CIS problem. Was: CIS help?

[Dan Cordon]

No problem. Misfiring conditions are hard to test...period. The trouble comes because there can be SO many reasons for the misfire. One thing that I always start with is by pulling the plug wires one at a time (I wear a high voltage glove to keep from getting shocked). If a cylinder is firing correctly, the RPM will drop and the
engine will run noticeably rougher. By doing this I can usually tell if one or two cylinders are bad, or if it's a problem up stream (like a bad coil or signal) that effects all the cylinders equally.

>From what you describe on the spark power meter, I'm guessing that each of the cylinders is having mis-fire at some point. You may try pulling individual plug wires to confirm this though. If that's the case, the problem is more likely in either the coil, or signal to the coil. Of course, it wouldn't hurt to check the cap and rotor
too. Of nothing else, clean the contacts up.

You mentioned the plugs being wet. Are all of them getting wet, or just a few? Typically, once a plug is gas fowled, they don't recover. I've had good luck heating the plugs with something like a propane torch and immediately putting them in the car. However, this only seems to work for the duration of the car running. Once you shut
it off and let it cool down, they're likely to be troublesome again. (I learned this while tuning my drag mustang ages ago.....was eating plugs by the day. Used this trick until I finally got the carb - eck...carbs - set correctly, then swapped in a new set of plugs).

Of the three reasons you list, I'd say the last reason (poor atomization) is the least likely. Gasoline is usually volatile enough that pouring a stream of fuel down a carb allows the engine to start. I'd concentrate more on searching for intermittent sparks from something like a bad hall sensor or something. Wish I could help, but
don't have an O-scope at home. :o(

Konstantine Bogach wrote:

> 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
Mechanical Engineer - Engine Research Facility
University of Idaho