Re: 86 5kTQ breakup/tuning problems

[Eddi Jew <jew@rysa.dtc.hp.com>]

 > No idea on this. Is your FI system CIS or pulsed? (My [rapidly-growing] ex-
 > perience is with the '83 UrQ, with a MAC-02 ECU, which is CIS.)
 > 
 > Hmmm... is it a "burbling" sound, kinda stumbling, or just a "miss", as
 > in no spark/combustion? Wild guess might be running overrich under high
 > rpm/boost ("rich" is good thing, too much of good thing is bad thing).
 > If your system is CIS with a "Frequency Valve", you can monitor what the
 > computer is doing to the mixture trivially with a SunPro 7678 meter (my
 > car has a convenient two-wire test connector dangling by the coil...). If
 > it's pulsed, I have no idea what to say to ya...

My experience is with CIS-E (KE-Jetronic) on '86 5000S and '86 GTI.

Is "Frequency Valve" the idle stabilizer or the fuel distributor's 
differential pressure regulator? The stock wiring harness has the signal 
from the idle stabilizer located at the coil, so I'll guess you mean that 
one. 

If the idle stabilizer signal is still "correcting" during off-idle
conditions (3000 RPM, in this case), then is there an absolute relationship
of duty cycle vs. mixture, or a relative-type of rate change? 

The differential pressure regulator's current would seem to be one that 
might get played with if enrichment is modified (like during WOT). Might
be worth monitoring that.

 > Or stick a voltmeter on the O2 sensor and see if it just pegs at +1 or so
 > volts (running rich) or near 0 volts (running lean) [if it's bouncing a-
 > round inbetween and you can't get a reading, that means the computer is
 > properly maintaining "ideal" mixture]. Typical ECU usage is to force the
 > mixture rich under max boost/rpm.

Agreed- closed-looped measurement of O2 sensor voltage would show any
mixture abnomalities. What would be an inexpensive way to determine the 
DC offset (average mixture) of the bouncing reading? Cap and resistor?
This is one area of measurement where I would like to use those analog
meters (with the high-impedance front end, of course) so I can read the
min/max bounce myself and also see dynamic trends.

Those LED bargraph O2 sensor meters do that compensation, right?

-- Eddi