CIS problem. Was: CIS help?

[Konstantine Bogach]

Dan,
Thank you very much for such detailed response.  I think that I have cylinders misfiring.  You cleared the doubt about oxygen sensor.  Now I am facing dead end as I don't know how to test misfiring condition.  Spark plugs are wet and I smell gas.  Are there any other, more solid approaches?  I drove to a mechanic and used his
spark power tester.  It shows min,max and spot(at current moment) voltage. What I see is 4 min-10 max KV on each wire and spot voltage is often shows as ??, then a number in the given range, then ?? again.  Mechanic only knows that it is not good but not what exactly not good. I guess it might be either low voltage or misses.
Wires are 2 days old. Spark plugs are of correct type and 2 weeks old. Coil resistances in spec.
Can I somehow confirm misfire by measurements, armed with DMM and 2 channel oscillograph?
I will try to hook up RPM and reference sensors to 2 channels of oscillograph and see if all pulses are present from rpm sensor.
I will hook up oscillograph to Hall sensor and see if it produces pulses regulary.
I don't know what else I can do.  I see 3 possible causes of the wet spark plugs: 1) weak spark; 2) some sparks miss; 3) bad atomization of the fuel (injectors).  Am I correct on it?

Thank you.
Konstantin.
2 200tq '89 - drive fine but failed CO test.

P.S. I did not want to hijack the thread so I went back to my own thread which I started earlier.

Dan Cordon wrote:

> > Having problem with CIS I followd Orin's advise and tried to adjust air/fuel mixture so the measured OXS output voltage, while it is disconnected from ECU, is ~0.5V.  I could not do it.  Voltage jumping all over the place. I can get to the point - makig it richer - where voltage stay stable at ~.87V.  Slowly making it  leaner
> > gradualy(but very small change in the screw position) reaches ~.75V and then goes to the state where voltage randomly jumps betwee 0.004V to .9V.  Going far to lean makes voltage stay at ~.001V.
> >
> > Does OXS voltage should stay more less at same level in whole voltage range while signal wire is disconnected from ECU?
> > I think it should. Then I can think of 2 possible problems: 1) bad sensor; 2) bad/intermittent combustion causing big variation of O2 content in the exhaust.  Making not very educated guess, the latter might be caused by bad spark or not good fuel mixture atomization.
> >
> > Any advise of comments are appreciated as always.
>
> Actually, what you're seeing is just fine. Depending on what type of
> meter you're using, at stoichiometric conditions you'll see either a
> jumping voltage (like you did), or a steady middle voltage. The voltage
> response of a typical O2 sensor is highly non-linear.
>
> The point where you had the voltage jumping above and below is really
> where you should set your mixture to. What's happening is that even for
> a single cylinder passing exhaust gas by, there's righer and leaner
> spots in it. If you were to use a really slow responding volt meter,
> you'd probably see something in the 0.5 volt range.
>
> It's possible that one cylinder is mis firing, but I've seen these
> fluctuations on perfectly running engines too. Most O2 circuits have
> signal conditioning to damp out the peaks you're seeing.
>
> On a whole separate note, if you have a cylinder that's frequently not
> firing, this will really throw the O2 readings off. It will register as
> a false lean condition, when in reality, it's probably rich. Just
> something to watch out for....
>
> Hope that helps some. Good luck with the tuning.
>
> --
> Dan Cordon
> Mechanical Engineer
> University of Idaho - Engine Research Facility