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
- pressure measuring equipment disconnected

NOTE: If injector lines were disconnected or replaced, then run engine speed to approx. 3,000 RPM several times and let idle for at least 2 minutes prior to checking





- connect tester VW 1367 according to manufacturers instructions

NOTE: VW 1367 TDC adapter must be inserted into transmission housing as far as possible

- connect test adapter VW 1315/A1 between differential pressure regulator and its harness connector





- switch multimeter US 1119 to 200 mA scale and connect to VW 1315/A1





- connect hose from exhaust gas analyzer (Sun 105 or PA equivalent) to CO measuring tap (arrow)





- disconnect and seal crankcase breather hose at cylinder head cover (arrows)





- remove cap from T-connector at charcoal canister hose

Checking and Adjusting Idle Speed (Duty Cycle)

NOTE: Radiator fan must not be running while checking or adjusting

- start engine, allow to idle, and observe multimeter US 1119
- specification: 430 ± 20 mA

IF NO
- correct mA reading by means of idle adjustment screw
- after checking/adjusting differential pressure regulator current, check idle speed as displayed on VW 136
^ specification: 800 ± 50 rpm (manual trans.)
720 ± 50 rpm (automatic trans.)

IF NO
- check idle speed stabilizer system and repair as necessary
- switch ignition OFF

Checking OXS-Duty Cycle (CO Value)

NOTE: Radiator fan must NOT be running while checking or adjusting





- disconnect VW 1367 test lead from terminal 1 of ignition coil, and connect it to oxygen sensor test connector (blue/white wire)
- disconnect inductive pick up from spark plug wire (no. 1 cylinder)
- remove TDC sensor from transmission housing
- depress "Dwell Angle %" button on VW 1367
- start engine and allow to idle

NOTE: Ignore the RPM display on the VW 1367 tester while performing this check

- observe oxygen sensor duty cycle
- specification : 25% to 65% fluctuating
- observe CO content on EPA 105
^ specification: 0.3 to 1.2% volume (with oxygen sensor connected)

If CO value exceeds 1.2% with OXS-duty cycle from 25 - 65%, then check for the following
- Ignition system not operating property
- Exhaust system leaking
- Fuel distributor improperly distributing fuel (check and repair any or all as necessary)

If OXS-duty cycle is less than 25% or exceeds 65%, than a CO adjustment is necessary. Proceed as follows:

Adjusting OXS-Duty Cycle (CO Value)

- 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 3 mm (1.8 in.) sheet-metal screw into drilled hole
- remove plug with screw, using pliers
- reinstall air intake duct
- raise above 2,000 RPM briefly then let engine idle





- adjust OXS-duty cycle by turning CO adjustment screw with adjustment wrench P377
^ Clockwise: lowers OXS-duty cycle
^ Counter-clockwise: raises OXS-duty cycle
- speckfied value 50 ± 8% (reading must fluctuate)

CAUTION: During adjustment, do not lift or press down on adjustment wrench. Do not accelerate engine while adjusting tool is inserted in adjustment screw. Remove adjustment tool after each adjustment then briefly accelerate the engine before reading the CO value.

- after adjusting OXS-duty cycle, check idle speed and adjust if necessary
- switch ignition OFF
- disconnect CO tester and reinstall CO tap tube cap
- disconnect ignition system tester VW 1367





- remove crankcase hose plugs and reconnect to cylinder head cover





- replace cap on T-connection of charcoal canister
- conned wire for idle stabilizer to ignition coil terminal 1
- 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 drivers, 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.