Re: K-Jectronic adjustment

[MICHAEL M AGISHIAN <MEDGE@prodigy.net>]

the duty cycle is an indication of the "correction" needed , not the
"condition" of the fuel mixture.
i.e. a duty cycle of say 70%..80% means the actual mixture is lean and
needs to be pushed rich by the increased the duty cycle.
set the c.o. by adjusting the mixture screw to an average duty cycle of
50% or 45 degrees on a four cyl. dwell meter. 

Bob Rossato wrote:
> 
> I need a little help from the fuel injection experts on this list.  Subject
> car is an '86 Scirocco 8V with the K-Lambda CIS.  I recently went for
> emissions testing and failed the NOX portion of the test.  HC and CO were
> well within the limits, however, the NOX emissions were ~2800 ppm compared
> to an allowable 1400 ppm.  OK I know that high NOX is due to the car running
> lean but the problem I'm having is in adjusting the Duty Cycle on the
> Frequency valve.
> 
> I jumpered the fuel pump with the engine off to go through the regular
> diagnostics and all the default settings seemed fine.  Cold Enrichment -
> 80%; Full Throttle enrichment - 65%; O2 sensor disconnected - 50%.  When I
> started the car and let it warm up the Duty Cycle would vary from about 25%
> to 40%.  Now, on my duty cycle meter 100% corresponds to full lean and 0% is
> full rich so I assumed the meter was reading backwards as the enrichment
> settings from Cold start and full throttle are 80% and 65% (which agree with
> the Bentley values) , and during normal running duty cycle measures 25-40%.
> So if the car is truly running lean the readings make sense.
> 
> When I tried to adjust the mixture however, it got a little weird.
> Clockwise rotation of the adjustment screw is supposed to enrich the
> mixture.  However, when I tried that the duty cycle went further towards
> lean (rich on my meter). The Bentley confirms that clockwise rotation
> enriches the mixture and by inspection that makes sense as clockwise
> rotation will raise the plunger in the fuel distributor relative to the air
> plate.
> 
> So how is it that when I activate the full throttle enrichment switch the
> duty cycle goes to 65% and when I enrich the mixture via the adjustment
> screw the duty cycle goes in the opposite direction towards 0%?  What am I
> missing?  Do I trust the meter and go counterclockwise though it would seem
> that is actually leaning the mixture  out more?
> 
> Also the Lambda system seemed to act erratically in that on occasions it
> would just slowly move over to 100% duty cycle and stay there. The frequency
> valve would obviously stop cycling at this point.  If I disconnected the O2
> sensor it would revert to the 50% default.
> 
> I have changed the thermo switch for the cold enrichment (resistance values
> were in the M-ohm range when cold compared to spec of 0.5 ohm max.) and put
> in a new O2 sensor but the readings are the same, though it hasn't gone
> towards full rich yet.  I know the thermos switch isn't the culprit as that
> just affects cold running but it needed changing anyway.  Any other sensors
> that will cause the ECU to affect mixture?
> 
> Any help would be appreciated.  I need to bring it before Nov 3rd for my
> free retest.  I may just disconnect the O2 sensor and hope that 50% duty
> cycle gets me through NOX.
> 
> TIA,
> Bob R.