Engine Controls - System/component Tests Porsche 911 Carrera 4 996

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 appropriate 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/CKP sensor for compression tests, otherwise, high voltages and insulation damage to ignition coil(s), high-voltage distributor and/or 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(s) and ECM could be damaged.
3. DO NOT connect battery leads or test light to ignition coil terminal No. 1. ECM 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 No. 15), or ECM 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 ECM connectors. Electrostatic discharge may damage ECM.
7. DO NOT disconnect battery while engine is running. Reversed battery polarity could damage ignition or ECM. DO NOT exceed a charging voltage of 16 volts (including when using a battery charger).

COMPUTERIZED ENGINE CONTROLS

Note. See appropriate TESTS W/CODES article for diagnosis and testing of computerized engine control components.

ENGINE SENSORS & SWITCHES

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

Scheme 14

Scheme 15

1. Sensor can be tested using an oscilloscope. Set-up and adjust oscilloscope using manufacturer's instructions.
2. Disconnect ECM. ECM is located under driver's seat. Connect positive lead to ECM connector terminal No. 78 (White wire) and negative lead to terminal No. 20 (Brown wire). (Scheme 14) Crank engine and observe reading.
3. Oscillations of at least 3 volts and an intermediate higher amplitude (reference mark) signal must be displayed. (Scheme 15) 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). If necessary, add or remove adjustment shim(s).
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 16)

Scheme 16

FUEL DELIVERY

Note. For fuel system pressure and volume testing, see FUEL SYSTEM in BASIC TESTING article.

FUEL CONTROL

1. Disconnect ECM. ECM is located under driver's seat. Connect a fused jumper wire between DME relay ground terminal No. 3 (Black/White wire) and ground terminal No. 24 (Brown wire). (Scheme 17)
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 appropriate TESTS W/CODES article in this section for diagnosis and testing of injector and injector circuit.

Scheme 17

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 appropriate TESTS W/CODES article in this section for diagnosis and testing of fuel tank venting solenoid circuit.

System Check

Check fuel vapor lines for damage or restriction. (Scheme 18) Check connector at ECM and solenoid valve for corrosion or loose fit. Check hose fitting at throttle body tight fit. Repair or replace as necessary.

Scheme 18

Poses Online

See also:
• BASIC TESTING
• BASIC TESTING
• ADJUSTMENTS