The issue for the OBD I, built before 1996 and after 1971 it is possible.
The EPA rules will not allow any shop to modify any certified car or truck.
Individuals can make modifications for off road usage.
Even some manufactures used resistors to make mixture changes at temperature points, BMW added a resistor to 1977 to 1983 M30 cars to fix idle issues.
After 1996 the OBD II computers are required and the systems now are smarter. If the ECU gets a signal it is not expecting it can decide to not use that signal and even replace the sensor imput with another different sensor. Most OBD II check engine lights are not apparent since the car will be running fine.
I hope this helps.
Now on older cars there are companies that make controllers and PC controlled add on processors to allow changes to be made.
On my e24 I have added a Split Second controller that allows me 4 points to set the AFR on my car.
The controller is in the glove box, and is indexed to allow me to play with settings and get back to smooth running.
Here is the Ford 65mm MAF and it is made in JAPAN.
If this engine was shiny enough to reflect,
you would see me smiling while taking the pictures.
Cause I really like the output of the MAF.
Six hours, DIY, including the indicator and can switch back to AFM in 2 minutes, Two screw clamps on MAF, two quick electrical connectors and the OE connector is tie wrapped back out of the way.
OE is
3430cc M30
Motronic
DME II
92x86, 8.0:1
185bhp/5400rpm
214lb.ft/4000rpm
I own a dyno so here is the output at the wheels.
HP loss in transmission and differential 25%
So 222 HP at shaft is the result.
I am using the J C. chip also, a 3.71 ratio, with 265 Getrag.
The sweet spot of the m30 is now at 2200rpm where it was at 2800rpm.
That is the point where the rumble of the exhaust resonates in frequency with the intake. On the unmodified it is only seen on the cold mornings when the fuel system adds a little more fuel and the cold air is giving it's all.
I really like it.
My Cartech RRFR installed and test in advance of the M102 12 psi turbo.
I hope to sneak up on a few Stangs and Meros on the Dyno.
My source:
http://www.bmpd.com/bmw/parts/catalog/engine_32.shtml
Later,