[urq] Friday the 13th - I mean Failed Emissions part2

Buchholz, Steven Steven.Buchholz at kla-tencor.com
Fri Aug 13 20:40:32 EDT 2004

300% duty cycle makes no sense whatsoever ... duty cycle should range from
0% to 100% ... is this a dwell angle reading?  If so, 300 degrees would be
83.3% of 360 degrees ... and 70 degrees would be 19.4%.  Could it have been
frequency?  I doubt that.  What is the manufacturer and model of your meter?

My stand by for verifying the dwell meter ... on the WX (sorry, I forget if
this car has an MC conversion) ... is to manually trip the WOT switch on the
throttle body when the car is at idle ... i.e. make sure both the idle and
WOT switches are both closed.  This sets a diagnostic mode in the ECU where
it forces the duty cycle to 50%.  

I'll think a bit on your data ... I know you say the motor was fairly
recently redone, but it may be that you'll be needing to check all the spark
plugs for even coloring on the insulators.  Another shotgun you can do is to
change plugs, rotor, cap and OXS ... and see what that gets you.  I usually
do this as a tune up prior to the test.  You might also be able to push
things in your favor by adding some oxygenate (octane boost) to the fuel
tank ... 

Good luck!
Steve B
San Jose, CA (USA)
> Ok, I did a little tweaking on the car and took it for a 
> re-test.  I  tuned 
> it by ear to where it sounded happiest.  (which was maybe a 
> quarter  turn anyway)  BTW, the car runs great.
> Failed again, this time the HC were about the same, and the 
> CO shot to the moon.
> Bought a multitester with frequency function and got her up 
> to operating temp.
> The settings seemed to be opposite to what the Bently said, 
> clockwise -  
> lower duty cycle, counterclockwise - higher duty cycle. 
> (switched the leads to  be sure)
> The best I could achieve was 70%, this was going 
> counterclockwise until the  
> car would nearly stall.  If I went clockwise to where the car 
> sounded good  
> (and where I started) it was in the 300% range.

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