Re: Lambda Testing by SM

["Scott Mo." <scottmo@teleport.com>]

QSHIPQ@aol.com wrote:

> Couple of issues on the numbers.  Nice report btw Scott.
>  A high CO value would indicate that in fact you have a lean
> condition, not a rich condition.  Given high CO readings something
> doesn't smell right.  High CO (and really high CO in some of your
> data) indicates a lean combustion, since the lowest CO numbers would
> be acheived befor lambda of 1.00, and the highest (and yours are
> really high), after lambda of 1.00.  So, something is
> going on, but what?

CO or Carbon Monoxide percentage goes up when you have rich mixtures,
i.e. lambda less than 1.0 and it gets very low when you have lean
mixtures, lambda greater than 1. Possibly you are confusing CO with CO2
(Carbon Dioxide) but this gas tends to be peak near the lambda value of
1.0 and it drops off if you go rich or lean. My years as a licensed
emissions repair technician in California certainly drilled in the
basics of exhaust emissions.

The Charles Probst Bosch Fuel Injection book in Chapter 2 "Engine
Management Fundamentals" has the chart on page 6 (fig 2-8) shows the
relationship between HC, CO and NOx for changing lambda values before
and after the cat converter.

I have two graphs showing these relationships of the exhaust gases and
air/fuel ratios on my web site at

http://www.teleport.com/~scottmo/ecu20v.html#o2
 
> Could these high CO values indicate that combustion might be occuring
> somewhere other than the combustion chamber?  I think so. 

The high CO values are indicative of a very rich mixture, plain and
simple, but yes, it is possible to have combustion occurring the exhaust
manifold/turbo/downpipe. In some vehicles this is enabled typically by
introducing additional air into the exhaust from an air injection pump
system  to facilitate this burning.

> But not sure where
> you are getting your fuel mixture values from.

The fuel mixture values are calculated by an algorithm in the exhaust
analyzer which uses the 4 gas readings to make this calculation. A 1965
SAE technical paper #650507 "Air fuel Ratios from Exhaust Analysis"
describes how this calculation is done. 
> 
> Regardless, a bunch of us old v8 carb owners know, long term increase
> in HC fouls plugs, so eventually you will have a misfire in your 
>ignition system.

Well, that may be true back in the days of point/condensor ignition
systems and carburators, but with Fuel Injection and electronic
ignition, there are fewer problems with the ignition system and with
plug fouling.

> It only takes 1 plug of the 5 for HC to start a dripping, once that >happens, life gets complicated and expensive.  

Yes, remove one spark plug wire at idle, and you can see the HC and O2
levels skyrocket when you have the exhaust analyzer sniffer connected,
take the car out and drive it under load with this misfire, and you
might want to use the cell phone to call Midas Muffler to order that new
catalytic convertor. 

>Betcha a whole bunch of lawyers would have a grand interest any >technical explanation of raw HC's thru an exhaust system.

Yes, if they work for the EPA, they certainly would be interested, one
of the main reasons we have OBD-II is to add the ability to monitor and
record engine misfire conditions, this is done with sophisticated
algorithms that look at the time interval between firing events using
the crankshaft sensor. You also have to use the ABS system to monitor
wheel speeds, to sense changes in wheel torque applied to the engine
which are often encountered when driving a manual transmission vehicle
on rough dirt roads....OBD-II also incorporates the ability to monitor
catalytic converter efficiency by adding a second O2 sensor after the
cat.

> Very interesting numbers you got Scott.  I'd love to get those >printouts to explore them some more.  

I plan to enter them into a spreadsheet, so I can email them to you
sometime later this week.

HTH
-- 
Scott Mo.
1989 200TQ
1988 5000TQ
1966 VW Beetle
http://www.teleport.com/~scottmo