Fuel Air Mixture

[qikqbn]

Before you go with the vacuum switch, what is your MAF signal right now at idle. It should be around 15.5 kg/h. If not put around a 560 ohm resistor inline on wire #5. Check the idle MAF signal again. Add or subtract resistance as required to get it to 15.5. Once completed, I suspect your WOT A/F ratio will be pretty close to what you are looking for. The variable MAF control is what I use because I also have a variable intake system which increases intake air at higher rpms. In your case, since all your air is going through a constant sized intake, a single resistor will work. If your A/F ratio is a little high or low at WOT, either increase the resistor size slightly to make it more lean or decrease it to make it richer.

If, for some reason, your ECU was tuned incorrectly, the variable MAF control may be the answer. Using the vacuum switch as I described will provide a seemless, instant transision between signals. Set the switch to be off with ANY vacuum and on without.

No way.... so since I am running a straight 3 inch Maf housing and intake pipe all the way to the throttle body a single resistor or rheostat would

have done the trick??

so are you saying all I had to do was add a little resistor inline on my maf signal to the ecu similar to like this photo??

http://www.houseofrage.com/tundra/rrtun33.jpg

Or run a single rheostat inline before the ecu and just dial the rheostat down to get the desired 15.5 kg/h reading at idle??

That makes a lot of sense since the smaller 3 inch maf housing piping has globally offset the the voltage. just turning down

the voltage globally to the levels that a 3.5 inch housing would produce would be enough to trick the ecu. ****, your good.

wow, should have had this dialogue a week ago. I would have loved to try this out, but at this point I have already committed

to, installed and dialed in the AFC-SELECT unit... I am still very pleased with the results I have and the fine tuning flexibility the AFC-select +/- 50%

correction it gives you makes it a really fine tuning gadget. Plus it has a lot of cool flashing lights... haha...

One last question... so is an AFR of 13 flat across the board the most ideal setting or is 12-12.5 a better bet???

Thanks so much for your input. I learned a lot! I am sure this dialogue will help a lot of members.

Bill

[1999Porsche911]

Before you go with the vacuum switch, what is your MAF signal right now at idle. It should be around 15.5 kg/h. If not put around a 560 ohm resistor inline on wire #5. Check the idle MAF signal again. Add or subtract resistance as required to get it to 15.5. Once completed, I suspect your WOT A/F ratio will be pretty close to what you are looking for. The variable MAF control is what I use because I also have a variable intake system which increases intake air at higher rpms. In your case, since all your air is going through a constant sized intake, a single resistor will work. If your A/F ratio is a little high or low at WOT, either increase the resistor size slightly to make it more lean or decrease it to make it richer.

If, for some reason, your ECU was tuned incorrectly, the variable MAF control may be the answer. Using the vacuum switch as I described will provide a seemless, instant transision between signals. Set the switch to be off with ANY vacuum and on without.

No way.... so since I am running a straight 3 inch Maf housing and intake pipe all the way to the throttle body a single resistor or rheostat would

have done the trick??

so are you saying all I had to do was add a little resistor inline on my maf signal to the ecu similar to like this photo??

http://www.houseofrage.com/tundra/rrtun33.jpg

Or run a single rheostat inline before the ecu and just dial the rheostat down to get the desired 15.5 kg/h reading at idle??

That makes a lot of sense since the smaller 3 inch maf housing piping has globally offset the the voltage. just turning down

the voltage globally to the levels that a 3.5 inch housing would produce would be enough to trick the ecu. ****, your good.

wow, should have had this dialogue a week ago. I would have loved to try this out, but at this point I have already committed

to, installed and dialed in the AFC-SELECT unit... I am still very pleased with the results I have and the fine tuning flexibility the AFC-select +/- 50%

correction it gives you makes it a really fine tuning gadget. Plus it has a lot of cool flashing lights... haha...

One last question... so is an AFR of 13 flat across the board the most ideal setting or is 12-12.5 a better bet???

Thanks so much for your input. I learned a lot! I am sure this dialogue will help a lot of members.

Bill

Changing the size of your plumbing and the flow of air past the MAF accomplished the same thing a 5 cent resistor does, only with alot more work. All each acomplishes is to reduce the output signal of the MAF to coincide with the maps of the computer. An A/F ratio of around 12.5 would work well. Look at your after cat O2 sensors while at WOT near redline and make sure that they read 0.88 - 0.90 volts and chances are, your A/F is pretty close to that. Higher numbers would be richer and lower would mean leaner.

[tholyoak]

Right around 340 ohm works well for a stock 996 program using a stock boxster maf housing. I would put in a variable pot resistor, this will allow you to 'tune' the fuel trims right where you want them. 1999 explained this to me a few years ago when I did my first 3.4 conversion. I still think the best solution is to use a properly sized intake tract, as I'm not convinced that the small boxster intake system can flow enough air to feed the 3.4. Look how porsche increase the airbox size when they put the 3.4 into the 987 vs the 986.

-Todd

[Porsche_Monkey_4life]

Where exactly does the resistor go? Anyone have a write up on this?

[1999Porsche911]

Where exactly does the resistor go? Anyone have a write up on this?

Cut the MAF cable white wire (pin #5) and splice back together with the resister inline.

[qikqbn]

Right around 340 ohm works well for a stock 996 program using a stock boxster maf housing. I would put in a variable pot resistor, this will allow you to 'tune' the fuel trims right where you want them. 1999 explained this to me a few years ago when I did my first 3.4 conversion. I still think the best solution is to use a properly sized intake tract, as I'm not convinced that the small boxster intake system can flow enough air to feed the 3.4. Look how porsche increase the airbox size when they put the 3.4 into the 987 vs the 986.

-Todd

I wanted to give a quick update on my current setup as of last night ...

After 7 months of running a "calibrated" maf signal

I finally decided to track down the proper MAF housing size and got my hands

on Todd's recommended "Cayman/Boxster 987" Maf housing . Brand new from

Sunset Porsche parts the discount is still a lot ... $275 because it includes

the actuall sensor which I can not use.

All I wanted was the housing tube to plug my boxster/996 sensor into. I finally tracked

down the proper size maf housing from a dismantler and saved myself

over $200...It also has the screen built into it to help with air turbulence.

In the process I also discovered a proper sized nice alternative

Bosch maf housing for a lot less $$ then Porsche... (pm me if interested)

My original 986 boxster maf housing measures inner diameter of 70-72mm.

(76mm or 3 inch outer diameter)

The 3.4 liter 996/Cayman maf housing measures inner diameter of 83-85 mm

(90mm outer or 3.5 inch outer diameter)

A difference of close to 20 percent in size.

With my "calibrated" maf signal my air fuel ratios were staying a solid 12-12.5 and the car was running very strong.

Even so I still felt that "tricking" the ECU with a calibrated signal or resistor may not be taking full advantage

of all the fuel maps and how they were designed to work with proper air flow measurement from Porsche.

Even though I really enjoyed my setup there was always a question in my mind if I

was really allowing the programming to work correctly under those "calibrated" conditions.

Since I want my 3.4 Boxster to run it's strongest at all times I decided it was time to

switch over to the proper maf housing size.

After modifying intake tube lengths for the new housing I got

it to fit nicely.

My current intake setup is:

-Cone filter plugs onto front end of Cayman Maf Housing..

-back end of housing plugs onto 3 inch intake tubing all the way to Throttle body.

(996 throttle body is only 3 inches in diameter)

I unpluggled the battery, reset my computer, and disabled

my "AFC-select" maf voltage controller.

After a few runs through the rpm range for the computer to learn the new setup

everything seems to be working very nice.

I have to say.... I think overall the engine feels stronger and more refined now.

My peace of mind feels much better as well since I know for sure that the

proper air measurement is working with the fuel maps as designed from Porsche,

rather than a "calibrated" signal to trick the computer.

Afr readings at wide open throttle are around 13 from low to mid rpms and then drops

to around 12.5 for the upper rpm range.

My initial impressions are that the car feels more responsive. Hard

to say for sure because it was running quite fast before as well. Just seems to be more

sorted out all around with partial throttle response being a bit more aggressive and

then full throttle applications feeling a bit stronger up top.

Since I have tried both methods I think overall, this is the way to go.

Especially for peace of mind and knowing that you are taking full advantage of the

way the 996 3.4 liter ecu was programed originally with the larger maf housing.

I Think I will keep it like this for awhile ;^)

[1999Porsche911]

Right around 340 ohm works well for a stock 996 program using a stock boxster maf housing. I would put in a variable pot resistor, this will allow you to 'tune' the fuel trims right where you want them. 1999 explained this to me a few years ago when I did my first 3.4 conversion. I still think the best solution is to use a properly sized intake tract, as I'm not convinced that the small boxster intake system can flow enough air to feed the 3.4. Look how porsche increase the airbox size when they put the 3.4 into the 987 vs the 986.

-Todd

I wanted to give a quick update on my current setup as of last night ...

After 7 months of running a "calibrated" maf signal

I finally decided to track down the proper MAF housing size and got my hands

on Todd's recommended "Cayman/Boxster 987" Maf housing . Brand new from

Sunset Porsche parts the discount is still a lot ... $275 because it includes

the actuall sensor which I can not use.

All I wanted was the housing tube to plug my boxster/996 sensor into. I finally tracked

down the proper size maf housing from a dismantler and saved myself

over $200...It also has the screen built into it to help with air turbulence.

In the process I also discovered a proper sized nice alternative

Bosch maf housing for a lot less $$ then Porsche... (pm me if interested)

My original 986 boxster maf housing measures inner diameter of 70-72mm.

(76mm or 3 inch outer diameter)

The 3.4 liter 996/Cayman maf housing measures inner diameter of 83-85 mm

(90mm outer or 3.5 inch outer diameter)

A difference of close to 20 percent in size.

With my "calibrated" maf signal my air fuel ratios were staying a solid 12-12.5 and the car was running very strong.

Even so I still felt that "tricking" the ECU with a calibrated signal or resistor may not be taking full advantage

of all the fuel maps and how they were designed to work with proper air flow measurement from Porsche.

Even though I really enjoyed my setup there was always a question in my mind if I

was really allowing the programming to work correctly under those "calibrated" conditions.

Since I want my 3.4 Boxster to run it's strongest at all times I decided it was time to

switch over to the proper maf housing size.

After modifying intake tube lengths for the new housing I got

it to fit nicely.

My current intake setup is:

-Cone filter plugs onto front end of Cayman Maf Housing..

-back end of housing plugs onto 3 inch intake tubing all the way to Throttle body.

(996 throttle body is only 3 inches in diameter)

I unpluggled the battery, reset my computer, and disabled

my "AFC-select" maf voltage controller.

After a few runs through the rpm range for the computer to learn the new setup

everything seems to be working very nice.

I have to say.... I think overall the engine feels stronger and more refined now.

My peace of mind feels much better as well since I know for sure that the

proper air measurement is working with the fuel maps as designed from Porsche,

rather than a "calibrated" signal to trick the computer.

Afr readings at wide open throttle are around 13 from low to mid rpms and then drops

to around 12.5 for the upper rpm range.

My initial impressions are that the car feels more responsive. Hard

to say for sure because it was running quite fast before as well. Just seems to be more

sorted out all around with partial throttle response being a bit more aggressive and

then full throttle applications feeling a bit stronger up top.

Since I have tried both methods I think overall, this is the way to go.

Especially for peace of mind and knowing that you are taking full advantage of the

way the 996 3.4 liter ecu was programed originally with the larger maf housing.

I Think I will keep it like this for awhile ;^)

The reason for your difference in A/f at WOT is because your calibrated signal was different than it is now. Running at WOT at a 13:1 air fuel ratio will make your car feel like it has more pep since you are running lean.......maybe too lean. Especially running 91 octane fuel. Had you calibrated the signal with a higher ohm restistor, you would have had the exact same results.

Edited August 6, 2009 by 1999Porsche911

[qikqbn]

Right around 340 ohm works well for a stock 996 program using a stock boxster maf housing. I would put in a variable pot resistor, this will allow you to 'tune' the fuel trims right where you want them. 1999 explained this to me a few years ago when I did my first 3.4 conversion. I still think the best solution is to use a properly sized intake tract, as I'm not convinced that the small boxster intake system can flow enough air to feed the 3.4. Look how porsche increase the airbox size when they put the 3.4 into the 987 vs the 986.

-Todd

Since I have tried both methods I think overall, this is the way to go.

Especially for peace of mind and knowing that you are taking full advantage of the

way the 996 3.4 liter ecu was programed originally with the larger maf housing.

I Think I will keep it like this for awhile ;^)

The reason for your difference in A/f at WOT is because your calibrated signal was different than it is now. Running at WOT at a 13:1 air fuel ratio will make your car feel like it has more pep since you are running lean.......maybe too lean. Especially running 91 octane fuel. Had you calibrated the signal with a higher ohm restistor, you would have had the exact same results.

Thats what I enjoy about the maf signal controller that I have. I can see an immediate response to

air fuel ratio fine tuning from the drivers seat.

I am still able to do very fine tuning and adjust the voltage signal if I see any strange

spikes or make any intake changes in the future.. but now with the new housing I do not have to make

any voltage corrections at the moment. I just did the change last night so I am still feeling out the changes.

I may fine tune a little bit later, but for now its nice to have a factory setting starting

point, which I felt I was sort of guessing at before.

I really enjoyed the "calibrated" setup I had before and it worked great for the most part..

It is definitely a great alternative, but now I just feel like I have the best of both worlds.

Factory setting air fuel ratios with the ability to fine tune.

Thanks for your input 1999, I always learn a lot from you.

Bill

[Jinster]

Bill, do you have any info on how to wire up the Apexi-Select? Which wires to tap into and where?

I think Apexi rolled out AFC-Neo, as a replacement for the SAFC and VAFC. Not sure if "Select" is incorporated into the new Neo.

[Mother]

I'm a late comm-er to this thread but great read.

Edited October 8, 2009 by Mother

[wwest]

Maybe a great read, I just finished, but totally, TOTALLY idiotic.

The sole control of A/F mixture during engine idle or "cruise" is left to the upstream oxygen sensors, closed loop. During these periods, mixture STRICKLY controlled to stociometric, the MAF/IAT signal levels (now operating under known, controlled, intake airflow conditions) are "captured" for later use filling in a parametric mapping table to be used under/with higher engine load/loading conditions wherein the mixture MUST be enriched beyond the measurement capability, range, of the oxygen sensors.

The MAF/IAT module/assembly is only able to measure the actual intake airflow volume/rate in a very small area of the intake airflow path, a snapshot, if you will. So the overall, total intake airflow volume must be calculated from that rather small sample. Add a CAI, Cold Air Intake, ANYTHING that impacts the calculation of intake airflow volume and the factory parameters used to facilitate the intake airflow volume from the small (area wise) sample might become USELESS.

Like the clock fully stopped only being correct twice a day, your A/F mixture will only be "correct" for engine idle or cruise periods.

Oh, since other than at WOT times the throttle plate constitutes the primary restriction then any intake airflow modifications that impact flow volume will have little or no adverse effect except at or near WOT.

Just what yawl needed to hear, right..!!

[1999Porsche911]

Maybe a great read, I just finished, but totally, TOTALLY idiotic.

The sole control of A/F mixture during engine idle or "cruise" is left to the upstream oxygen sensors, closed loop. During these periods, mixture STRICKLY controlled to stociometric, the MAF/IAT signal levels (now operating under known, controlled, intake airflow conditions) are "captured" for later use filling in a parametric mapping table to be used under/with higher engine load/loading conditions wherein the mixture MUST be enriched beyond the measurement capability, range, of the oxygen sensors.

The MAF/IAT module/assembly is only able to measure the actual intake airflow volume/rate in a very small area of the intake airflow path, a snapshot, if you will. So the overall, total intake airflow volume must be calculated from that rather small sample. Add a CAI, Cold Air Intake, ANYTHING that impacts the calculation of intake airflow volume and the factory parameters used to facilitate the intake airflow volume from the small (area wise) sample might become USELESS.

Like the clock fully stopped only being correct twice a day, your A/F mixture will only be "correct" for engine idle or cruise periods.

Oh, since other than at WOT times the throttle plate constitutes the primary restriction then any intake airflow modifications that impact flow volume will have little or no adverse effect except at or near WOT.

Just what yawl needed to hear, right..!!

And what happens during closed loop when the MAF is reporting substantially incorrect flow numbers? O2 sensors can only adjust so much, BTW: The MAF itself is little more than a set of resistors housed in a nice expensive piece of plastic. The only difference between the 996 and the TT MAF is just a different set of resistors. The MAF signal is important in both open and closed loop operation.

Edited October 9, 2009 by 1999Porsche911

[catmanluge]

My problems was solved by readjusting the height of the fuel injectors. Because I used the Boxster Fuel Rails the that required new brackes to fit on the 3.4 intake they were set to low. Raising the fuel rails slightly solved my problem.

[qikqbn]

Bill, do you have any info on how to wire up the Apexi-Select? Which wires to tap into and where?

I think Apexi rolled out AFC-Neo, as a replacement for the SAFC and VAFC. Not sure if "Select" is incorporated into the new Neo.

Sorry for the late response Jinster....

If you are still interested in seeing some wiring diagrams

you can download a few here'

http://www.apexi-usa.com/info/?id=5383

these will give you an idea... they are a bit technical and

the afc-select for german cars can only be found on ebay

or yahoo shopping since it was discontinued and replaced

by newer units...

I have the special diagrams for the boxster if interested

that show the wiring harness and what number ecu terminal

to plug into.

Basically you open up the wiring harness to the ecu and there are 5 wires

to connect. Throttle position, knocking signal, power, rpm, airflow signal.

4 wires are just tapped into the existing wires, know cutting required.

The only wire that is "cut" is the airflow signal. Once the air signal wire

is cut, you splice the incoming signal to go to the AFC-select airflow input.

then attach the AFC-select airflow output wire and splice it onto

the other half of the cut airflow signal wire that goes directly into

the ecu terminal.

The wiring itself seemed very straightforward and simple. The setup of the

actual AFC unit to read the signal properly and adjust to the different rpm ranges

took a little bit of patience and testing. I highly recommend having a air fuel

ratio gauge wideband.

Overall it is a really interesting product and worked

wonders for fine tuning my air fuel ratio. It was the answer to my prayers

at the time. Since then I have installed the cayman s maf housing, so

my tuning with the afc select is still usefull, but not needed quite as much

as before.

send me a message if you need to see the actual diagram and I can scan it for ya.

Bill...