a MAF too small

[Frederic Breitwieser]

| I have an 89 5.7l Iroc, 165 ECM, ARAP (vette) binary. I have put a
| supercharger on it and the computer has no idea what airflow is
| coming in after about 3000 rpm cause the MAF reads 255 right about
| there.

When you double the airflow into a MAF based system, the MAF will of
course max out at about 1/2 of redline, so what you are experiencing is
a reasonable "irritant" considering what you have described.  There are
many ways to fix this, one is to recode the eeprom in the ECM, one is to
play with fuel pressure, change mafs, and do other funky stuff, however
there is an easier solution.  Someone either here or on another list
mentioned this to me, I ignored and discounted it, but after testing it,
success was achieved.

Create a bypass for the MAF.  Simply run a tube at a 30 degree angle off
the pre-maf tube, connecting to the post-maf tube, also at a 30 degree
tube.  By increasing the diameter of this tube, less air will go into
the MAF, thus produce a lower reading.  I did this successfully by
doubling the airflow, doubling the fuel injector size, and it worked
well, except at idle.  Idle would rock between rich/lean/rich/lean and
become annoying.  The solution to that was to have a spring loaded lever
on a valve that reduced the airflow in the bypass tube during idle, and
open the second you tap the gas.

Took a lot of tuning as far as hose diameter, playing iwth the valve,
and the car in question still idles a little strange, however when the
supercharger kicks in, its a blast to drive.  Also, there were no
modifications to the ECM or the wiring harness, which makes it easier
for people who don't have the ability to rewire or change code.

Hope that helps.  Before you change things around, you have to do some
math... I just said "double the injector size" and that might be way
off, it was merely to illustrate the concept more than anything :)


-- 

Frederic Breitwieser
Xephic Technology
769 Sylvan Ave #9
Bridgeport CT 06606

Tele: (203) 372-2707
 Fax: (603) 372-1147
Web: http://xephic.dynip.com/