Ignition Timing: Adjustments
NOTE: IDLE SPEED, IGNITION TIMING and AIR/FUEL MIXTURE are interrelated they must be checked and adjusted together and at the same time. This procedure should be completed once started, DO NOT stop until ALL checks or adjustments have been made. Failure to do so may result in driveability problems.
PRETEST REQUIREMENTS
The following conditions MUST be met before checking and adjusting the engine settings.
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 be running while checking or adjusting.
4. Air conditioning must be switched OFF.
5. Fuel system pressure testing gauge must NOT be connected to system.
6. If fuel lines were loosened or replaced the engine speed must be raised to 3000 RPM's several times then left idling for at least 2 minutes before adjustments can be made, this clears air from the fuel lines,
7. Exhaust system must be tight and free of leaks.
8. Oxygen sensor connected.
9. Oxygen sensor control system must be operating correctly.
TEST PREPARATIONS
CO Tap Tube:
1. 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.
Carbon Canister Cap:
2. Remove cap from charcoal canister (arrow).
Crankcase Housing Ventilation Hose:
3. Remove crankcase ventilation hose at metal tube. Install plug in metal tube.
NOTE: Crankcase vapors must vent to atmosphere (from ventilation hose) during checking or adjusting procedure.
Harness Adapter For Checking Differential Pressure Regulator Current:
4. Remove harness connector from differential pressure regulator, connect test adaptor VW 1315 A/1 or equivalent between differential pressure regulator and its harness connector.
Checking Differential Pressure Regulator Current:
5. Connect a high quality VOM to test adaptor and switch multimeter to 200 mA range.
Flywheel Timing Mark NG Engine:
6. Connect suitable tachometer to ignition coil and timing light to #1 cylinder, check timing mark on flywheel before STARTING engine if needed.
ENGINE SETTINGS CHECKING / ADJUSTING PROCEDURE
1. START engine and run to normal operating temperature (radiator fan MUST come on at least once) then let idle.
NOTE: The following procedure tests the function of the deceleration fuel shut off and the idle switch.
2. Briefly raise the engine speed to approximately 4000 RPM and snap the throttle shut.
3. The multimeter MUST indicate NEGATIVE 50-60 mA for a short time. If reading indicates positive 50-60 mA, reverse meter connections.
4. If no value is indicated, check idle switch.
IGNITION TIMING CHECKING / ADJUSTING (USING TIMING LIGHT)
Under Dash Diagnostic Connectors:
1. Locate diagnostic test connectors at drivers side footwell
Diagnostic Connectors - Activating Self Diagnostics:
2. Jumper negative (ground) terminal of test connector A with ECU terminal of diagnostic test connector B until ignition timing checking / adjusting procedure is completed.
NOTE: Fault Indicator light on dash should come on. This indicates that 4 seconds after negative terminal of connector A is jumped to ECU terminal of connector B, ignition timing has been stabilized for testing purposes.
Flywheel Timing Mark NG Engine:
3. Check timing mark on flywheel with timing light.
IGNITION TIMING SPECIFICATIONS:
Checking 13 to 17° before TDC
Adjusting 15 +/- 1° before TDC
4. If needed adjust ignition timing by removing tamper-proof cover on distributor clamp bolt then loosening the bolt.
5. Rotate the distributor housing until adjusting specification is obtained. Tighten distributor clamp bolt to 18 ft.lb. (25 Nm).
6. Remove jumper wire between terminals C and D, briefly increase engine speed above 2500 RPM to cancel fault display.
7. Let engine idle, ignition timing must then fluctuate between 7° and 20° before TDC.
IDLE SPEED CHECKING
1. Check engine idle speed.
IDLE SPEED SPECIFICATIONS
Auto trans: 790 +/- 70 RPM
Manual trans: 790 +/- 70 RPM
NOTE: Idle speed is not adjustable, the idle speed is controlled by an Idle Stabilization System, the idle air bypass screw has also been eliminated.
2. If idle speed is out of specification, check for an engine problem such as vacuum leaks etc.
AIR/FUEL MIXTURE CHECKING / ADJUSTING
NOTE: This procedure is for workshops located between sea level and 3280 feet of elevation (0 to 1000 meters elevation). For workshops located above 3280 ft. (above 1000 meters) use HIGH ALTITUDE ADJUSTMENT procedure found below.
1. Allow engine idle to stabilize then check Differential Pressure Regulator current and exhaust CO% content, with oxygen sensor connected.
AIR/FUEL MIXTURE SPECIFICATIONS (CHECKING)
Differential pressure regulator current 0 ± 3 mA
Exhaust gas CO% content 0.3 to 1.2%
2. If NO, turn ignition OFF, 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, install screw into drilled plug then remove screw and plug using pliers. Reinstall intake air boot.
NOTE: Apply grease to the drill bit to catch any shavings. Clean metal shavings from drilling process.
3. START engine, briefly raise the engine speed to approximately 4000 RPM then let engine idle.
4. With engine at idle. Adjust air/fuel mixture by turning mixture adjusting screw with tool P377 or equivalent long 3mm hex wrench.
AIR/FUEL MIXTURE SPECIFICATION (ADJUSTING)
Differential Pressure Regulator Current 0 ± 1 mA.
NOTE: When adjusting do not push adjustment wrench down or accelerate engine without removing adjusting tool first. Remove tool after each adjustment and briefly accelerate engine before reading the regulator current value.
5. Turn ignition OFF, reinstall charcoal canister cap and crankcase ventilation hose.
6. Disconnect all test equipment.
HIGH ALTITUDE ADJUSTMENT
1. For workshops above 3280 feet (1000 meters) of elevation, disconnect oxygen sensor harness connector (green wire).
Checking Differential Pressure Regulator Current:
2. Let engine idle and record Differential Pressure Regulator mA current value.
NOTE: The mA current value obtained with the oxygen sensor disconnected is the altitude correction factor.
3. Reconnect oxygen sensor harness connector (green wire).
4. Record mA value and compare with the mA value obtained with the oxygen sensor disconnected.
5. If the difference between readings is MORE than ±3 mA adjust as follows.
6. Turn ignition OFF, 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, install screw into drilled plug then remove screw and plug using pliers. Reinstall intake air boot.
NOTE: Apply grease to the drill bit to catch any shavings. Clean metal shavings from drilling process.
7. START engine, briefly raise the engine speed to approximately 4000 RPM then let engine idle.
8. Ensure that oxygen sensor has been re-connected and that mA current is fluctuating slightly.
9. With engine at idle. Adjust air/fuel mixture by turning mixture adjusting screw with tool P377 or equivalent long 3mm hex wrench.
NOTE: When adjusting do not push adjustment wrench down or accelerate engine without removing adjusting tool first. Remove tool after each adjustment and briefly accelerate engine before reading the regulator current value.
10. Adjust Differential Pressure Regulator current to ±1 mA of reading taken while oxygen sensor was disconnected (step 2. above).
EXAMPLE:
If the mA reading with the oxygen sensor DISCONNECTED was 4 mA, and the mA reading with the oxygen sensor CONNECTED was 0 mA, the difference would be 4 mA, making an adjustment necessary.
You would then make an adjustment of 4 ± 1 mA (with the oxygen sensor CONNECTED).
If the mA reading with the oxygen sensor DISCONNECTED was 4 mA, and the mA reading with the oxygen sensor CONNECTED was 2 mA, the difference would be 2 mA, NO adjustment needed.
11. Turn ignition OFF, reinstall charcoal canister cap and crankcase ventilation hose.
12. Disconnect all test equipment.