Tech write up - MX5-RX7 Hybrid AFM

[Uncle Arthur]

Decided I'd finally get around to doing this today, and found it so easy I decided I'd post a write up.....

Get your RX7 AFM and your MX5 AFM - if you put them together you will notice that wht footprint of each is exactly the same - the RX7 AFM is deeper and has a much larger cross sectional area, hence it will flow much better.

There has been quite a bit of talk about simply replacing the MX5 AFM with the RX7 unit, however the spring in the RX7 unit is much heavier, so others have tried to adjust for the MX5's lower capacity by easing off the RX7 spring, which also results in some issues at idle as the flapper door doesn't hold shut properly.....

The solution is to take the internals from the MX5 unit, and install them in the RX7 unit.....

So - back to the process.....

Tools you will need:

Hobby knife/razor blade
3 mm Allen Key
Phillips head screwdriver
Blade head screwdriver
6mm open end spanner
Soldering iron

Using a hobby knife or similar, cut through the silicone bead which surrounds the black plastic lid on each unit - it will then prise out easily enough using a blade end screwdriver. Inside you can see all the workings - circuit board, sensor unit, and the spring and tooth wheel.

Mark the position of the spring tensioner/tooth on the MX5 unit - a dab of white nail polish worked for me. This way you will retain the same spring tension. Also mark the position of each of the black wires so you make sure you get the connections right on reassembly.

On each unit, take your phillips head screwdriver and undo the two (outside) screws which hold the AFM wiring connection, but don't pull on it yet. Undo the 3mm allen bolts which hold the sensor mechanisms, and lift them away. Then you can undo the three phillips head screws which hold the circuit board(s) in place.

You can now remove the wiring connection - It will pull out with a little force, but be gentle - the three solders inside each will break off the tabs this is fine - you will repair it upon reassembly. You can now lift out the circuit boards - put each aside separately.

[Uncle Arthur]

You can also lift out the little white plastic temperature sensor - do not lose it, and do not lose the little black plastic spacer ring which will eiter be stuck around the sensor, or to the internal metal of the AFMs or perhaps it will fall loose - either way - make sure you know where it is. You will now also be able to see the spring mechanism on each AFM - it is easy to see (and feel) that the RX7 unit is much heavier.

Undo the 6mm bolt on each - it will feel a little bit tight but will 'crack' with a little gentle force. don't undo it completely - just enough to lift out the U-shaped metal fitting. Now you are free to remove the spring. On the RX7 unit, the spring lifted out pretty easy - others have reported the MX5 one much harder, but I found by gently prising at the black plastic central housing, one side then the other, little by little, I was able to work the spring off the shaft - DO IT GENTLY - you don't want to bend the spring.

Swap the MX5 spring into the RX7 unit - push it onto the shaft - gently, evenly, and slide it home until it seats. Also reinstall the U-shaped metal 'locking bar, and do up the 6mm bolt (which you conveniently left in the housing). Put the temp sensor in place, remembering the black spacer ring, then the circuit board - do up the three phillips head screws. You will have marked the toothed wheel so you know where the tensioner will need to go - put the tensioner in place, and tension up the spring so the marked tooth and tensioner match up. Reinstall the sensor mechanism - to tighten it in place, just do up the allen bolt, but make sure that you adjust the position so the little wire sensor connection aligns with the max/min connections - don't push it too far to the 'far setting' - the little sensor is made up of tiny tiny wires, and if it goes beyond the circuit board, they are easily damaged if you just let the spring bounce back and the wires catch on the edge of the circuit board.

Tighten the allen bolt, and check that the sensor has full travel against spring tension (easiest to do this by pushing on the flapper door), and that the return bar connects with the little switch arm on 'zero' tension, and that the little terminals disconnect - you will see easily how it is supposed to work.

Now it is time to reinstall the connection plug, and resolder the internal connections. I had a mate do this cause I suck at soldering, but the task was made to look pretty easy. Reinstall the two last phillips screws holding the connection plug in place, and then check the flapper/sensor operation one more time - better not to have to pull it all apart again. Last - put the plastic lid back in place - I took the time to clean away all the old silicone, just to make the job look tidy.

If you've done it right, all should be good. The inlet and outlet on the RX7 unit is quite a bit bigger, so you'll need a new silicone joiner to your intake pipe (you may need to fabricate up an adapter), and you'll need to make a new gasket for the other end - rubberised cork from Repco/StupidCheap is perfect - but buy the smallest sheet you can, or go halves with someone - no sense in wastage.

So there you go - reinstall your new hybrid AFM, and rejoice in the additional air flow. You may need to do some tuning/tweaking at idle, but you should see some benefit from better airflow, particularly if you've got an aftermarket intake.

By the way - I'm doing this for my turbo conversion - the piggy back ECU has the corrections for the RX7 AFM's increased flow, and I'll have all the benefits of the factory flapper tension at idle, and better flow across the rev range.

Enjoy

[timk]

This thread is useless without pics!

[Uncle Arthur]

This thread is useless without pics!

I managed to pull them apart, and reinstall without pics, and while doing so, I didn't take any, and I'm not pulling it apart again to take some

Deal

[Boags]

Nice work UA!

[Fatty]

This thread is useless without pics!

nah, it's not. good write up mate. i reckon anyone who has both units in front of them will be able to work it out, even without pics.

[timk]

nah it's not. good write up mate. i reckon anyone who has both units in front of them will be able to work it out, even without pics.

Yeah I agree, just stirring.

[ampz]

That is an awesome write up!
Thanks for your efforts and for sharing this (I will use this soon i think )

You have white nail polish?!!

[adamjp]

Grab the pics from my posts on the RX7 AFM. There really is not that much to illustrate.

http://www.aus-cartalk.com/viewtopic.php?t=24336&highlight=

[Uncle Arthur]

Here'tis.........

[Uncle Arthur]

That is an awesome write up!

You have white nail polish?!!

Yep - g/f was throwing it out - I saw a use for it in the garage.....

Marking the timing mark
Marking alignment marks
Marking timing belt marks (to timing gear).

I could go on

[Boags]

For reference, you can pick up a RX7 AFM from nearly any Mazda Rotary mechanic cheap. They will have installed an ECU in a customer's car and won't need the AFM anymore.

I picked mine up for $20 or $25, I can't remember.

MAKE SURE YOU BUY THE ONE WHICH SAYS \"B\" ON IT. That is the correct one for the application. S4/5 non turbo, IIRC.

Boags

[Boags]

All I know is that the one that says \"B\" on it DOES work...

[mr_rotary]

done this yestartday......the car pulls so much harder now....

btw my AFM is off a 13bt....which have a 'A' written on it...

What's the difference between the turbo and non-turbo AFM's? Is there any difference and which is the best to get for an NA6?

I am now confused as to which one to get!

[Fatty]

i'm guessing that the difference would be the internals - but since you are gutting it and sticking the the mx5 internals in, either should work? that would seem to be the case given that es86 got the tubro one working in his car..