[Diy_efi] RE: Diy_efi digest, Vol 1 #413 - 12 msgs

[Adam Wade]

--- Dave Dahlgren <ddahlgren at snet.net> wrote:

> When you use the 4 gas machine do you get different
> readings when the timing is incorrect?

Well, depends on what you mean by "incorrect", but
yes, you can see definite and predictable changes in
the gases based on where the ignition timing is set.

> Can you illustrate the set of conditions and what
> you might see and then if you moved the timing what
> might happen to the readings?

Well, keep in mind that every engine is going to have
slightly different readings, because of intake and
exhaust tract resonances and efficiencies, cam timing
(duration and lift included), combustion chamber
shape, swirl, fuel atomization, and on and on...  So
you'll never see the exact same readings on any two
different types of vehicles.  Once you do one or two
of a particular vehicle you can establish a baseline
and tune to it, which will get you within a few
percent.  Before you get a "baseline" and then tweak,
you would have to use basic tuning techniques of
overshooting and then coming back, which would take a
little bit longer (but especially with EFI, where you
can usually tune in real-time while on the dyno under
load, it's not much longer).

After that, if you know basically what a particular
combustion chamber is going to show you, the rest is
down the combustion science right out of the book.  If
your ignition timing is too late, not only will you be
down on power, but you will see increased unburned HC
and O2 in the exhaust, with lower NOx, but similar CO
to "correct" timing.  Too far asvanced will have low
HC and O2 numbers, higher NOx, and again the same CO,
as a rule of thumb.  Obviously there is some
variation, but that's the basics.

> I am thinking that the WBO2 reports what it sees but
> what does the 4 gas see in the same situation that
> would make you think that it is timing related
> rather than fueling related.

See above.  CO is what I've found to be the best guide
for mixture.  Being able to correlate HC against O2 is
also a very important tool, but differences in intake
tract, fuel delivery, and combustion chamber will add
some variation.  It's fairly easy to see timing, since
HC and O2 change together, and CO does not vary by
much.

> The WB is seeing inefficient combustion hence the
A/F
> ratio being skewed what parameter in 4 gas would say
> the fueling is correct but the timing is off?

See above.  I cannot tell you how much easier a
four-gas makes things in terms of being able to
determine what's going on inside the combustion
chamber.  Again some "reverse inference" is always
going to be necessary, since this is an indirect tool
and not a perfect predictor.  But it's a very useful
tool, epsecially when you know what you're looking at.

=====
| Adam Wade                       1990 Kwak Zephyr 550 (Daphne) |
|   http://y42.photos.yahoo.com/bc/espresso_doppio/lst?.dir=/   |
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |

__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com

_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi