We're finally warming up to the 50s in upstate NY.
Doug Fedeli
"Sevrence, Sean (S.J.)" wrote:
> 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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