some background. My car is a 1982 Balocco SE with a 3.0 engine
from a Verde (with typical street modifications like ported
heads, cams etc...).
performance modifications I ran across a guy who builds racing
Porsches for a living and specializes in fuel injection. The
cars he builds race at Sebring. Anyway, this guy just happens
to be an Alfa nut and has built some seriously fast GTV/6's
and Milano's. One of the first things he told me was the Bosch
AFM was a giant restriction to the intake of the engine. The
best thing to do was to find a way to get rid of it all together,
but that would require an upgrade to a Haltech system (or
best would be to replace it with a similar but larger Bosch
AFM. Best place to get one is from an old BMW 63X or 73X.
So I get one of these AFMs from a BMW 733 at the junk yard
for about $50. It looks pretty dirty so I decide to tear the
thing apart into little pieces to clean it, paint it and lubricate
any moving parts.
message I'd like to get across to my fellow Alfa brothers
is this: DO NOT FEAR YOUR AFM!!! It is a ridiculously simple
contraption. I've read dozens of posts from people warning
others not to open or adjust your AFM -- black Voodoo magic
inside. I say BS. Tear one apart for yourself and you'll see
what I mean. The thing is basically a box with a spring-loaded
flap on the inside. Attached to the top of the flap is a variable
resistor which has a number of positions on it.
thing to know about the resistor is that it is not infinitely
variable between its lowest and highest values. I think it
has about 10 possible values it can report back to the ECU.
It also has a built-in air temperature sensor. I'm sure you've
read a few posts about making adjustments to the spring settings
inside your AFM. "Loosen it a few notches" etc... All this
adjustment is doing is changing how fast the air moving through
your AFM will push the little resistor over to a higher or
lower value setting for a given amount of air -- which equates
to a richer or leaner mixture (theoretically).
ahead here, but it is also important to know that your ECU
has the power to adjust the mixture itself up or down as it
sees fit. It does, however, have a limit to how much it can
adjust the mixture based on the information it is given. As
a result, a minor change to your AFM spring control may or
may not have any impact on your mixture. The bottom of the
AFM is held on by little rivets that are cast into the assembly.
If you take a little Dremel tool (grinder) you can grind these
little nubs off yourself. Carefully pry the bottom off by
sticking a screwdriver or something into both openings of
the AFM to work it loose.
re-attach the bottom of the box with a hot glue gun to place
little spots of glue where you ground out the rivets. As for
the electrical parts, I tried two different configurations.
I tried the BMW components as is, and I also tried the components
from my Alfa AFM transplanted into the BMW AFM body. Guess
what? They both worked for me. I even tried combinations of
my Alfa ECU and a BMW ECU (which I found to work best). You
will notice that the BMW unit has more connectors than the
Alfa unit. Don't worry about it.
want excruciating detail about how to diagnose and troubleshoot
the Bosch L-jetronic system and/or AFM, I refer you to a great
book called "How to Understand, service and modify Bosch Fuel
Injection & Management by Charles O. Probst. Robert Bentley
Publishers. ISBN 0-8376-0300-5 To get the larger AFM to fit
into the Alfa intake hose, you'll need to heat up the hose.
One guy I talked to put the whole thing in the microwave to
heat it up. My solution was to boil a large pot of water and
submerge the end that I was trying to heat up. With the hose
very hot, stuff the AFM into the hose and let it cool down.
A little Vaseline will help too. You'll notice from my pictures
that I painted the BMW unit black with spray paint just for
also notice from the pictures that the BMW unit is significantly
larger than the Alfa unit. See for yourself. Another important
tip that I want to communicate is that you will most definitely
need an air/fuel mixture gauge before you try this modification.
Buy one and mount it on your dash. They are about $100 and
are really easy to install. 12V Positive, Ground and one more
wire to splice in to the wire coming from your O2 sensor in
your exhaust system. If you think you can safely screw around
with your fuel system without some kind of gauge to tell you
what you have done to your fuel mixture -- think again. Don't
do it. Your original air cleaner assembly won't work any more
because the hose won't line up with the opening to the air
cleaner. Take the top part of the air cleaner off and throw
it in your garage.
kind of padding (like a piece of foam rubber) for the new
AFM to sit on top of the bottom portion of your existing air
cleaner -- until you get really creative and figure out how
to permanently mount the new AFM. There is a K&N filter available
(I don't know the model number) that has the exact opening
size as the BMW AFM. It costs about $50. I love the added
"intake noise." The car sounds faster...
you will also have to modify your idle speed and your idle
mixture. The idle mixture is an Allen screw in the AFM itself.
Using your Air/Fuel gauge, let the car idle (at temp), then
adjust this screw until the mixture is correct. Hope this
is all helpful to anyone wanting to try this modification.
It's really very easy compared to other mods. And if you don't
like it, you can always put the original unit back on. Good
luck and happy motoring!