Re: lambda sensor

[bearbvd@domain.elided (Greg Hermann)]

>Yes, a lambda sensor is the same thing as an O2 sensor. I know Wes Ingram
>runs his race cars with them fitted. There are several things to remember
>about O2 sensors:
>
>1) All lambda-type O2 sensors are basically the same. A one-wire sensor
>has only the sensing element. The voltage is picked up at the wire, and
>the body is the ground. A 3-wire sensor has a heater element to get it
>up to temperature faster, that's all. A 4-wire sensor has the sensing
>element isolated from the body, so a separate ground wire is needed.
>
>2) All modern EFI systems use the lambda sensor as a switch. The computer
>constantly runs the mixture from lean to rich and back again across the
>ideal point. This is like an auto-zeroing or chopper-stabilized system
>to cancel out noise. The EFI brain does not use the sensor in analog
>mode.
>
>3) Aftermarket O2 meters do use the lambda sensor in analog mode. On a
>car with EFI, this is probably a waste, because of #2 above. On a car
>with Spica or Webers, they can really help tune a car for performance.
>All the aftermarket O2 meters are based on the National Semi LM3914N.
>The design is virtually straight out of the National Semi databook. For
>the irrepressible do-it-yourself types, a schematic is available at:
>
>  ftp://ftp.team.net/misc/o2meter.pdf
>
>4) All generic O2 sensors use the same thread as an 18mm spark plug.
>That's not 14mm, like in an Alfa engine, that's 18mm, like in some big
>American lumps of pig iron. You can get a fitting to add an O2 sensor
>at any auto parts store. The thing to look for is called a spark plug
>non-fouler. Get the 18mm, gasket-base spark plug non-fouler and cut
>the threads off. Drill out the center, if needed, then weld into the
>exhaust as close as possible to the motor, but after all runners are
>combined into one pipe. V-6 and V-8 motors can run 2 sensors, and 2
>displays, or have a left-right switch for the display. ** USE ANTI-
>SIEZE ON THE O2 SENSOR THREADS. **
>
>Simon

Nice summary, Simon.

Except that I would add that a regualr lambda sensor is best only used as a
switch. It basically detects the presence or absence of oxygen in the
exhaust gas stream. Any meter that purports to use one of these sensors to
try to read the air fuel ratio outside of a range from about 13.8 to 15.5 :
1 is guilty of a LOT of wishful thinking, and is guilty of SOME wishful
thinking even within that range.

Both Bosch and NTK/NGK make so-called "WIDE BAND" O2 sensors. The NTK unit
is generally accepted as being the better of the two. The Bosch unit was
used on the Porsche 930 turbos. The NTK unit has been used on some Honda
VTEC motors. These units will measure mixture ratio from 10 : 1 on out to
30 : 1 or leaner--and do it rather accurately if properly calibrated.
BUT--they are quite a bit more pricey than the usual aftermarket
(so-called) mixture meters.

The least expensive wide band mixture meters I know of to date are still
over $1000 each.

Regards, Greg

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