The sensor signals are put into the PCM which calculates it and compares
them to reference values (expected values). If they're within normal range
(throttle position, MAP, vehicle speed, for example)...the calculation runs
as posted. On the newer vehicles (starting in 2002), the PCM can insert
it's own values if a sensor if out of range. Example: Disconnect the Crank
sensor on an '05 Dakota and it still starts and runs - the MIL is tripped
but the PCM inserts its own value to get you down the road to a shop for
repair. The ETC engines can also run without the MAP and Crank sensor
installed.
On the '07+ 3.7/4.7/5.7L engines, you can try to "tune" the PCM with a
piggy-back system but you'll never get it right. The PCM only looks at the
MAP sensor for initial BARO reading - once that's done...it works off of
internal, calculated values.
In the 1992 case, they're not that elaborate but expected values are still
in place. Modifying something like the IAT can't affect mileage that much
since there's a 33% Fuel Trim allowance. The PCM will try to get a close to
"0" by calculating the difference in between the LTFT and STFT. This is why
modifying an IAT sensor really doesn't do a whole lot to mileage unless you
go way out of the normal/expected range.
On the fuel adaptives...there are 26 different tables which correspond to
MAP and Engine Speed. All of them use calculation formula.
- Bernd
-----Original Message-----
From: Phillip Batson [mailto:pbatson68@yahoo.com]
Sent: Saturday, September 20, 2008 11:12 AM
To: dakota-truck@dakota-truck.net
Subject: DML: RE: Cold engine puts out more hp/tq...
Are any of those variables calculated or are they all readings from sensors
on the truck?
Another way to ask this is, does the computer just take sensor readings and
plug them in for the calculation, or does it have something like reference
tables in its programming to calculate certain values that may exceed
certain limits? So, if it gets a reading for say, upstream 02, and it is
outside some set range, does it modify what it plugs into the equation?
If so, that would really limit the 'effect' any one variable has on the
equation if there are limits setup for different (or maybe all) variables.
----- Original Message ----
From: Bernd D. Ratsch <bernd@dodgetrucks.org>
To: dakota-truck@dakota-truck.net
Sent: Friday, September 19, 2008 8:58:52 AM
Subject: DML: RE: RE: RE: RE: RE: RE: Cold engine puts out more hp/tq...
Yup...while yes it can, it depends on quite a few other conditions - not
just intake air temp.
(RPM/Max RPM) x (MAP Baro) x (TPS x ECT x IAT x Sensed Battery Voltage x
LTFT) x (Upstream O2) x (STFT x LTFT) = PW
That's the formula. The ignition timing is also affected by IAT (but not
just by itself) so engine and weather conditions do apply. Higher/Lower
pressure, engine coolant temp, engine rpm, battery voltage, throttle
position...so you're trying to tell me that they don't matter??? What about
what the O2's read - think about those variables and how the PCM reacts too.
Fuel mileage is dependent on a lot of variables - yes...the difference in
between a 30 degree outside ambient and 90 degree outside ambient will
affect mileage slightly, but again...pcm calculations need to be figured
out.
- Bernd
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