[urq] AF meter

[Buchholz, Steven]

The wideband unit is one thing I might recommend if you really wanted to know how the mixture was in your car, but it wouldn't help the ECU at all.  The ECU is designed to operate with the "switch" and would more likely than not get confused by the output of the wideband sensor.  The wideband systems were designed to allow the ECU to control the mixture at those max power and best economy points.

There are WBO2 products on the market from Innovate Motorsports and PLX devices.  Some provide simulated narrow band OXS outputs for compatibility.  They certainly would be a good item for the tool box if you are trying to get the most out of your engine.  The thing is that the WBO2 is still only a single point sensor, so you might run into problems when there is one cylinder which is not getting the same mixture as the rest.  My personal favorite for a feedback system on the cylinder performance on a per cylinder basis is "ION sensing" ... where the system monitors the voltage across the spark plug after the ignition pulse.  This will give information about the mixture in the cylinder as well as whether or not detonation is occurring.  AFAIK nothing off the shelf here though.  The other thing you can do is to get EGT at the exhaust from each cylinder.  The private aviation marketplace has some cool gauges for monitoring this ... kinda spendy though ... 

Steve B
San José, CA (USA
> 
> Given the narrow range of the stock 02 sensor, would it make sense to upgrade
> to a "wideband" sensor (seemingly a popular modification to contemporary cars,
> especially turbos)?
> Would the ECU be able to take advantage of the additional information or would
> it just confuse the system?  Does the ECU (perhaps specifically the fuel map)
> have enough resolution to respond to the more detailed input?
> --Ken
> 
>  -------------- Original message ----------------------
> From: "Buchholz, Steven" <Steven.Buchholz at kla-tencor.com>
> > ... the 'heart beat" is not a big surprise because that's the way the system
> > works.  You should not think of the OXS as much more than an on/off switch.
> > What the ECU does is to flip the mixture slightly back and forth across
> stoich
> > when it is operating in closed loop mode to make sure it is in the stoich
> > ballpark.
> >
> > As a reference, it is generally accepted that an engine produces the most
> power
> > at lambda = 0.9 and best fuel economy at lambda = 1.1 [Bosch Automotive
> > Handbook].  The standard "narrow band" OXS has a signal that is "off" at
> 0.975
> > lambda and fully "on" at lambda of 1.025.  This means that the best the
> "A/F"
> > meter can tell you is whether or not the mixture is above or below stoich.
> I
> > too have one of Orin's meters ... I planned to install the LED display in
> one of
> > the unused switch blanks on the dash ... but by no means should anyone spend
> a
> > lot of money on the 20 LED displays ...
> >
> > The fact that the OXS has such a narrow active range is why most older
> engines
> > are allowed to go open loop at WOT ... it also means that the ECU does not
> have
> > direct feedback to determine that the engine is running at the mixture for
> best
> > fuel economy when in closed loop too ...