AFM modifications revisited... UPDATE/PICS
 

I had planned to do this months ago as some of you will remember. Well, I finally got around to doing it, and here's a brief report as I promised (I would think that this could be applied to the turbo, but the boost curve as another factor to worry about, and me not having any hands on experience on those cars, I will not comment, yet):

OK, the idea is to increase throttle response, and air flow specially at part throttle-low end/midrange. Basically, drill holes in the flap (reducing the flap's mass, and restriction). But to counteract the reduced restriction, the spring tension needs to be backed off (so that the flap opens at nearly the same angle even though there's not as much air pushing on the surface of the flap), which also reduces 'lag', improving throttle response.

Basically, remove, drill, re-attach, and calibrate. For the last step, I used an air/fuel gauge, and a tachometer, ofcourse your ears are another valuable source of input...

http://www.pelicanparts.com/ultimate...irflowmod1.jpg http://www.pelicanparts.com/ultimate...irflowmod2.jpg

http://www.pelicanparts.com/ultimate...irflowmod3.jpg http://www.pelicanparts.com/ultimate...irflowmod4.jpg

http://www.pelicanparts.com/ultimate...irflowmod5.jpg http://www.pelicanparts.com/ultimate...irflowmod6.jpg

I could back off exactly 19 teeth off the spring adjuster on my car, not to mention all the holes that air can now flow through. Throttle response seems improved, and at least in neutral, the mixture can be adjusted right (though it took me about two hours to get it just right). I did my measurements at idle, 2k rpm, 2300rpm, 2500rpm, 2700rpm, 3krpm, and 3200rpm. After re-indexing the flap/potentiometer (the device that's affixed to the top of the flap, that generates the actual electrical signal), everything seems to work fine.

As you know I can't legally drive on the street, but in my driveway the car seems a good bit more responsive, specially of idle, and during transition from part throttle to full throttle. For a grand total investment of (tada) $0, doesn't seem too bad.

If I have time later, I'll tackle some custom DME work, but I'm not sure the returns will be worth it. I'm planning to sell this car, and pick up a 951 as well as a possible other new/new-ish car right now so don't expect anything else too soon.

The only thing to watch for is taking the bolts off that hold the AFM against the airbox (one of them is in a tight spot, I had to 'customize' a cheap no-name bit "driver", second to last picture shows this tool), and to not get any aluminum shavings into the AFM.

PS: I did a write up of this, and the DME mod a couple of months ago for my computer app. project, more info is at my website.

Please reply here instead of e-mails, concerning this and/or the DME mod(s).
Ahmet
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It's all the driver...
My page over1g@hotmail.com
Porsche owners Gallery.../My 944

[This message has been edited by 1.2gees (edited 06-26-2001).]

When I first came up with the idea I wouldn't stop receiving e-mail, and there were numerous replies to the tread, and now when it's completed, not one? Funny...
Ahmet

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It's all the driver...
My page over1g@hotmail.com
Porsche owners Gallery.../My 944

[QUOTE]Originally posted by 1.2gees:
Hi Ahmet, hey that project sounds like an interesting Idea, now is there anyone that can drive the car in stop and go traffic to see what your results are, I too am bothered by the anemic off the line engine response and I am not interested in having to rev it and drop the clutch to make things happen, the only thing now is that I have a 951, now someone else might say that they would think a MAF might do the trick but I dont have 1200.bux to blow on this either, so I think more research is in order.
I hope it works for you.............Stan

I could back off exactly 19 teeth off the spring adjuster ...

you should have just back it off 2 teeth(counterclockwise) and not drill it...this i have done on my previous car(not a porsche)...just don't want to respond on your previous post(due to no dyno sheet to prove)(everybody wants it to know if it can be proven)...basically backing it off(loosening the tension) will put you on a richer side..loosening it richens it(now this where the ignition come on)..
just my 0.02 cents..

Ahmet, congrats on finally going through with it ... I hope you find good results when driving on the street ...

My question that has never been answered by anyone on this board is .... What MPG readings do you get at the various rpms you calibrated your MAF with ...

My idea is that I want to compare my readings to other peoples', so I will find out if my low MPG average is due to running rich or not. I tried the signal from the O2 sensor, and it gave me normal readings that oscillated between .3 and .7 when driving normally ... but I'm getting like 15 MPG ... which sucks when comparing with all the other 944na owners, who allegedly get at least 23 to 30 MPG ...

I would really love to solve this problem, so I want to know if tuning the MAF will help or not ... my only worry is making it too lean ..

thanks.
Ehab

Stan, I may look into the same mod for the 951 but not before I get one... If anybody's interested in doing something similar to this on a turbo, I can work with them no-prob.

porscheboi928s/c944t/n, because of the reduced surface area of the barn door, backing off 19 teeth was the ticket for me, one less or more and the car wouldn't run right. The spring still has good pressure, just nowhere near what it had before, much less restriction. The mixture indeed is correct so far, at various rpm/idle. Details are at the web site/my original post.

Ehab, at idle it should be around 45hours/gallon(?), but the gauge is not what I would go by. An exaust gas analyzer to set the mixture right would be where I'd start. Are you sure it's not just you driving a little fast? I can get down to 8mpg (on track), and up to about 36+mpg (on the highway going steady ~70mph). Clearly driver makes most the difference. PS: 100%full throttle is a lot LESS economical than 99% throttle, as at full throttle the engine is run much richer compared to any other throttle position.
Ahmet

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It's all the driver...
My page over1g@hotmail.com
Porsche owners Gallery.../My 944

i have a question, and perhaps others are wondering: if this mod really works and improves response to a significant degree, why wouldn't have porsche designed it so?

i mean, a single veteran porsche factory mechanic knows more than we do put together.

http://home.pacbell.net/nirky/turbo_120.jpg

Well, I was talking to somebody today about why the 924 was such a good car, and I came out with, cause it's fun to drive. The 944 does handle better, look better (IMO), has better brakes, but is it more fun to drive? I think so, but not by a great margin. Now if the car didn't weigh any more, but had about 20 more hp, it'd be a lot more fun wouldn't it? (Like the european 944s), now it didn't have those 20 ponies, that would've been easy to get, no? Well my 944 passes emissions without a cat, so it definately wasn't that.

Could it be because they didn't need to? I don't know. Why didn't the 944 turbo come with 50 more hp? The rest of the chasis would be just fine with a little more boost, I think you'll agree with me there...

Anyway, I think this works fine for me (but haven't driven the car on the street, it's tempting, we shall see), try at your own risk, and keep in mind tuning was a b*tch.
Ahmet

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It's all the driver...
My page over1g@hotmail.com
Porsche owners Gallery.../My 944

Well, I drove the car to the gas station:

Max acceleration is improved slightly, however throttle response is NOT improved drastically, like I'd expect.

If I were to do this over, I'd drill about half the holes I drilled this time, backing off the spring tension by a little bit, but not as much as I did. Maybe I'll try covering SOME of the holes with tape, and re-indexing the spring tension, if so I'll post updates.
Ahmet

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It's all the driver...
My page over1g@hotmail.com
Porsche owners Gallery.../My 944

Ahmet
I did something similar to my 735i....it looks as if it has the exact same AFM! All i did though was back the spring tension off by about 3-5 notches....from my understanding -- the AFM really controls idle more than WOT....the one thing i did notice was the "needle" had wore a groove in the resister panel, right around where the needle would be at idle -- or just off idle(on throttle)....interesting....i think a new AFM would do wonders on either car. You have to factor in 15 years or so of driving on that seemingly delicate piece...just some thoughts...

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Ahmet just outta curiousity, what way is it on the dial to back off on the spring tension? is it to turn it clockwise or counterclockwise?

http://eurospecporsche944.homestead.com/files/sig.jpg

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Porsche. Es gibt keinen Ersatz.

Clockwise.

Are you sure it is clockwise to REDUCE tension???? It seems to me that it is the other way around, and since I'm trying to get better gas milage, I turned mine clockwise a few teesth to increase the tension!!! Could you double check Ahmet!!!

Thanks.

Well counterclockwise WILL decrease the tension, but to make the car run leaner (if you're not doing any other mods) you'll wanna turn the dial clockwise.

Because with less tension, the same amount of airflow will open the flap more, calling in for more fuel, the only way to lean the mixture out without drilling holes (on the AFM) is to turn the thing clockwise, but I would advise against this. Without holes, only about 1 click is acceptable, as anything more puts the air/fuel out of whack.
Ahmet

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It's all the driver...
My page over1g@hotmail.com
Porsche owners Gallery.../My 944

Well, when I took the car to be 'tuned', the mechanic found that the previous owner had messed with the AFM and truned it 8 TURNS in the wrong direction to make it run rich, and that is when my exhaust was black and I got about 8MPG all the time. He said he fixed it, and used his diagnostic tools to figure out the right A/F mixture. However, I have fixed many things since then (back in April of 2000), like cleaning my throttle and my vacuum lines and AAV etc. etc. ... So to improve my milage, I wanted to lean out my mixture further. I turned it about 4 teeth clockwise yesterday, and didn't notice any changes in idle or revving rpms or power, so I think i need to go even further. I don't see how one tooth is giving you such drastic resluts.

Another interpretation is that my AFM could be still way too loose for a few teeth to make a big difference, all the more reason for me to tighten it up even further.

What do you think???

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Lock Stock '84 944 and two smokin' tires ...

I'd lean it out from the DME, tightenning could give you better low end I suppose, but doubt better economy.

On mine ONE click makes a semi-significant change, and three clicks made a really big difference... Maybe your AFM is not functioning the way it should (not saying that for sure). If you have at least an air/fuel gauge, I would do further testing, also look at the spark plugs. You don't want to run the car too lean, but it should be OK with a bit leaner than stock. Let me know of any further questions, and keep me updated.
Ahmet


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It's all the driver...
My page over1g@hotmail.com
Porsche owners Gallery.../My 944

Well, I don't have a A/F meter, but I have easy access to my newly installed O2 sensor signal with a digital voltmeter. What readings are acceptable as 'within stock setting' ... the last time i monitored the O2 sensor signal, it would oscillate between .3 and .7 to .8 volts depending on the throttle position, the more open, the richer the mixture. I also keep an eye on the MPG meter, since it is a direct indicator of how much fuel is being injected, which is very strongly affected by the signal from the MAF, right?

so for the same circumstances, i would expect that the MPG meter would read higher values (better economy) if I tighten the MAF, right?

I think the reading's supposed to be around .6 or so, but am not positive off-hand.

The reading should NOT move around too much when under steady load. The car will run VERY lean when backed off the throttle (infact, 0 fuel is being injected, while rpms drop at 0 load), so if that's what you're implying then all is good. MPG meter will give you a good idea, and it's very precise, but not accurate at all.

The mpg meter is NOT affected by the AFM signal, once the flap is all the way open (this happens around 2700rpm at full load), only throttle position, and crank angle/speed matter after that point. If you make the car run lean through the spring tension alone (and without drilling holes), you may loose a bit of power. I'd seriously look into adjusting the setting at DME.

I'm quite certain that the tighter you make the AFM, the better economy the gauge will show, but the less power you'll make (which may force to apply more gas, loosing economy). Driving technique makes all the difference.

Anyway, have you messed with the DME? If not, 3%leaner with 0 timing change could be the ticket for ya. Let me know what you think.
Ahmet

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It's all the driver...
My page over1g@hotmail.com
Porsche owners Gallery.../My 944

OK, voltage from oxy. sensor is supposed to be between .7 and .3 volts.

.45volts is usually considered corresponding voltage output from a normal functioning oxygen sensor, when the mixture is exactly 14.7parts air to 1 part fuel.

I would not go below ~.35 volts on the 944 (the lower the voltage, the leaner the car's running). At full throttle, it's OK to have a reading that's overly rich, and it's also OK to have a reading that VERY lean, after backing off the throttle, while the rpm is dropping. (Both are also normal)
Hope this helps, let me know.
Ahmet

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It's all the driver...
My page over1g@hotmail.com
Porsche owners Gallery.../My 944

Thanks Ahmet, I actually took out to DME the other day, and made sure it is set to the stock settings. My goal is not to modify anything out of the stock settings, rather, I want to have the stock setting on my AFM, which I belive has been messed with plenty in the past by the previous owner. As a result, I would like to get the fuel economy the most people on this board are reporting (at least 20 MPG in town, above 25 highway).

I will let you know what happens.
Thanks for the input ...

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Lock Stock '84 944 and two smokin' tires ...