jon88se

I worked on my car for a while today and seemingly fixed the rich idle (few bad vacuum lines, lose intake hose). Anyway, I found an old AFM (I have a few) and decided to play around with it for a bit. You see, after doing a few Turbo conversions on old school 240 z's that use the same flapper door type AFM we had to loosen the spring inside to richen the mixture and fool the "computer." SO...I clean the old one inside and out, contacts and all and put in on the car with a freshly cleaned large K&N conical. I kept the cover off the AFM and made a few runs in and out of my court and in between I tightened the spring a bit to lean out the factory rich mixture. First though, I marked two points to be sure I knew where Mazda had the car set. Leaning out about 8 notches improved throttle response noticeably and gave a nice boost between 6-7 grand not to mention made my idle solid and improving MPG (the car didn't seem to dump gas as much as usual when making a lot of 1st-2nd-3rd gear full throttle runs. BTW, this is for flapper AFM's only...anyone else tuned this way as a cheap alternative to an AFC? I'm just gonna get a decent AF gauge soon and try to get the ratio perfect as I didn't want to lean the car out too much!

Any thoughts?

Aaron Cake

iTrader: (1)

You're leaning out your car without even an AF guage? Have fun rebuilding your engine.

This is a good "cheap" solution to the AFC, but an AFC will give you real control. Remember that all you can do by modifying the AFM is adjust the fuel within the stock system's capability. The "real" solution is to upgrade the fuel system properly.

boostmotorsport

say it again Sam

NZConvertible

This little trick has been around about one day less the flapper-type AFMs have. Obviously it's about the cheapest way to alter mixtures, and can be effective, but it still a very crude method. The main problem is that it makes the same percentage change over the enitire output of the AFM. Anyone who's ever tuned a piggyback fuel contoller or aftermarket ECU on a dyno will tell you it's never that simple. Some areas will need more fuel (usually top-end), others less (mid-range). So if your engine's leaning out up top because of your mods, this method can richen the top end to make it safe, but you may actually lose a bit everywhere else due to rich mixtures. Sounds like you got reasonable results, so it might work better on some cars than others, but is far to crude to be considered a permanent solution to lean mixtures. But hey, nothing like fiddling with something to see what happens!

jon88se

Actually...a couple summers ago when inspection came around I used one o those old AFM's I have and my friend and I leaned it out to run on the inspection dyno and it passed without an airpump We had to lean the car SO much that it wouldn't idle at all no matter how rich the adjustment screw was!! The car drove fine on the dyno though and never pinged or blew (obviously). That was more than like 3 times as much as I leaned the car this time. Also, I don't think the amount I leaned without the AF gauge is unsafe simply because there are those out there that bolt on superchargers to this motor without fuel mods and the car runs fine. I'd expect a low boost form of forced induction at around 5-7 psi to lean the mixture out more than a few notches on the AFM. I went hard on her all day doin this, full load on first, second and third gears - car felt great!! I just got bored, shy of a turbo setup (this summer I hope) I don't have anything left to do to the car

RETed

Bad example...the airflow meter is the primary means of measuring the airflow.&nbsp One good thing about these airflow meter controlled ECU's is that things like supercharging will allow the ECU to add more air up to the point the airflow meter door maxes out and stops moving.&nbsp The added supercharger will work fine on an NA up to the point the airflow meter maxes out...



-Ted

jon88se

Anyone actually think it was harmful?? I had to richen up the idle screw about a turn and a half to get the idle solid after I leaned out the AFM. Considering how far you can actually lean the spring out I don't think 7-8 notches is harmful...isn't the factory mixture overly rich in general anyway? Besides, so far the benefits are great...any ideas besides me gettin an AF gauge?

Aaron Cake

iTrader: (1)

First, AF gauges are not tuning devices. They can tell you if you are ridiculously rich, or stupidly lean. Nothing more. That said, the Autometer is pretty cheap, and seems to work well.

As far as the AFM, I wouldn't mess with it. The factory setting is overall rich, which is quite SAFE. If you start "tuning" the car without the proper equipment, then you will toast the engine. If you really want to do this kind of thing, put in some larger injectors and an S-AFC.

jon88se

yea, i know the AF gauge is not exactly for accuracy but just a tool that will give u an idea of whats goin on in terms of the ratio's at given rpm's. given how many notches u can tighten the wheel, is less than 10 notches really a big deal? if the entire wheel in the AFM has about 80 or so notches then i've leaned out less than 10% i'd say. i'm just askin because of my experience with nissan's this method has worked out really well. also, if i were seriously lean (like the Z's used to be if we over tuned) the car would pop and fire out of the exhaust under deceleration which would always be a bit rough. injectors is way overkill for an NA since the stock injectors shouldn't be operating near 100% duty cycle on the stock motor. An AFC is the real answer but this seems to work harmlessly for now. thoughts? i think this is an interesting topic...

RETed

You're making too many assumptions that are not backed with hard evidence.&nbsp You can't go counting notches and expect them to be a percentage of your adjustment over total max.&nbsp The airflow meter is a LOGRITHMIC type of sensor - the more the airflow, the less a change in the signal output.

I don't recommend anyone messing with the airflow meter.&nbsp It's a really EXPENSIVE piece (from the Mazda dealer), and most people would end up screwing it up; once you kill it, you can't fix it - you'll need to replace it.&nbsp You're correct though...the ECU is programmed in the rich side, so that's why you're seeing gains.&nbsp Run some shitty gas, and I'd bet it'll ping itself to death.&nbsp Add a high mileage motor (over 100k miles), and it'll kill itself in a split second.&nbsp You're taking a huge risk trying something that's putting your engine on the line...

At the very least, run an EGT and tell us what kinda numbers it's putting out...



-Ted

jon88se

would a change in the heat range of the plugs help combat any possible detonation? i'd run high octane but i know low octane is better for the NA cars (right?). what EGT #'s should the car put out? what does ping sound like in a rotary? last question, do the NA's have knock sensors and would it apply in this case in terms of retarding timing to combat detonation. I only ask because the feedback I'm getting makes me wanna assure that what i've done is safe (though it's been 2 days of hard drivin and we're better than ever). about AFM's, i got a whoooooooole buncha them and they all differ - some idle better, some run better. I forgot which this one was out of the four I got but it had the marks on tghe gear inside which means it was the one on the inspection dyno a few years back. I richened it up a LOOOT from the lean point we had it at back then and like i said, the car sputtered and would barely hold an idle. stil passed though on the same motor and with no airpump or anything.

Aaron Cake

iTrader: (1)

Sounds like you're still thinking in terms of piston engines. There really isn't much of a spark plug choice for the rotary...

Ping sounds like...well...uh....a ping....Maybe someone else can explain it better. Note that most likely when you hear the engine pinging, it's already too late and you've blown or damaged a seal. Rotarys do not tolerate detonation.

jon88se

how much have you NA guys with AFC's leaned out your cars and where in the RPM range? any other ideas?

jon88se

I'm gonna take one of the Greddy EGT gauges for myself at the shop...what is the best location to instal the probe and what is a safe range of #'s for an NA with all the usual mods (intake, full exhaust, aluminum flywheel, crank pulley, no emissions).

RETed

The EGT probe should be put closest to the exhaust port, but if you're running the stock exhaust manifold (or headers), this can be a dilemma.&nbsp I'd run it right after the stock exhaust manifold in the "mid pipe" or in the "collector" if you're running headers...

If you do this, shoot for 820C-840C at WOT.



-Ted