Scirocco L4-1715cc 1.7L SOHC (1983)
Air/Fuel Mixture: Adjustments
Idle Mixture Adjustment Procedures
Before adjusting fuel mixture:
a. Ensure that there are no leaks in exhaust system.
b. Connect duty cycle meter, (VW 1367 or equivalent) to engine.
c. Remove cap from exhaust manifold sampling tube.
d. Connect CO tester to tube, ensuring that hose fits snugly to prevent exhaust leaks.
e. Disconnect crankcase breather hose at cylinder head cover and leave open.
f.
Remove charcoal canister hose from the intake bellows. Leave open to atmosphere.
g. Turn off all electrical accessories.
h. Start and run engine until it reaches operating temperature and radiator fan comes on at least once.
i.
Ignition timing should be:
Automatic Trans 3° +/- 2° ATDC (vacuum hoses connected).
Manual Trans 6° +/- 1° BTDC (vacuum hoses connected).
Adjust as necessary.
j.
Idle speed should be 850 - 1000 rpm. Adjust as necessary. Shut engine Off.
If fuel lines were disconnected or replaced, run engine speed to 3000 RPM several times and let idle for at least two minutes.
Exhaust Analyzer Method
1.
Connect an exhaust gas analyzer to the sampling port pipe with the necessary adapters.
2.
With the engine running, and at normal operating temperature, disconnect the oxygen sensor plug , and observe CO reading.
3.
Reconnect the oxygen sensor and observe the reading again.
4.
The CO reading should be between 0.3 - 1.2%, and be the same with the oxygen sensor connected and disconnected.
5.
If the readings are not within specification, adjust as follows:
a. Remove the plug from the mixture control unit (between the fuel distributor and the air flow sensor funnel).
b. Insert a long 3mm Allen wrench through the hole and adjust mixture screw until the CO readings are correct.
NOTE: Accelerate the engine briefly after each adjustment.
Duty Cycle Method.
1.
Warm engine to normal operating temperature and adjust timing, and idle speed.
2.
Connect dwell meter (or suitable duty cycle meter) to the two terminal test connector (tie wrapped to the wiring harness at the cold start valve).
3.
With engine running and oxygen sensor connected, duty cycle should be 45° +/- 6° (50% +/- 6%)
4.
Remove the plug from the mixture control unit (between the fuel distributor and the air flow sensor funnel).
5.
Insert a long 3mm Allen wrench through the hole and adjust mixture screw until duty cycle reading is within specification.
6.
Remove test equipment and plug the adjustment opening.
NOTE: Accelerate the engine briefly after each adjustment.
WARNING:
When adjusting CO, do not put any downward pressure on the allen wrench. This will push the sensor plate down causing a lean condition and
kill the engine.
Do not rev engine with adjustment wrench in place. This will jam the wrench against the access hole and damage either the wrench or the sensor
arm.
