LOL Looking through the eyes of a Texan "really cold days (50 or below)"
Sorry Bernd! The door was open on that one ;^P
Sean
'92 RC Sport 3.9L 5spd - 250,000mi!
'01 CC SLT+ 4.7L 5spd 3.92 LSD Mobil-1!
-----Original Message-----
From: bernd@texas.net [mailto:bernd@texas.net]
Sent: Wednesday, April 04, 2001 9:10 AM
To: dakota-truck@buffnet.net
Subject: Re: DML: IAT and the 4.7L
Hehehehehe....ok Shane, I basically said the same thing...in 50 words or
less
though. ;)
But Shane is correct as well...the IAT Adjuster ONLY works during Open-Loop
conditions. In Closed-Loop, you're at the mercy of the PCM. Other key
point,
relocating the IAT works almost as well but the fine tuning is where my box
comes in. You can run either way...but on really cold days (50 or below)
you
won't notice any big improvements as compared to a hot day (70+).
- Bernd
> Aajaynefour@cs.com wrote:
>
> > I believe this topic was discussed about a week ago, but the results
seemed
> > inconclusive. The IAT, as I understand it, is a variable resistor that
> > responds to temperature changes in the intake air stream and sends a
voltage
> > to the PCM that is used to select the "optimal" air fuel ratio.
>
> It is used as a variable in a formula to find the mass of the air entering
the
> engine. MAF-based systems attempt to measure the amount of air actually
entering
> the engine, MAP-based systems attempt to calculate the amount of air
entering
the
> engine. One of the sensors used during the calculating process is the
IAT.
Once
> the calculating is complete, the PCM uses the calculated mass of air to
determine
> what the fueling requirements of the engine are at that particular time
and
> schedules an injector pulsewidth accordingly.
>
> The calculating process is only occurring during open-loop mode (WOT and
> transients).
>
> > So far so
> > good. Bernd has developed a simple but effective way of sending a
"false"
> > voltage to the PCM making it think that the air is cooler than it
actually
is
> > and thereby selecting a different (richer ? - more performance biased)
fuel
> > curve.
>
> Only under WOT or transients (open-loop mode) can it "select" a different
fuel
> curve - and then it is only shifting it (rich or lean) by a finite amount.
>
> > Still good. My questions are as follows: Does the IAT in the stock
> > location react to air temperature changes to maintain a stoichiometric
air
> > fuel ratio?
>
> No. Closed-Loop mode (where you spend most of the time) is an O2 feedback
> control loop which attempts to maintain a stoichiometric (14.7 to 1) air
fuel
> ratio. This is done primarily for emissions control. The best
> power/torque/horsepower is said to occur around 12-12.5 to 1 ratios.
>
> > If so, then basically Bernds IAT adjuster causes the PCM to
> > deviate from stoichiometric in the direction of a richer mixture as the
air
> > temperature and therefore density stays the same.
>
> The PCM will never deviate from stoichiometric (unless you modify the O2
sensor
> signal) as emissions control (not performance) is its main goal. This
only
> applies to closed-loop control mode. In open-loop mode it can only guess
at
the
> fueling requirements. Bernd's device modifys this guess.
>
> Before attempting to modify the PCM's fueling strategies - I would
recommend
an
> A/F gauge as an insurance policy. Most people are already too rich
(during
> open-loop). Most people relocate their IAT into a cooler location.
Problem
with
> that is - richer isn't going to help - instead it hurts. During WOT or
> transients (passing, pedal stabs, decel, etc) on the other hand, can
provide a
> perceived improvement. At the dragstrip or on the dyno (both WOT) it may
show a
> slight improvement. But in daily stree-driven usage - it only makes for a
sooty
> tailpipe and poor performance.
>
> My $0.02,
>
> Shane
>
> --
> '96
IndyRam-HisIndy-MPI/TB/Pulleys/AccelCoil/MPComp/HookerSuperComps/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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