I need to test my o2 sensor on my 90 crx w/1.5 dpi engine. I have a digital voltmeter but need to know what to disconnect to create a vacuum leak during the test.

 

just unplug any vaccum line, I wouldnt recommend the brake booster though cause that will be a MASSIVE leak

 

What exactly are you testing it for? just to be sure that it's putting out a signal? Cause to honestly test it you should need a osciliscope to be sure it's putting out a good sine wave. But with a DMM be sure to put in on the min/max setting so you can see your lowest reading as well as your high reading.

 

If it is the single wire O2 sensor they are very cheap to replace like under $20 so it might not be worth your time to test it.

 

I had my car smog tested and it failed for high nox. The o2 sensor looks like its never been changed. The car has 88,000 miles. I have 10 days to retest or lose 40 bucks. If the o2 sensor shows lack of oxygen it will lean out the engine and cause a nox problem. Other causes could be egr and fuel pressure.

 

change the o2, get a valve adjustment, make sure timing is right on the distributor and you should pass easily.

 

do u have an exhaust leak by chance?

 

No exhaust leaks prior to the cat as far as i can tell. The muffler is starting to crack around the seem. The car runs nicely and never runs over half on temps. Just high nox.