IAT range

[Bruce Plecan]

>  If I understand correctly, the IAT relocation mod is supposed to
> place the IAT in a cooler location, thus tricking the ECM into richening
> the a/f mixture.  But, is this what we really want?

I really varies by application to a certain degree.
On the Cat'd cars they cycle over and under the 14.7 to keep the converter
happy.  While on alot of engines you can run atta steady 15.5+:1 AFR (at
idle / cruise, and still be fine (other then in flagrant vilation of the
EPA)...
   On some applications (747 MAP) (some 730s MAP) from full cold (-40) to
normal operating temp there might be 6% difference in fueling.
   As mentioned inna nother post there is alot of hot restart stuff that
depends on knowing the correct MAT.  (Difference is in sensor mounting, when
on the manifold it's Manifold air temp, and if eslewhere in the intake tract
then it's Intake Air Temp.)..
   One other factor that was brought out by Scott S some time ago was hot
soaking.  That has to be right, or your going to be in lots of trouble with
cutomers on hot restarts.  Folks were getting almost violent over some
problems on the 87 MY 3.8Ls when they first came out.  I think is was just
the first few hundred but marry hell was paid in getting that one right.
Any way, hot restart and full lock on the streering is like Mrz. so and so
leaving the market.  With ice cream thawing, it's hurry home time.

  Now, with all that said about the IAT/MAT:
  There is some hope:
What **MIGHT** work is lieing to the ecm about engine temp. If the ecm
doesn't control the rad fan, or if the fan's operation can be divourced from
ecm control you can slightly tinker with the CTS.   But, there are some
absolutely critical items that depend on it meeting a min operating temp..
Like most all the **CUSTOM** chips that require changing thermostats, that
is what in effect they are doing.  What can be done is add a inline resistor
to the CTS, to let the ecm think the engine is at 160 when in effect it's at
190.  Using a 220 ohm resistor might work for that.
   I've been known to use a pot with an inline resistor with a switch.  That
way Switch open I can run run a min temp like 160 and if the port is like
5-10K then I can deal in some more richness.  Wound up being the only way I
could drive the car once after getting a tank of crap gasoline.
   **BUT**, I knew where I was with what the min temps were for things to
operate.
Grumpy
   Remember free aadvise may not be EPA legal, and your responsible for
tuning your engine, not me

 I was under the
> impression that, from the factory, most a/f mixtures are more towards
> the rich side already to keep the cat cool and reduce the formation of
> NOx, especially since the Quad4 does not utilize any measure of EGR.

Dual overhead cam 4v per cylinder probably can run better self egr'ing
control in the mechanical design of the engine and get away with out the
EGR.  Also, with a central plug, and at least a pentroof type chamber should
be able to get by with less *needed* timing then in a wedge, so again more
leeway due to engine design characteristcs.  However, I not saying they are
running alot, or min amount of timing at idle cruise, too hard to figure out
what was going thru the calibration guys heads.


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