Modifying O2 output

[Robert Gallant]

> voltage divider wont work.  I know you said not to ask, but what are you 
> trying to do?  I've thought about what you mention, and I'm not sure you 

Thanks for all the replies about the O2 sensor.  I think I'll try just a voltage
divider with a total resistance of about 1Mohm.  If that doesn't work correctly,
I'll go with the op-amp or just run without the sensor (temporarily).

I have the new Holley ProJection Di system on a supercharged '86 Mazda Rx7.

The new Holley system is digital, comes with all sensors, and programmed with a 
laptop pc.  The old Holley system was analog.  The throttlebody is a 4bbl setup 
with four 65 lb/hr injectors and IAC.  They have throttle body's from 600-1000 
cfm and 45, 65 and larger injectors.  The fuel pump is also different from the 
old system and is capable of delivering 400 lb/hr.

The system measures TPS, RPM, MAP, O2, intake air temp, and water temp.  The Di 
version also provides the capability to program spark advance maps (I'm not 
currently using that part of the system).

The program lets you manipulate warm up enrichment, set idle speed, rev limit, 
and decel fuel cut timing.  It has programmable maps for accel pump, injection 
volume, O2 trigger voltage, and ignition timing.

The maps are 3D, with the x axis = RPM, z axis = load (MAP) on some and throttle
position on other, and y axis = the variable parameter (example is injection 
volume).

There are also two displays for monitoring the system.  One shows the injection 
volume map.  It numerically displays load, rpm, and injection volume and also 
shows the map with a pointer indicated where the engine is operating.  The other
is a numerical display that shows the output from all of the sensors plus: O2 
sensor compensation, injection volume, injector duration, ignition advance, ....

It looks as if a fair amount of thought went into the design of the system and 
has LOTS of tunability.

Now the problem I ran into is that my car like to idle VERY rich and the 
computer only lets you set O2 trigger voltages up to 0.8v.  The computer tries 
to adjust the O2 compensation to maintain the trigger voltage.  As a result the 
car won't idle.

Holley is going to burn me a custom chip (they are being EXTREMELY helpful) and 
they are thinking about the best way to accomplish the rich idle I need.  So in 
the mean time I was going to try and fool the computer by droping the O2 sensor 
voltage.  This would let, say 0.8 volts into the computer be something like 0.9 
volts out of the sensor.  Ya, ya I know the sensors are not linear way out there
but it lets the car idle!

BTW:  I have no affiliation with Holley, blah blah blah .....

Later

Rob
gallant at oasys.dt.navy.mil