1 Bar, 2 Bar, and 3 Bar MAPS

[Mike Pitts]

<<Has anyone used / tried a 2 or 3 bar MAP sensor?   I have a '95 Chevy 1/2
ton truck with a small blower making 9 lbs of boost, and I'm thinking of
trying a 2 BAR map sensor from Accel.   I assume all I'll have to do is
adjust my fuel settings.   I'm also assuming the stock computer won't throw
a fit with it.>>

You can't just change the MAP sensor, it will throw 
*everything* off. Almost every table in the PCM is 
indexed directly or indirectly from MAP.  Including 
some of the transmission tables (if you have an automatic). 
Try it, and you'll immediately see what I mean.  :)

IMO, the correct way to switch to a 2 or 3 bar MAP is 
to write a code patch that scales the new MAP's readings 
back into the 1 bar range for all of the existing tables 
and code.  But store the actual boost reading in RAM 
for your own use, if you want to increase injector DC 
or reduce timing.  This is what I did for my 93 CPI engine. 

It ain't easy though.  I spent every evening and every 
weekend for at least 3 months straight reverse engineering 
my PCM code before I had enough insight to make the code 
patch.  I would guess somewhere in the range of 300-500 
hours so far.

Unless you are prepared to write code patches for your 
PCM, you're better off just sticking with the 1 bar MAP 
and using the whatever you currently have to add the 
additional fuel for boost.

-Mike