Ignition Timing: Adjustments
Idle Speed, Ignition Timing And OXS-duty Cycle (CO Value) Must Be Checked And Adjusted Together
Checking/adjusting conditions:
- engine oil temp. minimum 80°C (176°F)
- throttle valve in idle position
- throttle valve switch OK
- coolant thermo-switch OK
- all electrical consumers switched OFF
- air conditioner switched OFF
If injector lines were disconnected or replaced, then run engine speed to approx. 3000 RPM several times and let idle for at least 2 minutes prior to checking
- connect tester according to manufacturers instructions
NOTE: TDC sensor must be fully seated into transmission housing
- disconnect double connector from terminal 1 of ignition coil
- reconnect double connector so that terminal for idle stabilizer (green/white wire) is open (arrow)
- pull cap off CO tap tube and connect hose from CO tester (arrow)
NOTE: Hose must fit securely over CO tap tube so there is no exhaust leakage
- disconnect and seal crankcase breather hose from cylinder head cover (arrow)
- disconnect air intake hose from activated charcoal canister. Do not seal
NOTE: Elbow connection must remain installed in air intake duct since it has a calibrated bore
- start engine
- adjust idle speed (arrow)
- specified value: 800 ± 50 RPM (for both man. and auto. trans)
NOTE: Radiator cooling fan must not be running while testing and adjusting
- check ignition timing and adjust as necessary (vacuum hose remains connected to ignition distributor)
NOTE: Ignition timing will be displayed on tester.
- adjust as necessary
^ checking 6 ±2° BTDC
^ adjusting 6 ± 1° BTDC
- after adjusting ignition timing, check idle speed. Adjust as necessary
- switch ignition OFF
- measure OXS-duty cycle using VW 1367
- disconnect tester cable from contact 1 on ignition coil and connect to blue/white wire of Oxygen sensor
- disconnect terminals from cylinder 1 ignition cable and TDC sensor
- press Dwell Angle % button
- start engine and let idle
NOTE: Pay no attention to RPM reading displayed by tester
- check OXS-duty cycle
^ specification: 25 - 65% (reading must fluctuate)
^ CO value: 0.3 - 1.2% (Oxygen sensor connected)
NOTE: If CO value exceeds 1.2% with OXS-duty cycle from 25 - 65%, then check for the following:
- Ignition system not operating properly
- Exhaust system leaking
- Fuel distributor improperly operating
^ Check and repair any or all as necessary
If OXS-duty cycle less than 25% then adjustment is required
- switch ignition OFF
- remove air intake duct from air flow sensor
- center punch mixture adjusting screw plug
- drill 2.5 mm (3/32 in.) hole in center of plug 3.5 - 4.0 mm (9/64 - 5/32 in.) deep
CAUTION: Clean up any metal shavings. Apply grease to drill bit to catch shavings.
- screw in 3 mm (1/8 in.) sheet-metal screw
- remove plug with screw, using pliers
- reinstall air intake duct
- start engine and let idle
- adjust OXS-duty cycle by turning CO adjustment screw with wrench P377
^ Clockwise: lowers OXS-duty cycle
^ Counter-clockwise: raises OXS-duty cycle specified value: 50 ± 8% (reading must fluctuate)
CAUTION: Do not accelerate engine with tool in place. Remove tool after each adjustment and accelerate engine briefly before reading current mA. Always adjust in direction from HIGH to LOW.
- after adjusting OXS-duty cycle, check idle speed; adjust if necessary
- switch OFF ignition
- disconnect CO tester and replace CO tap tube cap
- disconnect ignition tester
- remove crankcase vent hose caps and reconnect to cylinder head cover
- reconnect hose to activated charcoal canister
- drive in new mixture adjusting screw plug
NOTE: After adjusting, the hoses for the crankcase must be reconnected. If the control current and the CO content change, this is not due to an improper adjustment, but rather to oil dilution caused by short distance driving. With long distance drives, the amount of fuel in the oil will be reduced and the CO value will normalize again. A short term solution would be an oil change.