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924martinirossi · Posted: Sat Dec 21, 2002 4:08 am Post subject: Frequency Valve

I used a DVM hat measures frequency in Hertz to check the input to the frequency valve. Upon starting the car the frequency was 68Hz with the oxygen sensor disconnected. After the car warmed up (mid mark) the reading wandered from 45Hz to 52Hz. Not sure whats going on here because without the ox sensor the system should be in open loop mode.

At 2,000 rpm's the reading went to 68Hz.

Anyways and other measurements you all have or testing/setting procedures used in regards to the ox sensor, frequency valve, air/fuel mixture settings would be great.

Thanks; Michael

John Brown · Joined: 07 Nov 2002 Posts: 903 Location: Leesburg VA

You're part way there. I recall that it is supposed to run at about 70 hz. This would tend to indicate that it is working.

Just because the O2 sensor is disconnected the rest of the system may still affect the duty cycle. The details vary with year. But there is a temp and rpm and throttle position input to most years.

But what you need to see is the duty cycle. For this the easiest and best instrument is an old fashioned dwell meter. Dan the Diesel man can chime in here, think on the 4 cylinder mode you can just about read dwell as directly as duty cycle (if it says 50 degree dwell just read that as 50% duty cycle - close enough).

Also, your frequency meter seems spot on, but as you are measuring a square wave, frequency readings can be flaky.