Re: 86 coupe mixture

[Fluhr <ejfluhr@austin.ibm.com>]

>I think it is time to give up on the 86 5kcstq and focus attention on my 86
>coupe taking up garage space.  I was just wondering is it possible to adjust
>the mixture on a CIS-E with a dwell meter like you can on a CIS system.  If
>not and I use the OXS what value am I looking for .5 volts, or do I remember
>the list coming to a  consensus of .7 or so.  Can't remember


The best way to adjust the CIS-E mixture, bar none, is to measure 
the pressure actuator current (AND the ISV duty cycle AND the oxygen
sensor voltage all at the same time, if you can ;-).  With the CIS-E
system, the pressure actuator is located on the fuel distributor and
has a two-pin connector.  When you measure the current (in series with
the pressure actuator), it should fluctuate around 10mA.  If it is
down below 5mA then the mixture is too rich and you should lean it
out.  If the current is above 15mA then the mixture is too lean and
you should richen it (or, more likely, fix the vaccuum leaks).  
If the current is at 0mA (lean stop, the maximum that the ECU can
compensate for a rich mixture), or 20mA (rich stop, the maximum the
ECU can compensate for a lean mixture), then (1) something needs to
be fixed and (2) you should subsequently re-adjust the fuel mixture.

At the same time that the pressure actuator current fluctuates around
10mA, the oxygen sensor voltage should be fluctuating around 0.5v.
You can adjust the fuel mixture by monitoring only the oxygen sensor
voltage, but this is not as accurate.  The ECU has a range in which
it can operate (0mA - 20mA) to keep the mixture correct, and watching
just the oxygen sensor voltage may result in the ECU operating at
one end of this range.  In such a scenario, the system has very little
room to compensate for further changes in the air/fuel mixture.

Make sure that the engine is nice and hot when you adjust it.

Note that CIS-E III systems operate basically the same way, but the
pressure actuator current ranges from -10mA to +10mA rather than
0mA to 20mA (this is done to improve driveability if the ECU dies).

Later,
Eric
'85 CGT, '82 urq
---
Eric J. Fluhr                                Email:  ejfluhr@austin.ibm.com
High End Processor Design                    Phone:  (512) 838-7589
IBM Server Group                             Austin, TX