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Engine Controls - System/component Tests Porsche 911 Carrera 993

Testing & Diagnostics 4 illustrations ~1004 words

INTRODUCTION

Before testing separate components or systems, perform procedures in BASIC TESTING article. Since many computer-controlled and monitored components set a trouble code if they malfunction, also perform procedures 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

  1. 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.
  2. 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.
  3. 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.
  4. Avoid voltage flashover from ignition coil secondary terminal to ignition coil primary terminals (No. 1 and 15), or DME control unit may be damaged.
  5. 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).
  6. Always turn ignition off or disconnect battery before disconnecting ignition or DME control unit connectors. Electrostatic discharge may damage DME control unit.
  7. 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).

Diagnostic Circuit

  1. Locate 19-pin diagnostic connector underneath cover in front passenger footwell. Use Digital Volt-Ohmmeter (DVOM) to check wiring harness continuity between pin No. 7 (Orange/Blue wire) of 19-pin diagnostic connector and terminal No. 13 (Orange/Blue wire) of DME control unit.
  2. Use DVOM to check wiring harness continuity between pin No. 8 (Orange/White wire) of 19-pin diagnostic connector and terminal No. 55 (Orange/Blue wire) of DME control unit. If continuity does not exist, check wiring harness for open circuits.

Ground Circuits

  1. Use DVOM to check continuity to ground on Digital Motor Electronics (DME) control unit ground circuits, at terminals No. 14, 19, 24 and 30 (Brown wires). Ensure resistance is zero ohms.
  2. If reading is not zero ohms, repair open ground circuit. Check DME ground wires on cylinder No. 1 intake pipe and fuel filter mount. Check ground strap between body and transmission/engine. Ensure all electrical connections are securely attached and free of corrosion.

Ignition Trigger Circuit (Simulation)

  1. Ignition trigger signal may be simulated for trouble shooting ignition. To do so, connect an oscilloscope to ignition coil high tension lead. With ignition off, disconnect DME control unit.
  2. Turn ignition on. Intermittently connect terminal No. 1 (White wire) to terminal No. 18 (Red wire) at DME control unit wiring harness connector. A high voltage spike must be displayed on oscilloscope each time terminals are jumpered.

Ignition Output Control Signal

  1. Ensure DME control unit is properly connected. Connect oscilloscope positive lead to terminal No. 5 (White wire) and negative lead to terminal No. 2 (Brown wire) of the ignition control unit. (Scheme 7)
  2. Using ignition switch, operate starter motor. Oscilloscope must show DME control unit signal. (Scheme 7) If replacing ignition control unit, apply Heat Conducting Paste (5-942-860-003) to ignition control unit base plate.

Power Supply Circuits

See TESTS W/CODES article for diagnosis and testing of DME power supply circuits.

Scheme 7

Scheme 7: Power Supply Circuits
Scheme 7: Power Supply Circuits

ENGINE SENSORS & SWITCHES

Note. For engine sensor and switch circuits not listed, see the TESTS W/CODES article for diagnosis and testing procedures.

Scheme 8

Scheme 8: Engine Speed Sensor
Scheme 8: Engine Speed Sensor
  1. This sensor can only be tested using an oscilloscope. To do so, set-up and adjust oscilloscope using manufacturer instructions.
  2. 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.
  3. Oscillations of at least 3 volts and an intermediate higher amplitude (reference mark) signal must display. (Scheme 8) If necessary, connect oscilloscope leads to terminal No. 1 (White wire) and terminal No. 2 (Brown wire) at sensor.
  4. 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).
  5. 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 9)
  6. 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 9

Scheme 9
Scheme 9

FUEL DELIVERY

Note. For fuel system pressure testing, see BASIC TESTING article.

DME Relay

  1. 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).
  2. 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 the 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 the 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 10) 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 10

Scheme 10: System Check
Scheme 10: System Check

Poses Online

More articles — Engine Performance