Help Troubleshooting O2 Sensor System
 

I've started looking into my O2 sensor system (which I believe not to be working). I have the Bentley Manual and the James Weber book - Solving Bosch CIS Problems.

So far, this is what I've done -

1. Checked duty cycle with dwell meter as follows:

- key in run position (engine not running), I grounded the 15 deg. thermal switch. This should simulate a cold engine. The duty cycle is a constant 11%. (It should be around 45%.)

- same as above, with the thermal switch not grounded. This simulates a warm engine. The duty cycle is constant at 16% (It should be around 50%.)

- Now I reconnected the thermal switch and disconnected O2 sensor and grounded the wire. This simulates a extreme lean condition. The duty cycle goes to 0% and frequency valve shuts off. (It should be 95%)

- Then I added a D-Battery to give 1.5V to the O2 sensor wire. This simulates an extreme rich condition. The duty cycle was 7%. (This was the only correct test I got, as it should be around 10%)

2. I checked the frequency valve and it appears to be functioning as it is buzzing. I can hear it and feel it.

3. Not really related, but I checked the 15 deg. throttle sensor switch. In the closed position, I did not get any continuity, so I don't believe this is working.

That's as far as I got last night. Any comments?

First, what is it you're trying to fix here?

I have doubts that the O2 sensor system is functioning properly. I'm trying to verify this prior to hooking it back up. It is currently disconnected.

OK, this will get you started. If you have/had leaks in the CIS system (air) people will often times richen up the mixture to get the car running well again. When this is done the mixture falls outside of what the O2 sensor and lambda computer can compensate for.

That being said, when people rich up the mix they unplug the O2 sensor as it will cause the lambda system to oscillate the idle and screw around with the mixture as it tries to bring things back into the operating range.

Plug the sensor back in, does it cause the idle to go out of wack? If so the sensor and system are working just fine. The fact that the car runs means the basic components of the lambda system are working. You can test this by unplugging the relay to the lambda computer and see how the car runs after that... if at all.