[Diy_efi] MAF Question

[Daniel R. Nicoson]

Bill,

The computer has a "lookup" table (called the MAF transfer function) in its
code that is specific to the stock MAF.  When the MAF sends a 1.3 volt
signal to the computer, the computer looks up 1.3 volts to know how many
kg/hr of air is entering the engine at that instant.  Then the computer
calculates a pulse width for the fuel pulse based on the injector size.  The
injector size is also stored in the computer.

To do it right, you would need to enter the proper MAF function for the
Mustang MAF.  Then when you installed the Mustang injectors you would need
to enter their low slope, hi slope and injector breakpoint values.  Then the
computer would be fairly happy and the car should run pretty good.

The aftermarket, typically Pro-M, will "calibrate" their aftermarket MAF to
work with the size injector you want to use.  Their process of calibration
gives a voltage from the MAF based on their library of stock MAF functions.
This process "tricks" the computer with its stock MAF function into
calculating the "correct" value of air entering the engine.

On some motors this works OK.  On my 1994 Mustang GT it did not work OK.  We
could get the car to work OK at WOT but part throttle sucked.  Massive
pinging at part load...  What was happening was that by "tricking" the
computer with the MAF signal the computer thought the engine was at a very
low load and it gave a ton of spark advance.  In fact the engine was at
60-70% load and couldn't use all that spark advance.  The computer needed to
have the correct MAF transfer function to work right.

My solution was to get an EEC Tuner.  This device allows you to tell the
computer the "truth" (proper MAF transfer function) and to let the computer
work correctly.

In your case I would first decide if you really need to add a bigger MAF &
injectors.  If you are just looking for 10-15 Hp, get a noisy muffler and
enjoy a good factory tune.

If you are adding more power than your current MAF/injectors can handle
(turbo or supercharger) then you will have to make  changes similar to those
I described.

It is a lot of work and takes lots of time to re-tune these things even with
the EEc Tuner (or Tweecer - another 'tuner).  The thing we enthusiasts don't
have is the Ford dyno room.  They actually do a very nice job of tuning at
the factory.  If you are ready to go to work on it, check out the Yahoo
groups EECTuner/TwEECer forum.

Have fun,

Dan Nicoson


-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]On
Behalf Of va3xcd at sympatico.ca
Sent: Thursday, June 05, 2003 2:28 PM
To: diy_efi at diy-efi.org
Subject: [Diy_efi] MAF Question


Hi Everyone,

I am new to the list, and so this is my first post.
I must say the calibre of people I have seem posting
here is impressive. I hope I can contribute my share
back, but I am still new to this stuff.

I do have a question:

Car: 1998 Escort ZX2
Engine: 2.0L Zetec

I would like to increase the size of the MAF, as
well as the throttle body. Is there a way I can
change the MAF to a larger unit without
recalibration? Am I right in thinking that if
I also change out the injectors to a set that
is matched to the MAF I can get away without
recalibration? EG: Mustang MAF and injectors
for example (I dont know if they are a direct
fit....just used that as an example).

Finding all this a little overwhelming at this
point, as I am just starting to understand the
way these systems work.

Any help would be greatly appreciated...

Regards,
Bill


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