Idle Speed, Timing, and Air/Fuel Mixture
NOTE: Idle speed, ignition timing and CO are interrelated and must be checked and adjusted together.IDLE SPEED
1. Idle speed is computer controlled, and is not adjustable. If idle speed is out of specification, refer to Computers and Control Systems.
Idle RPM: Auto trans. 720 +/- 50 RPM
Manual trans: 720 +/- 50 RPM
Installing Fuse In Fuel Pump Relay:
IGNITION TIMING
Insert fuse in top of fuel pump relay (arrow), the indicator light comes on and after four seconds, ignition timing is stabilized for testing purposes.
Ignition specifications: Checking value 13-17° before TDC
Adjusting value 15 +/- 1° before TDC
The following conditions must be met before adjusting and checking the ignition timing.
1. Engine oil temperature at least 176° F. (80° C.).
2. Throttle closed, engine at idle speed.
3. Air Conditioning switched off.
Test Lead Connections For VW 1367 Or Equivalent:
4. Connect VW 1367 or equivalent engine tester according to manufacture's instructions.
NOTE: Make sure that the TDC pickup from engine tester is fully seated into the transmission housing recess.
5. Start engine and let idle. The ignition timing point is displayed directly on the VW 1367 or equivalent engine tester.
Jumper Wire Connection For Diagnostic Plugs:
6. Jumper terminal C (ground) with terminal D until ignition timing checking/adjusting is completed.
NOTE: A constant ignition timing point is available from the ignition control until 4 seconds after terminal C is jumped to terminal D.
7. Adjust ignition timing by loosening the distributor clamp bolt.
8. Rotate the distributor housing until specification is obtained.
9. Remove jumper between terminals C and D, briefly increase engine speed above 2500 RPM.
10. Let engine idle, ignition timing must fluctuate between 7° and 20° before TDC.
Ignition Timing Mark:
CHECKING IGNITION TIMING USING TIMING LIGHT
1. Connect timing light to #1 cylinder, check timing mark on flywheel.
2. Loosen distributor clamp, adjust ignition timing by turning distributor housing.
Ignition specifications: Checking value 13-17° before TDC
Adjusting value 15 +/- 1° before TDC
3. Remove fuse from fuel pump relay and increase engine speed to 2500 RPM and let snap shut. Let engine idle, ignition timing point must fluctuate between approximately 7° and 20°.
4. Tighten distributor clamp bolt.
AIR/FUEL MIXTURE (CO%)
The following conditions must be met before adjusting and checking the idle CO% content.
1. Engine oil temperature must be at a minimum 176°F. (80°C.).
2. All electrical consumers must be switched off.
3. Radiator cooling fan must not cycle during checking and adjusting.
4. Air conditioning must be switched off.
5. Fuel Injection pressure testing gauge assembly must not be connected to the injection system.
6. If fuel injection lines were loosened or replaced, raise engine to 3000 RPM's several times to clear air from lines, before any adjustments are made
7. Exhaust system must be tight and free of leakage.
8. Oxygen sensor control system must be operating correctly.
9. Ignition timing must be in specification.
Cap Removal:
ADJUSTING
1. Remove cap from charcoal canister (arrow).
Ventilation Hose Removal:
2. Remove crankcase housing ventilation hose. install plug in metal tube.
Differential Pressure Regulator Connector Removal:
3. Remove harness connector from differential pressure regulator, connect test adaptor VW 1315 A/1 or equivalent between differential pressure regulator and its harness connector.
4. Connect a high quality VOM to test adaptor and switch multimeter to 200 mA range.
CO Tap Tube:
5. Remove cap from CO tap tube and connect exhaust gas analyzer according to manufacturer's instructions.
NOTE: Hose must fit securely over the CO tap tube (arrow), so there is no exhaust leakage.
6. Start engine and let idle.
NOTE: The following procedure tests the function of the deceleration fuel shut off and the idle switch.
7. Briefly raise the engine speed to approximately 4000 RPM and snap the throttle shut.
8. The multimeter MUST indicate negative 50-60 mA for a short time. If reading indicates positive 50-60 mA, reverse meter connections.
9. If no value is indicated, check idle switch, refer to Computers and Control Systems.
Test readings should be:
VOM 0+/-3 mA
CO% 0.3 to 1.2%
10. If NO, turn off ignition, remove intake air boot from mixture control unit. Lightly center punch mixture adjusting screw plug, then drill 3/32 in. (2.5mm) hole in center of plug to a depth of 9/64 to 5/32 in. (3.5 to 4.0 mm). Using a 1/8 in. (3mm) sheet metal screw remove plug with screw , using pliers.
NOTE: Apply grease to the drill bit to catch any shavings. Clean up metal shavings from the drilling process.
11. Start engine and run at idle. Adjust CO by turning mixture adjusting screw with tool P377 or equivalent.
Specification: 0+/-1 mA.
NOTE: When adjusting do not push adjustment wrench down or accelerate engine without first removing adjusting tool. Remove tool after each adjustment and briefly accelerate engine before reading the CO value.
HIGH ALTITUDE ADJUSTMENT
1. workshops above 3280 feet (1000 meters) of elevation, disconnect oxygen sensor harness connector (green wire). Let engine idle and record mA value of differential pressure regulator current.
2. The value obtained with the oxygen sensor disconnected is the altitude correction factor.
3. Reconnect oxygen sensor harness. Record mA value and compare with the value obtained with the sensor disconnected. If the difference between readings is more than +/-3 mA.
4. Adjust CO by turning mixture adjusting screw with tool P377 or equivalent. Adjust CO% to +/-1 mA of reading taken while oxygen sensor was disconnected.
NOTE: If the reading with the oxygen sensor disconnected was 4 mA, and the reading with the oxygen sensor connected was 0 mA, the difference would be 4, making an adjustment necessary. An adjustment of 4 +/- 1 mA (with the oxygen sensor connected, would be required.