Mitsubishi ECU

[John T Stein]

Joel A. Robinson writes:


> I have some questions that you folks may be able to answer about 
> increasing the richness of fuel mixture in case it begins to lean out in 
> the higher boost ranges.
> 
> 	1.  How can I easily monitor the A/F ratio as I drive? I have an
> 	LED bar graph guage that taps into the O2 sensor wire but I would 
> 	like to know if this guage works for all engines regardless or if 
> 	it was designed to work with only certain O2 sensors that operate
> 	in a specific voltage range.
>
An analog monitor on the O2 sensor line does yield useful information 
but ONLY if the input impedance of the meter is very high (>~10 
Megohm).  This means you will need a FET input amplifier between your 
bar graph indicator and the sensor. 

 Also, be aware that the O2 sensors typically used are highly nonlinear with what is essentially 
a step changein output voltage  at stoichiometric ratio.  As a result, your indicator 
will oscillate about 450 millivolts.  The duty cycle of the 
indicator will reflect the time-averaged AF ratio.

> 	2.  If I find that I am indeed running lean in high boost (very 
> 	dangerous condition I understand) what are some easy ways to 
> 	trick the ECU into giving me more fuel, assuming that my injectors
> 	aren't already wide open?  In the repair manual written by Haynes,
> 	it gives the voltage ranges that come out of various sensors like
> 	the coolant temperature, altitude, and some others that I can't
> 	remember.  Can I put a variable resistor inline with these signals
> 	to trick the computer into thinking its still cold?  How well do
> 	these type of mods work?
>
These "tricks"do  work but remember that signals like coolant temp 
affect many engine operating parameters that you may 
not want to alter; e.g. idle speed.

A similar trick is to rescale the output from the MAP sensor (if it 
is a voltage rather than frequency) with a resistive network at the 
output of the sensor processor. This may be a better solution than 
your switch approach.

Remember that many ECMs continuously recalibrate themselves to baseline
 readings from some sensors; e.g. Throttle position sensor reading at 
idle,  and may circumvent to your "trickery".