Another CIS WTF!

[ohecht]

OK, last one for tonight...

I was checking and setting my mixture using the O2 sensor test jack.

All was well and the duty cycle was right on 50%.

Moved on to double check the O2 sensor voltage just to be able to trust my settings. The voltage was fluctuating within specified limits. The Bentley manual says to let in unmetered air by loosening the oil filler cap and watch for a temporary drop in the sensor voltage.

This worked as well, but I was watching the duty cycle at the same time, expecting it to move away from 50% and then return.

Instead, it dropped to about 30% duty cycle and stayed there!!!

Dwell was also way out of spec and neither would return after I re-tightened the oil filler cap. What could cause this?

It is like the mixture setting was permanently and drastically changed just by allowing unmetered air into the system for a few seconds. I am looking for ideas from the CIS experts, please help!

Olivier

[Wayne 962]

Your mixture is probably not set properly - just go to a mechanic and have him plug it into the mixture meter. He'll probably only charge $5. Or bring it by Pelican - we have one...


-Wayne

[ohecht]

That would be great to have you guys nearby, but I am in Richmond, VA.

The last time I tried the local guys, they acted like a professional EGA was out of their reach (or broken all the time). I ended up getting the cheap EGA, but I have never trusted it since I could never get the readings to return to baseline.

What do you think of the O2 sensor test port method? Is it at all reliable if the O2 sensor is verified to be working and in good condition?

Olivier

[Superman]

I've used the dwell meter method many times on many different cars and it seemed always to work fine. On a dwell meter (not a real duty cycle meter), the fluctuating readings should center on 45 degrees. 50 would be a touch lean.

Also, O2 sensors can get loaded up wiht carbon or something, such that you need to drive the car, at temperature, to get the O2 sensor to stabilize.

[ohecht]

Jim,

I always use the duty cycle function to get 50%, and then verify that the 4-cylinder dwell is fluctuating around 45*.

I have to check it again when I get home, as this drastic change in the middle of setting it seems strange.

Olivier