nullH20

I have been running without the O2 sensor hooked up for the last couple of months.

The plastic connector in the engine compartment had broken in two awhile back, so the CIS was recieving no signal from the sensor.

I finally got around to splicing a good used connector in. After I connected everything up & started the car I get a very noticeable rapid 'knocking' or tapping sound at idle. Sort of like a really loud valve, but not exactly. When I disconnect the plug connector the sound dies down within 20 - 30 seconds. It seems louder on the left side of the engine, and once the revs rise it is no longer apparent. I drove about a mile like this & the car drives fine, it just makes this awful noise at idle!

What is going on here? How could reconnecting the O2 sensor cause this 'mechanical' noise???

The car was running great when the sensor was last connected (passed smog easily). After the connector broke I think I adjusted the idle slightle and maybe tweaked the mixture 1/8 - 1/16 turn richer. It was also running great then (although consuming more fuel).

The wire from the harness to the plug connector is shielded. Where I spliced the new connector in, the shielding is broken. I am not sure of the purpose of the shielding it only 'protects' the wire up to the connector. The 02 sensor wire itself from the connector to the sensor is not shielded anyway... or is it? Could this possibly be the problem??

Any ideas?? Thanks.

psalt

The O2 sensor signal is used to alter the air fuel mixture by pulsing the frequency valve which is located behind the airbox. It looks like a pulsed EFI injector, you need to use a mirror to see it. My guess would be that when you hook up the O2 sensor, the control box begins pulsing the frequency valve, which is making the knocking noise. I would hook up a dwell meter to the green and white wire in the test plug and watch the duty cycle of the frequency valve. It should be a steady 65% duty cycle until the system goes closed loop, and then it should rhythmically fluctuate between 45-65%. If you want a richer open loop mixture to run more ignition advance, adjust the mixture to 30-45 %. If your readings are way off, test the sensor output and replace the sensor.

nullH20

Thanks for the reply.

I do have a new O2 sensor on hand (I believe the sensor in the CAT is about 30,000 miles old or more, and 30,000 miles is the recommended replacement interval)

Perhaps I will just go ahead & change it out.

I do not have a dwell meter, but can check the O2 output w/ a voltmeter. When replacing the O2 connector I didn't touch anything else, so it must be an 02 sensor or O2 sensor wire issue. I'm really surprised at the noise that results though!! I assume that if a bad sensor is causing this I would see rapidly fluctuating voltages from the end of the sensor wire??

What would be the result if the O2 wire were accidentally grounded to the shield wire (I'm pretty sure this is not the case but could double check)?

nullH20

OK- so I tested the o2 sensor output. After running the car 10 minutes I connected a voltmeter to the connector end from the (disconnected) sensor and touched the negative lead from the voltmeter to bare metal in the engine compartment. Got readings of 0.4 - 0.6 volts, with it showing around 0.45 most of the time. Am I testing correctly?

I think this sounds like the sensor is ok??

I reconnected the sensor & now I have no noise!!?? Everything seems to be working fine? I guess I am off to get the car smogged.... we'll see how that goes.