Emission Control Systems: Adjustments

Requirements:
- Engine oil temperature minimum 80°C (176°F)
- All electrical consumers switched OFF
- Oxygen sensor connected





- remove cap from exhaust probe
- connect hose from exhaust gas analyzer (Sun 105 or EPA equivalent) to CO measuring tap (arrow)





- remove carbon canister vent hose from elbow at intake air boot (arrow)

NOTE: Leave elbow unplugged to draw in fresh air through restrictor.





- remove crankcase breather connections at valve cover
- plug both openings at connector (arrows)

NOTE: Crankcase vapors must vent to atmosphere during checking or adjusting procedure.





- connect multimeter US 1119 or equivalent to differential pressure regulator with adaptor VW 1315 A/1
- set scale to 200mA DC





- connect engine tester to check ignition timing and idle speed
- start engine and run to normal operating temperature

NOTE: If the injector lines are loosened or replaced, the engine should be run at about 3,000 RPM for several minutes to bleed injectors and lines.





- insert fuse in top of fuel pump relay

NOTE: Indicator light must come on. This indicates that ignition timing is stabilized for testing purposes, after four seconds.

- check ignition timing
^ specification: 13° to 17° before TDC

If specification is NOT obtained
- adjust ignition timing to: 15° ± 1° before TDC
- remove fuse from fuel pump relay and briefly raise engine speed above 2,500 RPM to cancel fault display
- check idle speed
^ specification: 720 ± 70 RPM





NOTE: The idle speed is NOT adjustable. The idle air bypass screw should be turned in fully against its seat.

- if idle speed is out of this range, check for an engine problem such as vacuum leaks, etc.
- check differential pressure regulator current with oxygen sensor connected
^ specification: -1mA to +1mA

If specification is NOT obtained
^ adjust to specification
- check CO%
^ should be 0.3% to 1.2%

If NO
- Check and Adjust CO
- disconnect testers and reconnect hoses on engine

Checking and Adjusting CO
- Engine oil temperature: minimum 80°C (176°F)
- Ignition timing point OK





- remove cap from CO probe receptacle
- connect CO test hose to probe receptacle (arrow)
^ hose must fit snug so there is no exhaust leak





- disconnect and plug crankcase ventilation hoses at cylinder head cover (arrows)





- remove charcoal canister hose from intake air boot and leave open

NOTE: Intake air boot hose connector has a calibrated orifice and must remain open.

- start engine

NOTE: If injection lines were disengaged or replaced, the engine speed must be raised to 3,000 rpm several times and left idling for at least 2 minutes before adjustment. The idle speed is automatically regulated by the idle stabilization valve.

- disconnect oxygen sensor connector
- check CO-value, if necessary adjust with CO-adjustment screw
^ checking value: 0.3 - 3.0 vol. %
^ adjusting value: 0.6 - 1.0 vol. %

NOTE: If the CO value is less than 0.3 or more than 3.0% volume when the oxygen sensor is disconnected; adjust the CO as follows:

- switch ignition OFF
- remove rubber boot from mixture control unit
- center punch mixture adjusting screw plug
- drill 2.5mm (3/32 in) hole in center of plug approximately 3.5 to 4.0mm (9/64 to 5/32 in) deep

CAUTION: Clean up any metal shavings. Apply grease to drill bit to catch loose shavings.

- screw in 3mm (1/8 in) sheet metal screw
- remove plug/screw, using pliers
- reinstall rubber boot
- start engine and run at idle





- adjust CO by turning mixture adjusting screw using Tool P377
^ counter-clockwise: CO value increases
clockwise: CO value decreases

CAUTION: When adjusting do NOT push adjustment wrench down or accelerate engine with adjusting tool in place. Remove the tool after each adjustment and briefly accelerate engine before reading CO value.

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.

After adjusting, the specified value must fluctuate with the oxygen sensor connected.

If NO
- check the oxygen sensor