O2 Sensor Open/Close Loop

[Mazda Ebrahimi]

RABBITT_Andrew at mv8.orbeng.com.au wrote:
> 
> >The vehicle tested is a 1997 GMC 2500 P/U with a 5700 Vortec V-8.  I
> >logged MAP, RPM, TPS (0= closed, 400= WOT), and O2 volts.  You can
> >see the sensor voltage toggles all the way through WOT points.
> 
> Interesting data there.  A couple of questions though; you say 400 =
> WOT, but the maximum value is only 396.  Is 400 the exact WOT
> breakpoint (in which case it never went into WOT mode) or is it
> something else?  If so, do you know what it is?
> 
> I noticed a lonely WOT flag at t=9.34 s, but not during the second
> tip-in.  Is this your notation or from the ECU?
> 
> I know that the EEC-4 delays open-loop operation for a few seconds
> after entering WOT mode.  Might this be the case for GM, only longer?
> 
> Andrew Rabbitt

Hi Andrew,
The system I used to log this data is a Compressed Natural Gas system 
which piggy-backs the OEM computer.  I ran the vehicle on gasoline, in 
which case the natural gas system basically monitors various sensors 
independant of the OEM.  
I mentioned 400 is the maximum value possible.  There is a calibration 
process that I perform to let the natural gas system know what WOT 
voltage is.  going to 396 instead of 400 is simply a calibration error 
on the natural gas system.  I did have my foot all the way on the pedal.

Also, I added the WOT flag later to show a sample of the data.  I guess 
I should have added a second one for the second WOT region.

Regarding the delay in enrichment for WOT, that is an interesting point 
which I will investigate tomorrow.  I won't be surprised if that is the 
case, because I have found many OEM strategies change as soon as you 
exit the limits of the FTP-75 and I/M-240 test cycles.