Re: exhaust monitor

[jlandry@domain.elided (John A. Landry)]

The black helicopters hovering over the house recorded Terry Rust
<trust@domain.elided> whispering:

>A while back one of our most exhaulted gurus developed an exhaust monitor
>for use while driving down the road and tuning ones projection. In my
>ignorance I did not treat that information with due respect (I seem to have
>trashed it). Could we get that posted to the FAQ or someplace where I can
>refer back to it, several of us would like to give it a try and I can't
>remember the details.
>
>Thanks, I promise I won't trash it again.

Terry,

I'm not one of the "guru's", but I've used an air / fuel monitor in two of
my cars now and can share a few tid bits of advice with you...

I bought the air / fuel ratio gauge manufactured by Cyberdyne.  This is a
modern multi-colored bar graph type gauge.  It's sold through the standard
channels like Summit Racing and Jegs (both on the web).  I don't have the
catalog in front of me, but I recall the cost being under $40.00.

You'll need an oxygen sensor to actually sample the exhaust and provide the
signal for the gauge.  Go to any chain auto parts store and buy the
cheapest "one-wire" oxygen sensor they have.  I happened to buy a Bosch
sensor for about $25.00 I think.

You'll need to drill a hole in your exhaust system as close as possible to
one of the exhaust manifolds as possible.  This heats the sensor quickly
and keeps it hot enough to function accurately.  Many folks install the
sensor in the collector if they have headers.  This is fine but means the
sensor may not provide accurate readings at idle.  In that position, the
engine rpm has to be increased before the sensor is heated enough to give
accurate readings... usually when driving.

If you do have to install the sensor away from the exhaust manifold (like
in a header collector), then you can spend a little more on a heated oxygen
sensor.  This would be called a "three wire" sensor.  One wire is the
output signal and the other two are wires that connect to an internal
sensor heater.  This type of sensor provides enough heat on it's own to
give proper output no matter where it's installed.

Going from memory... to install the sensor, you will need a 10mm x 1.5
pitch nut.  Just so you can verify my feeble memory, the threads on the
oxygen sensor are the same size and pitch thread as the spark plugs on the
engine.  You can buy the sensor first and take it with you when you go to
buy the nut.  This size nut is slightly rare, so you may have to get them
from a really good hardware store or an industrial fastener store.  To
install, you basically drill a hole in the exhaust pipe, braze or weld the
nut in place, and install the sensor.  Hook up the wires per the
instructions with the gauge and your in business.

On my Traveler, I installed the sensor on the top of the right exhaust down
pipe, just to the rear of the starter.  This turned out to be acceptable in
terms of sensor function, although the sensor is not heated enough to give
really accurate readings during idle.  It's also a place that offers a
decent amount of clearance for the sensor.  On the other hand it turned out
to be a bad location because my rear main seal leaks.  Oil drops find their
way onto the exhaust pipe and the sensor.  The oil fumes cause the sensor
to give false mixture readings because the sensor works by "sampling" the
outside air (around the sensor body) as well as the exhaust gases.  The
difference in these two gases is what causes the output signal of the
sensor.  Burning oil fumes tricks the sensor and causes a false output.

So, if you have a leaky rear main, the sensor really needs to be someplace
else.  When I get the time and desire, I'm going to move my sensor up
higher, closer to the exhaust manifold.  I found installing the sensor was
easiest done by sawing out a section of the old down pipe, taking it to an
exhaust shop and having them make a new one slight longer to slip over the
old remaining exhaust pipe.  That way you have the piece off to drill and
braze or have the exhaust shop do it.

Good luck,

John
------------------------------------------------------------------------
jlandry@domain.elided             |
Conservative Libertarian        |  Scout(R) the America others pass by
Life Member of the NRA          | in the Scout Traveler escape-machine.
WA Arms Collectors              |
Commercial Helicopter - Inst.   | 1976 Scout II Traveler "Patriot" model
http://www.halcyon.com/jlandry/ |     1977 Scout II Traveler (Parts)