before ripping your AFM off your car and following this procedure this is for experienced tuners, i will not be held responsible for anyone blowing their engines due to improper modifications or not following the procedure accurately.

while running into an issue with a customer's car the engine kept stalling out, i noticed the air flow meter black cover was not sealed to the case, i popped the cover off and noticed a few things.. one the clock spring had been tweaked and the car was running severely lean, 2 the solder joints were all broken so i knew someone was dicking with it.

while playing with the clock spring i noticed you can in effect tweak the response of the airflow meter to lean it out or richen up your mixtures throughout the RPM ranges, rather easily in fact. the reason is the door uses the clock spring as a defining factor for how much resistance the flapper door needs to open. this isn't rocket science... if you loosen the spring tension the door moves more freely and the mixtures are richer, tighten the spring and the door has more resistance and take more effort to open meaning leaner mixtures.

the air flow meter is the heart of the fuel injection system on these cars and the meter is very finely calibrated, only a few clicks on the clock spring can have adverse effects on how much fuel the engine gets.

for some vehicles you can bandaid a lack of fuel by richening up the mixture by loosening the clock spring BUT your air flow meter will max out sooner, fortunately the turbo airflow meters max out at about just over 350 wheel horsepower!(factory calibration) the stock cars only used half the sweep of the meter...

1st you need a razor blade to cut the sealant on the black plastic cover then pop it off. before doing a damn thing mark where your lock points to on the gear so you can reverse any screw ups you may do.

so now that you know the basics here is how it works, pictures say a thousand words:



to adjust the spring tension you have to press the lock tab against the housing and use a small pick or screwdriver to rotate the gear. rotate it counterclockwise to richen up the mixture, clockwise to lean it out.


the variable resistor next to the pressure sensor on the RF strut tower can be used to somewhat lean out a fatter mixture when the engine is in 'idle mode'.

this is only recommended for those who have widebands on turbo cars, n/a cars likely don't need any AFM tuning unless you are leaning it out a tad for better economy, no wideband is necessary in that case. turbo car owners watch your wideband and be sure you didn't accidentally lean out the clock spring instead of richen it up.

for Rtek users this will also allow you to tighten the spring tension to actually run the car over 400whp and still have air flow meter feedback. you will need to fatten out your maps all across the board however.

once you're done and satisfied, apply some RTV to the black cover and reinstall it.

at the bottom of the first picture is the arm that opens the fuel pump circuit to shut off the pump, this is why cars with vacuum leaks have stalling issues. you can modify the arm or remove it to essentially keep the pump from ever turning off if the AFM closes too far, but your pump will always run with the key to on.

never seen anyone delve into modifying these air flow meters so here you go..

 

This is very interesting. I don't have a wideband so can't try it myself but am intrigued to see how much of a difference it makes in the a/f ratio per click or two of the clock spring.

 

Yea I was going to do this for a year. about time someone posted an s4 Na mod. nice

 

Hmm!
I am wondering if this would be beneficial to Guys looking to pass an Emissions test.
Can you comment on this Ben?thanks.

 

quite possibly but only for some reason like say you are running 720 injectors and only as a temporary adjustment. minor AFR changes can in fact be done with the variable resistor, anything beyond its range could be modified with the AFM.

consider this as a non linear tweak, towards the end of the door's travel the less the clock spring adjustment has an effect. so it does have a much more noticable impact on lower RPM fuelling but it will make changes throughout the engine's RPM range.

 

Considering the emissions test in nz is a/f ratio based I assume yes it may help but we are only required to do an emissions test when certifying major modifications and it's at the certifies discretion whether he even tests it at all. I find this odd as being pre 1990 I'm not even required to run cats.

Though you probably weren't asking me if rotaryevolutions name is ben also.

 

It would be on an N/A anyways.I am getting a beater,and of course,it is an 88 which needs Emissions testing.(price is good,so I couldn't pass it up!)
I got fed up with the Electronics of the Stock setup and went stand-alone on the turbo car.

 

Theres no fine tuning for the S5 afm is there?

 

Sounds like a great way to tweak your AFR's on a car that is almost passing a sniffer test.

On a side note, spec racing classes dyno tune their AFM's like this so there's definitely some benefit. It can also cause a 1.6 miata to start detonating when you tune it on a 78 degree day then run it at 3am in December. So like a lot of other things, you're trading a factor of safety for more power.

 

its kind of an old school last resort kind of thing. there are actually several adjustments that can be done, there is the spring, and there is an air bypass for low engine speeds.

my gsl-se also had a stopper bolt on its AFM, so it controlled how far the door opened, makes it really easy to change the WOT mixture.

i've never tried it, but it looks like you can adjust the relationship of the flapper door to the electrical wiper too.

i've also seen some really wacky stuff like this


where the guy has replaced the resistor board with potentiometers, so the AFM is fully tunable, although i guess he'd never heard of an SAFC.

 

For those of us who won't bother with an SAFC off ebay...

 

even used SAFC cost over a hundred bucks, for non turbo applications who are trying to save a few bucks in gas the SAFC is counter intuitive. i also always see people asking about bandaids for higher boost, this is one that is free.

i agree though, for any real modifications a way to accurately tune fuel is needed. i just found it interesting messing around with the guts inside the airflow meter.

this gives people an idea of what to expect with the cover removed, in some cases i find the fuel pump connectors bad and this also allows you to clean the connections and physically see if the AFM is bypassing air to close the switch or if the switch itself is faulty.

the idle air bleed screw also gives a way to lean out the low RPM mixtures to compensate for loosening the spring tension on the clock spring. you need to drill out the tapped in cover that covers it though. with the variable resistor idle can easily be right where you want it while richening up the higher RPM fuelling.

 

I could've sworn I saw a thread on this whole thing a long time ago... But anyways, an invisible penny for your thoughts:

What do you suppose the benefits would be in richening up the AFM setting on an N/A car that has better-than-stock breathing? (e.g. bigger ports, different intake, modified throttle body, etc...)

And with a wide band, what would I want to shoot for? Being N/A and all, should I just go for 14.7:1? Or richer? Let's pretend this is just for performance, no MPG or emissions taken into account.

Thanks.

 

I opened up my spare afm to see how easy this was, noticed any adjustment for richer mixture results in the door not shutting?

 

performance? power will be between 12.8 and 13.8. part throttle cruise, as lean as you can while at the least amount of nessasary throttle. you'll find richer than 14.7 for cruise makes you use the lowest amount of thottle.

 

so adjusting the spring tension has no effect to the fuel mix while in the "idle mode"?
ps, what's the RPM transition point away from the "idle mode" on the S4 TII?

i ask these questions because soon I'll be running the Rtek7 v2.1 w/750cc primary vice the suggested 720cc and concerned over the idle fuel mix. hopefully I can get the proper mix via both the variable resistor and the AFM's bypass air adjusment even with fuel psi set to ~40.

 

below 1k RPMs the engine will use 0 timing(stock 5/20 ATDC timing) and will base the fuel mixture off the AFM and the variable resistor. reclocking the AFM will still result in a richer misxture but you can use the air bypass screw on the AFM to tweak the low speed AFR as well as the variable resistor to lean out the idle below the 1k transition point.

 

idle seems to be anything under 1024 rpm, and about 5 degrees of throttle.

the ecu seems to have an idle map, and of course the variable resistor.

edit; what he said ^^^^

 

I ran into a similar thread on another forum while searching and trying to get better mpg's out of my daily driver 90 4runner.those trucks from factory are tuned richer at the vafm so I leaned it out a few clicks(3 clicks)and received an extra 35 miles per tank,truck has better acceleration and runs a lot smoother.

Now wondering if I should mess with the one in my rx2(12a turbo running 13b stock injection) to see if it would run any better.

 

Rotary Evolution:

I appreciate your take on this subject as I have been researching it for quite some time. Seeing as you are a respected forum vendor and member, do you have any insight as to how many adjustment clicks are necessary? It seems to me that this would be dependent on the car and what mods have been made?

In my case I have a 88 GXL with quite a few mods, (no port though) and I run pig rich. I adjusted the AFM two clicks clockwise. Immediately, I noticed smoother acceleration and a few extra MPG's. Unfortunately, I do not own a wide band, which would of been the proper way to measure the changes.

That being said, any adjustment tips based on modifications to the car itself (I.E. max adjustments)?


Woooo... sorry for the long post!

 

the only true way to know for sure would be with a wideband unfortunately. but if mileage is up and the car seems happy with an n/a that is all you usually need. you can go too far but the engine will usually tell you if you're being too aggressive with leaning it out.

i have tuned numerous n/a engines without any gauges, lean out the mixture until the idle begins to hunt or while cruising/accelerating it begins to hesitate. once you feel a hesitation you now know where it is borderline too lean and you can add in a few clicks to richen it back up. turbo engines simply require a wideband, you can't guess or tune by feel with a turbocharged engine because it will seem happy all the way up until the engine lets go.

 

Thanks for the response. I figured this was the case with the na motors. With my two click adjustment, the only thing hurting is my cold start-up idle. Probably doesn't help that all my emissions and bac were previously removed :p

 

you can also compensate for idle quality with the air bypass screw, which is hidden under the blind cap which has to be drilled out. if this screw is backed out too much though to lean out the mixture aggresssively it will cause the fuel pump switch to work erratically(it can be bypassed though) and cause stalling issues while cranking. turning the screw clockwise will richen up the mixture and not affect the pump switch.

make a note of how many screws it takes to bottom out the screw before making any actual adjustments.

 

Hmm. I have adjusted both the air adjust and the variable resistor( using the FSM jumper method) in addition to leaning out the AFM. With this in mind, my idle is now perfect once warmed up. Yet, cold start up is still terrible. In order to stop the car from stalling, I need to keep the rpms up for about 2-3 min to warm it up. Any thoughts? (I have verified no vacuum leaks)

Edit: Reinstall BAC that was removed by previous owner?

 

Adjust thermowax and definitely reinstall the BAC (removing that was stoopid).