3.2L Air Flow Meter calibration research prodject

[scarceller]

I have looked for procedure on howto adjust calibrate the Air Flow Meter (AFR) on a 3.2L 911 Carrera and have had little luck. This is the Barn Door AFR. I'm looking to collect some data from anyone who wishes to help, if you have a 3.2L with a NEW or properly working AFR I would like your help in gathering some numbers. The testing is not very hard and requires removing nothing from your car.

Heres what I'm looking for: Pull back the rubber boot on the plug that goes to the AFR. then from left to right you will see 4 wires the far left and far right are for temp sensor in the AFR we won't look at these. The 2 center wires are the 5Volt supply line to the sensor and the other is the output of the barn door sensor at idle the output is somewhere around 1Volt to 1.3Volts.

What I need:
All tests are with the car running and parked.
1. Use multimeter black lead to ground then find the 5V wire and record the voltage should be 5V +-.2
2. At idle tell me your idle speed (850RPM or so) and tell me the voltage on the send line (should be about 1Volt)
3. Have someone bring the RPM to 1000RPM record the voltage
4. Now bring RPM to 2000RPM record the votage
5. Next, RPM to 3000RPM and record the voltage.

I wish to come up with a baseline of how these Barn Door AFRs work. Let me know a little history of the AFR as well as the car.

Once I collect the data I will try to determine results and the end result will be an adjustment procedure document with all the numbers provided. If I get enough numbers say 20 or so I think I can come up with some solid observations.

I have seen several posts on adjusting the black wheel within these sensors a click or 2 to the right or left. But after spending much time anyalizing my sensor I'm not so sure this is the best way to adjust these sensors. I am working on a much better adjustment procedure that calibrates these sensors at Idle 1000,2000 and 3000 RPM
and then sets the base voltage by adjusting the pointer to achieve Lambda (AirFuelRation 14/1). I believe that messing with the spring tension and ignoring it's effects at higher idle is just a bad idea.

I promise to try to come up with a procedure to be used by all for verifiying and calibrating these sensors.

If you wish to help but need more info or just aren't sure how to get the readings please contact me at sal.carceller@cox.net

In Summary, heres a quick list of what's needed:
1. Supply Voltage to the AFR at idle (5volts)
2. Signal Voltage at idle (850RPM)
3. Signal Voltage at 1000RPM
4. Signal Voltage at 2000RPM
5. Signal Voltage at 3000RPM

[scarceller]

I started this thread many months ago but since then I have learned a lot about the Air Flow Meter in our 3.2L Carrera cars.

Get all the details on just how this device works and why you really should not try to adjust it unless you really fully understand it. Or of course if you have an old one you don't care about, go for it.

I have spent many hours on this project over the past year and have summurized all that I have learned into a single dowloadable word document. If you ever intend to adjust/calibrate or have done so in the past you may find this worth reading:

http://members.cox.net/widebody/AFM/AFM3.2LCalibration.doc

[not sharp]

WOW! Great info, appreciate the effort and strong report.

[ghnat]

Wow, and no replies. I just downloaded the doc and will take a look. I do not know enough to comment on the work, but I will use it in the future. Thanks for the hard work.

ps. Just as I replied there was a post...

[burgermeister]

Boy you spent some time on this one. Thanks!

[rcaradimos]

Found this on the web... don't know if it helps

http://www.autospeed.com/cms/A_0217/printArticle.html


Issue: 34 Section: Technical Features 15 June, 1999
Cheaply Monitoring Air/Fuel Ratios
Building your own LED Mixture Meter
By Julian Edgar
Click on pics to view larger images
Advertisement

Advertisement






One of the most difficult aspects of modifying an EFI or engine managed car on a small budget is knowing what air/fuel ratios are occurring at different combinations of loads and revs. The ignition timing maps won't usually need much tweaking for a budget car to run well, but more power needs more fuel, and knowing how much extra fuel to add can be quite tricky. However, there is an easy and cheap way of getting a rough idea of the air/fuel ratios being used. It is certainly not a technique accurate enough to guide you when mapping programmable management, or to use when modifying a mega-dollar engine, but it is far better than tuning by "feel" alone. It is also much cheaper than having professional exhaust gas analysis carried out on a chassis dyno every time you make a tuning change.

[MMiller]

Originally Posted by scarceller

I started this thread many months ago but since then I have learned a lot about the Air Flow Meter in our 3.2L Carrera cars.

Get all the details on just how this device works and why you really should not try to adjust it unless you really fully understand it. Or of course if you have an old one you don't care about, go for it.

I have spent many hours on this project over the past year and have summurized all that I have learned into a single dowloadable word document. If you ever intend to adjust/calibrate or have done so in the past you may find this worth reading:

http://members.cox.net/widebody/AFM/AFM3.2LCalibration.doc

Sal...any chance your info is still available? The link above seems to be no longer active..

regards,

[stlrj]

Sal,

I think you're going down the right path since most of the 3.2 performance seems to be locked up inside that mysterious AFM.

I found that out when I recently replaced my AFM on my 87 3.2 from one I picked up from the Parts Heaven swapmeet. It cam out of a 964, but when I plugged it into my 3.2, it made all the difference in the world. Smooth idle, tons of low end torque with plenty of top end zoom, clean exhaust (no smell) and great gas mileage like 25mpg in town and near 30mpgs highway.

I get the feeling that Bosch has continued improving the AFM algorithms with the arrival of the newer 911s that would also benefit the older 3.2s. I also opened up this new 964 AFM to see if I could improve upon it with slight adjustments to the spring tension and pointer position etc, but found there was nothing I could do to make it any better than the original settings.

I hope you could find a later AFM from a 964 or 993 to verify my results and reap the benefits.


Cheers,

Joe
87 Carrera

[MMiller]

Originally Posted by stlrj

Sal,

I think you're going down the right path since most of the 3.2 performance seems to be locked up inside that mysterious AFM.

I found that out when I recently replace my AFM on my 87 3.2 from one I picked up from the Parts Heaven swapmeet. It cam out of a 964, but when I plugged it into my 3.2, it made all the difference in the world. Smooth idle, tons of low end torque with plenty of top end zoom, clean exhaust (no smell) and great gas mileage like 25mpg in town and near 30mpgs highway.

I get the feeling that Bosch has continued improving the AFM algorithms with the arrival of the newer 911s that would also benefit the older 3.2s. I also opened up this new 964 AFM to see if I could improve upon it with slight adjustments to the spring tension and pointer position etc, but found there was nothing I could do to make it any better than the original settings.

I hope you could find a later AFM from a 964 or 993 to verify my results and reap the benefits.


Cheers,

Joe
87 Carrera

Joe, was the 964 unit a simple plug and play on your 3.2? Or were modifications mounting, wiring or other come in to play?

regards,

[scarceller]

Originally Posted by Panerai

Sal...any chance your info is still available? The link above seems to be no longer active..

regards,

Mike,
PM me with an email addr for you and I'll send the doc.
Bottom line is the AFM is a very precisely calibrated device and you should never mess with the spring tension on it! I explain what happens if you do in the doc.

[scarceller]

I never tried a 964 AFM in the 3.2L but my bet is that AFM has a different AirFlow to Voltage curve and won't properly match the 3.2L. The 964 is larger displacement engine and the end result would likely be a lean running 3.2L. I'm not 100%, it's just a educated guess. The only way to know for sure is to put them both on a flow bench and record voltages for given flow rates. Or you could sanity check them in car by spinning engine up to 4000RPMs and taking voltage readings of the AFM output for both units. I'm guessing the 964 unit will read lower voltage.

[stlrj]

Originally Posted by scarceller

I never tried a 964 AFM in the 3.2L but my bet is that AFM has a different AirFlow to Voltage curve and won't properly match the 3.2L. The 964 is larger displacement engine and the end result would likely be a lean running 3.2L. I'm not 100%, it's just a educated guess. The only way to know for sure is to put them both on a flow bench and record voltages for given flow rates. Or you could sanity check them in car by spinning engine up to 4000RPMs and taking voltage readings of the AFM output for both units. I'm guessing the 964 unit will read lower voltage.

I'm betting you're right. As lean as it must be, my engine seems to run a bit cooler than before and it appears to like the new AFM.

Originally Posted by Panerai

Joe, was the 964 unit a simple plug and play on your 3.2? Or were modifications mounting, wiring or other come in to play?

regards,

I did a parts search recently and it pointed that all the AFMs from 84 up to the 964's were interchangeable. However, since the 964 AFM mounts upside down, I recall having to flip a bracket over...not a big deal.

[Tippy]

I had a 964 unit on mine. AFR's seemed normal but a tampered a lot with the air bypass screw. Then, I decided to wire 9-volt battery in the wrong pins and smoked all the resistors......doh

[stlrj]

AFM tweekers are truly a very rare breed here or in any other forum, me thinks!

[al lkosmal]

Originally Posted by Panerai

Sal...any chance your info is still available? The link above seems to be no longer active..

regards,

Any chance that I can get a copy of this doc? I have a project that could benefit from this info.

regards,
al

[mikedsilva]

Originally Posted by al lkosmal

Any chance that I can get a copy of this doc? I have a project that could benefit from this info.

regards,
al

Is this document by Sal still available? Would love a copy if possible.
Mike

[Sabai]

pm sent for a copy of the doc

[ant7]

Could I get a copy too ?
Regards,Ant.

Originally Posted by Sabai

pm sent for a copy of the doc

[burgermeister]

Been almost a decade ....

Sal does make a very nice MAF conversion kit that eliminates the flapper box completely. I can attest that my car has never run better.

[LBEEMING]

Has anyone actually got some idle values for their AFM?

After adjusting mine to "stock" positions, I am reading ~1.3V at idle (850 rpm) engine fully warmed.

Interested to see if anyone else has given this a go? Seems Sal was pointing to 1V however I'd have to probably start changing AFM spring position to achieve that.