AFM Removal Tutorial.
 

Since I first mentioned that I’d removed the AFM on my '92 back in December I’ve gotten a few p-mails asking about the setup, and I’ve promised those folks that a writeup is coming. My apologies for the delay, insert generic excuse here.

At any rate, it's finally done. I've been running with the AFM removed for about a month now, and it's going quite well. I've given this its own web page due to the graphics-intensive nature. You can find it here:
http://miatajoe.50megs.com/index.html

Perhaps this will finally earn me the coveted Sticky Thread for which I have longed O' these many months. (Hint to moderators :D)

Edit: Geocities sucks. Site moved to new host.


UPDATE: musanovic has now done a version of this for the NB (which may work with the 1.8 NA) here: http://www.rpaperformance.com/miatamaf.html

I cant view that outlook site....

Even though i don't have an NA that was a hell of a write up.
+1 for making this a sticky.

I had to copy and paste the url into my browser, clicking brought up an outlook site as well.

Link asks for username and password.
Copy/pasting works.

hrk

heres the clean link
http://www.geocities.com/thraddox/AFM/index.html

I hope all of those things under "about the author" aren't true...

Dammit. Now I'm getting a "site exceeded data transfer limit" error...

I gotta find a new web host. Hopefully this will be back online shortly.

He has been knifed in a London subway, tear-gassed by the Michigan State Police, narrowly avoided a terrorist bomb at a theater in Tel-Aviv, and was once denied service at a Howard Johnson's restaurant.

you boner! :gay:

Ok, sorry about all that. I've temporarily moved the site to a new host:
http://miatajoe.50megs.com/index.html

Tonight I'll try to migrate it to a permanent server. Damn Geocities...

hey joe I made a mirror, if you want I can leave it there forever or until you find a home for it.

http://jazz.sdsc.edu/miata/afm%20index.html

wow you kick ass joe perez, thanks for the read, doess this go for the 1.8 miata as well?

holy crap dude that's a lot of work. there's absolutely no way I would have the time/energy/patience to do that.

What are your driving impressions?

The basic principles are the same, however it would require an entirely different map. For one thing, the hotwire sensor that the 1.8s use is non-inverted, meaning its voltage output rises with increasing airflow. This is in contrast to the 1.6 flapper-style AFM where the output decreases with rising airflow.

More importantly however, the airflow vs. MAP/RPM characteristics for the 1.8 are going to be a lot different. Not only is the engine larger, but it has different cam profiles, a different head design, etc. I suspect that you'd actually need different maps for the different 1.8 head styles- one for the '94 to '97, one for the 99+, one for the variable intake cam...

However, if anybody has a 1.8 Miata they'd care to loan me for a few weeks, I'd be happy to generate the data for it. :bigtu:

That's why I did it for you guys. :D

Well, I was a bit discouraged by the initial hesitation problem, but that seems to have been cleared up by the Accel map. I suspect if I had a real TPS I could have dealt with it more elegantly, but such is life.

I have not really noticed any serious change in driveability, which I consider to be a good thing. One benefit is that I'm now able to run my BOV direct to atmosphere, through a K&N filter of course.

My biggest gripe with the AFM was that after I'd installed by BOV the fuel pump relay would click off and on a few times every time I shifted due to the flapper banging back and forth. It did this even after I plumbed it for recirculated, which puzzled the hell out of me. Fortunately this didn't cause any serious problems, but being toggled every single time I shift can't be good for the relay contacts. Switching a big DC load like the fuel pump causes relay contacts to degrade, which is the typical cause of failure for these devices.

Awesome job. Glad you got it sorted out. I spent a little time with it but gave up soon after aquiring the TEC3. Get a auto TPS, you will thank yourself. Using that with the accel enrichment maps made my car perform very well, no tip in or stumbles.

Hello Joe,
great write up!!

2 points:

1: whats the reason why the 2 bar sensor dont work correct?
From the data, it should deliver same results.

2: The hotwire 1,8 Airflow Meter ( is ít still a AFM?)
dont restrict the inlet that much and need not a lot space.

I remember, with the Ultimate its easy? possible to use a 1,8 AFM
on a 1,6 system with 1,6 ECU. Is that correct?


Falk

For one thing, the output of the 2 bar sensor was a lot noisier. Individual intake pulses were showing up as huge spikes in the output. It's almost like the Greddy sensor has some built-in dampening to ensure that it produces a smooth output.

Secondly, the EMU software limits you to dealing with a voltage range from 0.5 to 4.5 volts, which is what the Greddy sensor produces. The 2-bar MAP sensor operates from 0 to 5 volts, so it's off the scale at very high vacuum and at very high boost.

The 1.8 is technically a MAF (Mass Airflow Sensor) and you're right, it's a much better design. I probably wouldn't have bothered with this whole project if I had a 1.8 ECU.

I've heard people say that this is true, and there is a drop-down for it in the vehicle parameters tab, but I don't see the BP or B6(NB) sensors listed, so I don't know if Greddy has actually coded the data for it.

You could do it via the same method- namely connecting it to the AFM input and selecting AFM(v) in the Airflow Map, but since you couldn't log both sensors back-to-back that way I'm not sure how you'd generate the basemap.

It might also be possible to use the Analog Input-Output wires for this and just do a 1-d map, but again, I'm not sure how you'd do the initial logging without some external equipment. I can't seem to enable Analog Input on the logger screen.

I got a chance to log Joe's AF Output map against my RX-7 AFM. Looks really close.
http://www.systemstrategies.com/miat...versus_MAP.jpg

The dyno also showed about 1 pound of boost improvement. The only thing I can attribute that too is the change of AFM to the rx-7 and larger filter. Can't wait to get rid of the AFM completely.
Log file attached

:bigtu:
Seem to have my initial "issues" cleared up. I guess my car pulls a little less vac at idle than yours?

I set the first column to 650 rpm and raised the voltage output in the -12.3, -10.1, and -8 cells in that column... Seems to be running well, pretty nice idle, and right now I'm running 0 injector in that area, but I may end up running a little correction due to my big 550s.

Joe,

Thanks for this mod!!!!!! It has produced somewhere between 1.5 and 2 PSI FREE BOOST on my M45 blower.
--Chris
You can read all about it here.

http://www.systemstrategies.com/miat...takeAfter2.jpg
http://www.systemstrategies.com/miat...odDownSide.jpg