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Re: K-Jectronic adjustment

> 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.

with a working OXS in the circuit the only way the car can run lean is
if the freq valve can no longer make the engine any richer.

I don't know about your meter but duty cycle is duty cycle - 25% to 40%
is a bit "low".  The car is running fine but technically the DC range is
supposed to be around 50%.  many people set it lower though to make the
relative extra richness of WOT even more so.  awful sentence, sorry.

> 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).

please use numbers.  I'll ignore your weird meter for now.  When you
adjust the mixture the car *does not get leaner or richer*, the CIS
keeps is as close to stoich as it can until it runs out of range.

Waht you are saying is that as you adjusted it, the duty cycle changed -
turning the screw CW (more fuel) should result in a lower DC %.  which
is not the way you need to go.

> 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?  

The CIS cannot be adjusted "rich" or "lean".  It is designed to
compensate and always run right at the optimum (or oscillate around it)
within its limits of control.

> 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. 

since 100% duty cycle = "always on", it would stop clicking I suppose...

> 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. 

Well, new OXS saves me wondering about that... but please, again, use
numbers for your measurements - what are you calling "full rich"?

> 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.

I would at least check the ground wire at the intake manifold.  That is
the ground for the ecu - if it is bad everything else will be a little
off.  Whoa, it is on Audis anyway!  I imagine the rocco would be
similar.  Also take a look, at and clean, general tune up items just to
be on the safe side.  Is your timing set at stock?  Run gas tank low,
get some good premium, execute "Italian tune up" (drive around block, or
whatever, at high rpms...!), this is just general de-cobwebbing.

Also - when were you injector seals last replaced?  New they are nice
soft rubber, old they are hard nasty little donuts.

anyway, if you want to go into this further you can also email me
privately to spare the rest of the list the agony if you want.  I did
this reply in public to generate corrections in case I am way off base

Huw Powell


82 Audi Coupe; 84 4kq; 85 Coupe GT; 73 F250