INTRODUCTION
Before testing separate components or systems, perform basic diagnostic procedures in BASIC TESTING article. Since many computer-controlled and monitored components set a trouble code if they malfunction, also perform self-diagnostics in TESTS W/CODES article.
Note. Testing individual components does not isolate shorts or opens. Perform all voltage tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter to isolate wiring harness shorts or opens.
TESTING PRECAUTIONS
- Turn ignition off or disconnect battery for resistance tests. Disconnect engine speed/reference mark sensor for compression tests, otherwise, high voltages and insulation damage to ignition coil, high-voltage distributor and ignition leads may result.
- DO NOT connect a capacitor to ignition coil terminals. DO NOT connect ignition coil terminal No. 1 to ground. Ignition coil and DME control unit could be damaged.
- DO NOT connect battery leads or test light to ignition coil terminal No. 1. DME control unit will be damaged. DO NOT disconnect ignition lead from ignition coil secondary terminal during engine operation.
- Avoid voltage flashover from ignition coil secondary terminal to ignition coil primary terminals (No. 1 and 15), or DME control unit may be damaged.
- During testing, secondary circuit of ignition system must be suppressed at all times with 4000-ohm resistance (1000-ohm distributor cap suppression resistor; 3000-ohm spark plug lead suppression resistors).
- Always turn ignition off or disconnect battery before disconnecting ignition or DME control unit connectors. Electrostatic discharge may damage DME control unit.
- DO NOT disconnect battery while engine is running. Reversed battery polarity could damage ignition or DME control unit. DO NOT exceed a charging voltage of 16 volts (including when using a battery charger).
COMPUTERIZED ENGINE CONTROLS
Note. See TESTS W/CODES article in the ENGINE PERFORMANCE section for diagnosis and testing of computerized engine control components.
Scheme 2
ENGINE SENSORS & SWITCHES
Note. For engine sensor and switch circuits not listed, see TESTS W/CODES article for diagnosis and testing procedures.
Scheme 3
- This sensor can only be tested using an oscilloscope. To do so, set-up and adjust oscilloscope using manufacturer instructions.
- Disconnect DME control unit. Connect positive test lead to terminal No. 47 (White wire) and negative lead to terminal No. 48 (Brown wire) of DME control unit wiring harness connector. Crank engine and observe reading.
- Oscillations of at least 3 volts and an intermediate higher amplitude (reference mark) signal must be displayed. (Scheme 3) If necessary, connect oscilloscope leads to terminal No. 1 (White wire) and terminal No. 2 (Brown wire) at sensor.
- If voltage reading is less than 3 volts, distance between sensor and ring gear may be incorrectly adjusted. Adjust sensor until air gap between ring gear and sensor is 0.04" (1 mm).
- To check air gap on vehicles with Tiptronic (automatic) transmission, remove right rear wheel and heater hose from heat exchanger. Remove engine speed sensor. (Scheme 4)
- Align a flywheel tooth to center of sensor opening. Measure ring gear tooth depth and sensor length. Difference between ring gear tooth depth and sensor length must be 0.03-0.05" (0.8-1.2 mm). If necessary, add or remove adjustment shim(s). Adjust sensor until air gap between ring gear and sensor is 0.04" (1 mm).
Scheme 4
FUEL DELIVERY
Note. For fuel system pressure testing, see BASIC TESTING article.
FUEL CONTROL
- Disconnect DME control unit. Connect a jumper wire between DME relay ground terminal No. 3 (Black/White wire) and ground terminal No. 24 (Brown wire).
- Turn ignition on. Ensure fuel pump runs. If fuel pump does not run, check fuses, DME relay, Black/White wire to DME relay, Green/Black wire to fuel pump and fuel pump.
Fuel Injectors
See TESTS W/CODES article for diagnosis and testing of injector and injector circuit.
IDLE CONTROL SYSTEM
Note. Idle speed is not adjustable. For adjustment of idle switch and full throttle switch, see ADJUSTMENTS article.
IGNITION SYSTEM
Note. For ignition system checks, see BASIC TESTING article.
Fuel Tank Venting Solenoid
See TESTS W/CODES article for diagnosis and testing of fuel tank venting solenoid circuit.
System Check
Check fuel vapor lines for damage or restriction. (Scheme 5) Check connector at DME and solenoid valve for corrosion or loose fit. Check hose fitting at throttle body tight fit. Repair or replace as necessary.
Scheme 5
Poses Online