Engine Controls - Adjustments Porsche 911 Carrera 964

INTRODUCTION

Note. Introduction information not applicable.

ENGINE MECHANICAL

Before performing any on-vehicle adjustments to fuel or ignition systems, ensure engine mechanical condition is okay.

VALVE CLEARANCE

Adjust valve clearance with engine cold. Refer to the VALVE CLEARANCE SPECIFICATIONS . Adjust valves in firing sequence: 1-6-2-4-3-5. Marks for TDC of each cylinder are located 120 degrees apart on crankshaft pulley.

VALVE CLEARANCE SPECIFICATIONS

IGNITION TIMING

Ignition timing is controlled by DME engine management system and is not adjustable. Value given in the IGNITION TIMING is for verification purpose only.

IGNITION TIMING

Scheme 1

CRANKSHAFT POSITION/SPEED SENSOR

Note. Clearance between crankshaft position sensor and gear ring must 0.03" (0.8mm). The reference mark sensor will also be positioned correctly, if this value is adjusted correctly.

With Engine Removed

Screw in crankshaft position sensor tight in holder. Loosen mounting screws on holder. Adjust clearance between gear ring and crankshaft position sensor to 0.03" (0.8mm) with a feeler gauge blade.

With Engine Installed

1. Remove speed sensor. If available, a faulty sensor can be used as an adjusting tool. Then glue a 0.03" (0.8mm) thick washer on sensor with a quick-drying glue as a clearance gauge. The sensor installed in car could also be used if procedures are carried out carefully. Then the glued surface must be kept as small as possible or an easy-to-remove glue must be used.
2. Loosen screws on holder and screw in finger tight so that holder can still be moved on its pivot point (bottom screw). Install extended sensor in speed sensor opening and tighten.
3. Move holder with extended sensor against stop (gear ring) and then tighten holder screws. Remove extended sensor. If original sensor had been used, press off washer carefully and remove glue. Install speed sensor and tighten to 6 ft. lbs. (8 N.m).

COLD (FAST) IDLE

Fast idle speed is controlled by DME engine management system and is not adjustable.

IDLE MIXTURE

Note. Mixture adjustment is NOT part of normal tune-up procedure and should NOT be performed unless fuel injection components and/or control units are replaced, or vehicle fails emission testing.

1. Connect exhaust gas test line to test point in front of catalytic converter. By-pass idle stabilization system. Connect CO tester and tachometer. When engine is at operating temperature, turn regulating screw or by-pass screw on throttle until proper base idle speed is obtained.
2. Pull off rubber cap and disconnect plug for oxygen sensor at left side of engine compartment. If CO level is not correct, adjust mixture screw. Screw is located on airflow meter.
3. Always adjust mixture from lean to rich using Adjusting Wrench (P 377). Reconnect plug for oxygen sensor. Coat threads of test connection with molybdenum paste and install.

IDLE SPEED & CO LEVEL

IDLE SPEED

Only base idle speed can be adjusted. The Digital Motor Electronic (DME) engine management system processes idle speed switch position, engine temperature and engine speed, then signals idle speed positioner to change idle speed as necessary. If idle speed control fails, control diaphragm is moved to a given clearance against the stop, allowing minimum operation.

IDLE SPEED SWITCH (M/T)

1. Disconnect throttle position sensor. Using an ohmmeter, check continuity between idle switch terminals No. 1 and No. 2. (Scheme 2) With throttle valve closed, ohmmeter reading should be less than 10 ohms.
2. Open throttle valve beyond one-degree angle. With throttle valve open, ohmmeter reading should be infinity. If ohmmeter readings are not as specified, adjust idle switch.
3. To adjust switch, use a 0.036" (0.9 mm) feeler gauge to adjust clearance between idle speed switch housing and drag lever when throttle valve is closed. (Scheme 3)

Scheme 2

FULL THROTTLE SWITCH (M/T)

1. Disconnect throttle position sensor. Using an ohmmeter, check continuity between full throttle position switch terminals No. 2 and No. 3. (Scheme 2) With throttle valve closed, ohmmeter reading should be infinity.
2. Open throttle valve at least 2/3 of the way. With throttle valve open, resistance should be less than 10 ohms. If ohmmeter readings are not as specified, adjust full throttle switch.
3. The full throttle switch must be adjusted so the switch contacts will close at throttle angle of about 70 degrees. (Scheme 3)

Locating Idle Speed Switch & Full Throttle Switch. Scheme 3

THROTTLE SWITCHES RESISTANCE SPECIFICATIONS

THROTTLE VALVE POTENTIOMETER (A/T)

Automatic transmission (Tiptronic) vehicles have a throttle valve potentiometer instead of a full throttle switch on throttle valve housing. The potentiometer is used exclusively for transmission control. In addition to the potentiometer, a full throttle switch for DME control unit, and an adjustment switch for throttle valve potentiometer are also located on throttle valve housing. Adjust throttle valve potentiometer so that a click is heard when the small diameter throttle valve plate begins to open.

Note. DO NOT confuse the throttle valve potentiometer adjustment click with the click produced by idle speed switch contacts.

Poses Online

See also:
• VALVE CLEARANCE SPECIFICATIONS