CO Content

Fig. 7 Differential Pressure Regulator Test Setup:

1. Initial Setup
a. Engine at full operating temperature, 80°C (176°F)
b. All electrical consumers turned OFF, (A/C and radiator fan should not come on while testing).
c. Fuel pressure gauges must not be connected to the system
d. Exhaust system must be in good condition.
e. If any fuel injection parts have been replaced, or the system has been opened for any reason, run the engine at around 3000 rpm for two minutes, to bleed any air from the system, before testing.
f. Remove charcoal canister hose and connector from intake air boot , and leave vented to atmosphere. The connector is a calibrated orifice and should remain connected to the hose while testing.
2. Connect test harness (VW 1315A/1), Fig. 7, to the differential pressure regulator.
3. Connect a multi-meter to the test harness, on the 200 mA scale.
4. Remove the cap from the exhaust manifold sampling pipe, and using the necessary adapters connect a suitable CO meter.

Fig. 13 Duty Cycle Test Connector:

5. Connect a digital dwell or duty cycle meter (VW 1367 or equivalent) to the two terminal oxygen sensor test plug, (located near the fuel supply line by the right front strut tower) Fig. 13.
6. With engine at idle, and the oxygen sensor connected, the duty cycle should be 28mA +/- 2%.
7. If the duty cycle is not within specification, disconnect the oxygen sensor and adjust the air bypass screw on the throttle housing until the duty cycle is 28mA +/- 1%.
8. Idle speed should be 750 - 850 rpm. If Idle speed is not within specification, see "IDLE CONTROL VALVE."
9. With oxygen sensor disconnected, CO should be 0.3 - 1.2% at idle.
10. If CO is not within specification;
a. Turn ignition OFF
b. Remove air boot from air flow meter.
c. Drill a 2.5 mm (3/32 in) hole in the anti-tamper plug, then screw in a sheet metal screw. Use pliers to remove plug.
d. Re-install air boot, and start engine.
e. Adjust the CO by turning mixture screw with a 3mm allen wrench (tool P377 or equivalent).
f. Remove tool after each adjustment, and briefly rev the engine before reading CO value.
g. Adjust CO to 0.6 - 1.0%.
CAUTION:
1. When adjusting CO, do not push down on the adjustment wrench, as this will cause the engine to run lean and die, or backfire and damage the air flow sensor.
2. Do not accelerate the engine with the adjusting tool in place as this will cause the tool to bind in the adjusting hole, possibly damaging the took, the air flow sensor, or both.
11. If the CO value is OK, observe the differential pressure regulator current reading with the engine at idle, and oxygen sensor disconnected. Reading should be as shown in Fig. 4.
a. If current values are not within specification, check altitude sensor.
b. If current values are OK, reconnect oxygen sensor and recheck the duty cycle.
12. Duty cycle should be 28 +/- 2% and current should fluctuate slightly.
a. If current does not fluctuate, check oxygen sensor.
b. If current fluctuates, system is working normally. Shut engine off, disconnect test equipment, and reconnect all hoses.