"Bernd D. Ratsch" wrote:
> >From the temp readings on my OBD-II Scanner, the IAT sensor readings change
> constantly. Especially in Closed Loop operation.
I agree that the sensor is continuously changing values. This doesn't mean the
computer is using those readings to affect fuel delivery during closed loop. It
only uses the O2 sensor during closed loop control - hence the name closed loop
- feedback that is. Thats the only purpose of the O2 sensor - it feeds back to
the computer what the ACTUAL A/F ratio is allowing the computer to stay at or
near stoich or 14.7 parts air to 1 part fuel. Unfortunately this is only best
for emissions NOT power.
> Under WOT, the computer
> does use set parameters so you are correct...to a point...but putting the
> IAT in a colder air charge does allow the Dak to perform better in warm
> conditions. (Seen that happen on most of the Dak's we've done it to.)
I agree...to a point. While in enrichment modes - you will get more fuel using
the IAT trick - but does that help performance? I don't know. I need some
evidence like dyno results or something. Anything but "...does allow the Dak to
perform better..." -or- "Seen that happen...".
Since dragracing usually involves WOT operation only - the factory rich (overly
rich) mixtures are enough for me. Too much in fact - more power is available if
LESS fuel were given via the injectors. Ever notice how just less than WOT
seems to pull harder? Thats because closed loop is probably closer to the best
power (12.5 to 1 or so) than is the factory rich WOT mixtures (depending on
mods). An A/F gauge will show you that.
> During cruise conditions, the TPS, IAT, MAP, O2, CTS (Coolant Temp Sensor),
> and other "variables" come into play as well since there is never a
> consistent load on the engine.
Any time you change the TPS by a large amount - you go into an enrichment mode.
Either positive enrichment or negative enrichment. This means more gas or less
gas corresponding to more throttle or less throttle. You can watch the result
of this behavior on an A/F gauge. During enrichment modes - IAT, MAP, and CTS
are indeed referenced. If the delta-TPS is stable for even a few seconds - the
computer "closes the loop" and uses NOTHING but the O2 sensor to determine fuel
delivery strategy.
> Yup...one of the readings on the scanner is
> "Engine Load"...Not to mention fuel-trim%, O2 sensor voltages (all of them)
> and quite a few other readings as well. (About 35 of them)
On your scanner "Engine Load" is the MAP and fuel-trim% is this enrichment I am
referring to (short term FT that is). Yes - scanners are cool. I have one
also. I am in the process of writing my own. ISO-9141-2 to RS232 hardware is
getting cheaper everyday (less than $50). If you would like to know what all is
involved in building a scan tool from scratch - or what procedures you can use
to diagnose problems with yours - check HS-3000 (a book) from sae.org - around
$79. I'm not assuming you are having problems or anything - just thought you
might be interested.
A/F gauges are cool also - and much cheaper at around $39 - full blown fancy
jobber from Autometer 8-).
Latr,
Shane
-- '96 IndyRam-HisIndy-MPI/TB/Pulleys/Coil/Wires/CompTAs '96 IndyRam-HerIndy-numbered(#142)"Track Truck" '74 Triple-Black Dodge Challenger Rallye 360 home-brew EFI R&D vehicle '68 Black Corvette Convertible 427 (For Sale)
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