Scirocco L4-1715cc 1.7L SOHC (1983)
Oxygen Sensor: Testing and Inspection
1.
Connect a dwell or duty cycle meter to the oxygen sensor test connection near the cold start valve. Connect the positive lead to the blue/white
wire, and the negative lead to ground. Set to 4 cylinder scale in dwell position.
2.
Remove fuel pump relay and connect a jumper wire with an in line switch (4480/3 or equivalent) at terminals L13 and L14 on fuse/relay panel.
3.
Turn jumper wire switch on. If ticking sound comes from frequency valve, proceed to step 10. If not, proceed to step 4.
4.
Disconnect electrical connector at frequency valve.
5.
Check contact pins and sockets of connector and frequency valve for position and damage, repairing as necessary.
6.
Connect test light across terminals of frequency valve connector.
7.
If test light does not illuminate, check wiring of frequency valve for breaks and check voltage supply of oxygen sensor relay and control unit.
8.
If wiring and voltage supply are satisfactory, replace control unit.
9.
Connect ohmmeter across terminals of frequency valve. Resistance should be 2-3 ohms. If resistance is not correct, replace frequency valve.
10.
Disconnect thermo switch electrical connectors and connect jumper wire between connector terminals.
11.
Dwell meter should read 78-82%. If reading is not correct, check wiring and repair as necessary.
12.
Check that wiring of multi-point connector is aligned with control unit.
13.
If wiring is satisfactory, replace control unit.
14.
Disconnect jumper wire from connectors and ensure that dwell meter reads 48-52%.
15.
Connect ohmmeter across terminals of thermo switch. If ohmmeter does not read infinite ohms with thermo switch temperature above 25°C (77°F)
and zero ohms with thermo switch temperature below 20°C (68°F), replace thermo switch.
16.
Disconnect electrical connectors at oxygen sensor and ground green wire.
17.
If dwell meter does not read above 87%, check wiring and repair as necessary.
18.
If wiring is satisfactory, replace control unit.
19.
Connect green wire of oxygen sensor to positive terminal of 1.5 volt "D" battery and ground negative terminal of battery.
20.
If dwell meter does not read less than 20%, replace control unit.
21.
Connect electrical connectors at oxygen sensor.
22.
Disconnect crankcase breather hose(s) at valve cover and vent to atmosphere.
23.
Disconnect charcoal canister hose at front left of bumper, then run engine at idle.
24.
After vehicle reaches operating temperature, check dwell reading at idle speed.
25.
If reading does not fluctuate, check reading at approximately 3000 RPM.
26.
If reading fluctuates, adjust idle and CO level to specifications.
27.
If dwell meter reads a constant 48-52%, replace oxygen sensor.
28.
If there is no dwell reading, replace control unit.
29.
Connect electrical connectors at thermo switch, the charcoal canister hose, and crankcase breather hose(s), remove jumper wire and install fuel
pump relay in fuse/relay panel.
