'MAP' and Fueling

[Bruce Plecan]

| I'm new to the group and have a few (probably) simple questions. (Sorry
it's
| a long Email)
|
| What is the relationship between MAP and MAF. RPM and Air Temp are factors
| in converting the MAP sensor output to match the MAF. What I am trying to
do
| is understand what the differences between MAP and MAF are.

MAF directly measures the amount of air entering an engine.
MAP is used to calculate the amount of air entering an engine.
It's a wash for which is better. They both have advantages and faults in
theory.
Really a matter of what you perfer, and most comfortable working with.
I just happen to like MAP.  While it's not seemling as adaptable as the MAF,
it's easier for me to understand, and work with, so I have my best results
working with it.  It also, is better for transiant responses, so with my
analness about responsiveness, it works for me.

To me ain't nothing more important tehn not running out of resolution, and
table room for tuning.  Tuning an engine to run 18 PSI of boost with a
calibration that stops at 15 PSI, is just plan dumb, or worse in my book.
Means that at either less than WOT the calibration is wrong or at WOT it's
wrong, your choice.  Both are losers in my book.  Hate to be blunt, but
that's how I see it.
Grumpy
   Like I just said in another posting try the archives at DIY for MAP, and
MAP, there is a ton in print about it

| I have a Toyota Supra Twin Turbo and they come with both MAF and MAP
sensor
| systems for the export and Japanese spec cars. These cars have a fuel cut
| which operates as soon as the manifold pressure exceeds a preset limit of
| 13psi. I have designed a voltage hold circuit which clamps the output of
the
| sensor at 13psi (about 4.3V) and hence fools the ECU of the car into
| thinking it is running much lower boost from the turbos.

| The problem is that I am unsure if this will affect the fueling
| charateristcis of the car if I have modified the MAP input the ECU, above
| the 13psi limit. I may be having fueling problems but am unsure what I may
| have done.
|
| Thanks for the reply from Ric Rainbolt regarding the issue. I have
| faithfully added his Email below.
|
| *****P.Betts***********
| The US Surpa site say modifying the MAP sensor output with a fuel cut
| controller is a bad idea for the Jap spec MAP sensor cars but I agree with
| Rob below. As the Supra runs rich at high boost the inability of the ECU
to
| correctly calculate the fueling above fuel-cut, because one of the inputs
is
| static, is small up to a point.
|
| The next question is at what point (manifold pressure) does the MkIV (and
| MkIII for interest) start to lean out? This is probably why water
injection
| makes such a difference because the fuel that is available is cooler and
| thus able to deliver power to the engine more efficiently. (More
| effieciently burnt)
| (Time to get a second oxygen sensor or monitor the current one)
|
| So as a summary.....
|
| The Jap spec Supra **CALCULATES** the Mass Air Flow going into the engine
| using the parameters described below, one being the Manifold Air Pressure
| (MAP).
|
| The Export (UK) Supra directly senses the MAF using some form of
| butteryfly/flap type arrangement (I think) and uses this for fueling
| calculations along with RPM (I suppose) The MAP sensor on the Export
models
| is only used to detect engine vacuum and pressure and doesn't directly
| affect fueling.
|
| Thoughts/Corrections anyone? Any guidance greatfully received.
|
| Thanks
| Pete
|
|
| *****R.Rainbolt*************************************************
| The fuel cut is used on both the Turbo Supra and Turbo MR2.  Since both
| cars run relatively rich at full (stock) boost, it is "safe" to use such a
| circuit to prevent the computer from hitting the fuel cut function, but
| only up to a certain amount of boost.  For the MR2, the FCD cuts in at 11
| PSI, but it is safe to run the car up to about 15-16 PSI, without fuel
| system mods.
|
| To be safe, the best thing you can do is get an extra Oxygen Sensor
| installed and connected to a dash meter (HKS, Summit, Greddy, etc.)  If
the
| FCD is set to 13 PSI, I would not go over 16-17 PSI. Make sure the car
| never turns from rich to lean under full power.
|
| MAP (Manifold Air Pressure) is directly related to MAF (Manifold Air
Flow).
|  The amount of air moving into an engine is refferred to as Mass Air Flow
| (MAF).  MAF is a function of 3 major factors (ignoring temp and humidity
| for a moment).  They are: Throttle Position (TPS), Engine Speed (RPM) and
| Volumetric Efficiency (VE).  VE is a complex component, being different
| values at different RPM and TPS levels.  Systems that only use TPS and MAP
| are referred to as Speed-Density (SD) systems.  They "approximate" the
| amount of air the engine is using computing MAF from the three above
| mentioned components.
|
| Toyota and other manufacturers use MAF and MAP sensors, even though it is
| not absolutely necessary to have both. Either will work, as long as TPS
and
| other factors are known.  On the MR2 and Supra, HKS sells a kit that
| actually lets you eliminate the MAF sensor.  The idea is to allow for
| better intake breathing and better throttle response.
|
| Ric Rainbolt
|
| **************************************************************************
|