cis multimeter voltage

[Ramathorn]

Okay yesterday i started my 83 for the first time in about a week and the idle was very lopy (as if it was cammed) and i diddnt have time to adjust the air/ fuel mixture so i shut her down and just took the wrx to work. Then when i got home i fiddled with it a bit and got it smooth out quite a bit and solid idle at 950 rpm's. When i hooked my multimeter up to the o2 sensor and grounded it to the multiple different spots in the engine bay my readings were waaaaay higher then the .7 volts that is ideal for the a/f mixture (mine were actually 1.89 volts). When my multimeter read 1.89 i attempted to adjust it down but, the engine started running really rough and got to the point where it was visibly shaking so i would adjust it back up.

Can someone tell me what the i am doing incorrectly?

[Bob Kontak]

Voltage should be around 0.045 volts. 0.7 volts is "too" rich if you are looking for optimum a/f ratio. 1.89 volts is very, very wrong. I don't think our O2 sensors can deliver that kind of voltage. I believe 0.9 volts is max.

Not at all trying to be a jerk, but is the multi-meter set on DC voltage? Again, just saying not implying. I don't know all of what those things can do and I always test it on a triple A battery to be sure I am in the DC volt mode.

What I would do is disconnect the O2 sensor from the wiring harness lead and test the voltage again. If it is still over 1 volt I would drop the $19 and buy a new the Bosch universal O2 sensor and check again.

Also, for grins, spend the $12 on a new O2 sensor relay from PP. Mine (81SC) was not broken but it smoothed out the running of my car. Under the pass seat attached to the CIS brain box.

How to Do a Voltage Test on a Oxygen Sensor | eHow.com

[arbita1]

Yes, something is definitely weird there. Stoichiometric mixture is .45 VDC as Bob stated. So .7 VDC would be more on the rich side. The O2 sensor doesn't put out more than .9 VDC according to Bentley.

Is the battery good in your multimeter? Try it again and see if you get the same readings.

[wrxtremest]

Originally Posted by Ramathorn

Okay yesterday i started my 83 for the first time in about a week and the idle was very lopy (as if it was cammed) and i diddnt have time to adjust the air/ fuel mixture so i shut her down and just took the wrx to work. Then when i got home i fiddled with it a bit and got it smooth out quite a bit and solid idle at 950 rpm's. When i hooked my multimeter up to the o2 sensor and grounded it to the multiple different spots in the engine bay my readings were waaaaay higher then the .7 volts that is ideal for the a/f mixture (mine were actually 1.89 volts). When my multimeter read 1.89 i attempted to adjust it down but, the engine started running really rough and got to the point where it was visibly shaking so i would adjust it back up.

Can someone tell me what the i am doing incorrectly?

#1 you need to make sure the engine is fully warm (180F or higher) before you mess with the mixture.

#2 There are a bunch of other things that could potentially be wrong to cause your symptoms. ie. Vaccum leak, fuel pressures off, AAR not functioning properly

#3 I wouldn't mess with trying to read a voltage off the O2 sensor, at least I've never had consistant luck with it.


You have an 83, so your car comes with a smart K-jetronic system. If you hook an analog dwell meter to the green wire on the Frequency Valve test port, it will tell you if you are running rich or lean. Again do this with the engine fully warm.
Most guys will tell you the next thing to do is check your fuel pressures (system pressure, cold control, warm ). This is the proper thing to do, but I dont have CIS gauges and figured out an altenative method.

The first thing I did was make my warm up regulator (WUR) adjustable. There are many threads on how to do this, just do a quick search
Next, with the engine fully warm, I set the mixture using the Dwell meter and test port.
With engine fully cold, start it and let it idle for about 30sec and then drive it. During those 30sec you are watching the idle. Does it start to bounce up and down by about 500-1000RPM and/or try to die ---> if yes, then it's rich and you will raise the plug on the WUR until the idle evens out. If it just starts and dies and/or backfires through the airbox then it's lean, and you will knock the plug in on the WUR about 1mm.
After watching for the first 30 (or so) sec then drive it. If your 30 sec idle didn't tell you much then the drive will. Does it pop and sputter on decel in gear or backfire through the airbox as you give it gas on take off---> then it's slightly lean and you need to knock the WUR plug down (just a couple of good taps). If it feels like it lugs from take off and then kicks you in the pants, or backfires through the exhaust then you are rich ---pull the WUR plug up by a quater turn (this will make sense when you see how to make it adjustable.

I found that it took a couple of days to get it perfect. I would just give myself 5 extra minutes before work and then another try before I left for home that day. Right now it runs perfectly and I didn't have to justify yet another tool purchase to my wife. =)

PM me if you have any other questions

[Bob Kontak]

Don't be dissin' the O2 sensor test. O2 sensor voltage test only requires a wire "jammed" into the O2-to-wiring harness connector to get a reading. I have had good luck with it - consistently.

I would recommend both tests. The dwell test will show how the O2 system reacts to the O2 voltage.

Once you get the O2 voltage squared away, #2 on WRXtremest's list is worthy of note. Put the fuel pressure test last and vacuum leak test first on your to-do list. Check for really basic screw ups like a fuel line not seated in an intake runner or the like.