relay circuit.
b. Ground terminal 17 and listen for fuel pump operation.
c. Connect voltmeter between terminal 18 of 20 pole connector on 1985-86 models or 35 pole connector on 1987-88 models (located next to A pillar) and ground. Battery voltage should be present.
d. Disconnect ground leads.
23. Separate black retainer containing three connectors located at the right A pillar.
24. Check injectors and ballast resistors as follows:
a. Connect ohmmeter between terminal 13 on control unit and terminal 18 of 20 pole connector for 1985-86 models or terminal 9 on 35 pole connector for 1987-88 models. Resistance should be approximately 2-4 ohms.
b. If resistance is not as specified, measure each injector and ballast resistor separately. Injector resistance should be 2 ohms. Ballast resistance should be 6 ohms.
25. Check air control valve as follows:
a. Connect ohmmeter between terminal 18 of 20 pole connector for 1985-86 models or terminal 9 of 35 pole connector for 1987-88 models and terminals 23 and 10 on control unit.
b. Resistance should be approximately 20 ohms in both cases.
26. Check preheating resistor in Lambda-sond as follows:
a. Connect ohmmeter between ground and terminal 18 of 20 pole connector.
b. With Lambda-sond cold, resistance should be 3 ohms. With Lambda-sond warm, resistance should be 13 ohms.
27. Connect 20 pole connector at right A pillar.
28. Check coolant 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.
29. Check throttle switch as follows:
a. Connect ohmmeter between ground and terminal 3. Resistance should be 0.
b. Depress accelerator pedal slightly. Resistance should increase to infinity. Ensure throttle switch ground is connected to intake manifold.
30. On early 1985 models with manual transmission, check transmission switch as follows:
a. Connect ohmmeter between terminal 15 and ground.
b. With gear selector lever in 1st or 2nd, resistance should be 0. With gear selector in 3rd or 4th, resistance should be infinite.
31. On all models, check air mass meter as follows:
a. Connect connector on LH control unit. Do not assemble connector.
b. Move rubber cover on air mass meter to one side.
c. Connect ohmmeter between terminal 1 and ground, then between terminal 2 and ground. Resistance should be less than 1 ohm in both cases.
d. Check wiring continuity if value is higher.
e. Turn ignition switch to ``On'' position, then connect voltmeter between terminal 5 and ground. Meter should read battery voltage.
If. Check wiring continuity and fuel system relay if battery voltage is not present.
g. With ignition switch in ``On'' position, connect voltmeter between terminal 14 at LH control unit and ground.
h. Turn CO screw on air mass meter to maximum lean position. Voltmeter should read 0 volts.
i. Turn CO screw on air mass meter to maximum rich position. Voltmeter should read 2.6 volts.
j. If voltage is not present or there is no voltage variation when screw is turned in steps h and i, check wiring continuity. Adjustment screw should be resealed after adjustment.
k. Connect voltmeter between terminal 7 at LH control unit and ground. Meter should read approximately 1.2 volts.
l. Start engine and allow to reach normal operating temperature.
m. With engine idling, meter should read approximately 2.2 volts. Increase idle speed to 3500 RPM. Output voltage should increase to approximately 2.9 volts.
n. Check wiring continuity if voltage is not as specified.
o. With engine idling, connect voltmeter between terminal 4 and ground, then increase engine speed to 2500 RPM.
p. Close throttle and allow engine to return to idle, then turn ignition switch to ``Off'' position. After approximately 4 seconds, meter should deflect for 1 second.
q. If meter does not deflect, check wiring continuity.
r. Reinstall rubber boot over air mass meter electrical connector.
32. Check signal from A/C control panel as follows:
a. Connect voltmeter between ground and terminal 16, then start engine.
b. Move control to A/C On position. Voltmeter should read battery voltage and idle speed should increase to 900 RPM.
33. Turn ignition switch to ``Off'' position, then connect control unit electrical connector.
34. Start engine. If engine does not start, test with a new control unit.
35. Connect suitable CO meter to adapter next to catalytic converter, then allow engine to reach normal operating temperature. CO meter adapter may be very hot.
36. Check Lambda-sond as follows:
a. Disconnect Lambda-sond connector, then ground wire leading to control unit. CO should increase to ensure that wire and control unit are satisfactory.
b. Connect voltmeter to Lambda-sond. CO meter should deflect to show that Lambda-sond is functioning. If CO meter deflects, voltage should be approximately 0 volt.
c. Connect Lambda-sond connector.
37. Check and adjust CO content as follows:
a. Connect test diode 9995280-6 green/white wire to test point located at right wheel housing and diode red wire to battery positive terminal.
b. Connect suitable tachometer and analyzer, then allow engine to reach normal operating temperature.
c. Ensure idle speed is at approximately 750 RPM. If idle speed is not as specified, check air control valve hoses for blockages.
d. Test diode should flash if CO is satisfactory. If test diode remains On, CO is too high (rich air/fuel mixture). If test diode remains Off, CO is too low (lean air/fuel mixture).
e. If CO level is not as specified, turn ignition switch to ``Off'' position.
If. Drill two .08 inch holes in CO adjusting screw plug, then remove plug using suitable pliers.
g. Start engine, then turn CO adjusting screw until diode starts to flash. Turning screw counterclockwise reduces CO and clockwise increases CO.
h. Seal CO adjusting screw using a new plug.
38. If not faults are found during system test procedure and engine is running rough, install new control unit.