Fuel Air Mixture

[catmanluge]

Loren

I have placed a 3.4 carrera engine in a Boxster. It generally runs well except that I have noticed that its is running richer than normal. The exhaust pipes are black rather than grey. How is the fuel air mixture controlled? Can it be adjusted? How can this be acomplished?

Thanks

Catmanluge :renntech:

[Loren]

Todd Holyoak is the expert on these swaps but I think it would be helpful to know:

- which fuel intake did you use

- did you go from egas (Boxster engine) to egas (Carrera engine)

The only adjustment I know is to program the DME as either a Boxster or Carrera program.

[catmanluge]

Todd Holyoak is the expert on these swaps but I think it would be helpful to know:

- which fuel intake did you use

- did you go from egas (Boxster engine) to egas (Carrera engine)

The only adjustment I know is to program the DME as either a Boxster or Carrera program.

I went from an E-Gas Boxster to a non E-Gas carrera engine but purchased an E-Gas intake manifold and throttle body so I could use the Boxster Throttle Pedal .

I do have a Cold Air Box system with Headers and a free flow exhaust...

Todd did my DME

Catman

[catmanluge]

Todd Holyoak is the expert on these swaps but I think it would be helpful to know:

- which fuel intake did you use

- did you go from egas (Boxster engine) to egas (Carrera engine)

The only adjustment I know is to program the DME as either a Boxster or Carrera program.

I went from an E-Gas Boxster to a non E-Gas carrera engine but purchased an E-Gas intake manifold and throttle body so I could use the Boxster Throttle Pedal .

I do have a Cold Air Box system with Headers and a free flow exhaust...

Todd did my DME

Catman

PS In addition I use the fuel lines from the Boxster with the injectors from the Carrera

[Stefan]

There is no adjustment for the mixture. That is done automatically based on sensor data. One or more sensor could be reporting the wrong value.

Is it idling high? It could be a vacuum leak.

[JeTexas]

There is no adjustment for the mixture. That is done automatically based on sensor data. One or more sensor could be reporting the wrong value.

Is it idling high? It could be a vacuum leak.

If it had a vacuum leak, I think it would be running lean, but the sooty exhaust would make me think it is running rich.

Do you get an codes for 02 sensors? Do you still have the cats on the exhaust?

[catmanluge]

There is no adjustment for the mixture. That is done automatically based on sensor data. One or more sensor could be reporting the wrong value.

Is it idling high? It could be a vacuum leak.

If it had a vacuum leak, I think it would be running lean, but the sooty exhaust would make me think it is running rich.

Do you get an codes for 02 sensors? Do you still have the cats on the exhaust?

It idles around 750 RPM I have had a few codes P1275 and P1276. I have HiFlow Cats with the O2 sensors on each side of the cats on both exhaust pipes.

[Loren]

P1275 Signal Delay Time for Oxygen Sensor Ageing, Bank 1 – Above/Below Limit

P1276 Signal Delay Time for Oxygen Sensor Ageing, Bank 2 – Above/Below Limit

Potential causes:

– Oxygen sensor ahead of TWC

– Leak ahead of TWC or in the area of the oxygen sensor after TWC

– Wiring (oxygen sensors exchanged)

[tholyoak]

Common problem with swaps. I'll give you a hint, look at the diameter of a 986 MAF housing and compare it to the diameter of a 996 MAF housing. There are a couple of solutions.

-Todd

[catmanluge]

Common problem with swaps. I'll give you a hint, look at the diameter of a 986 MAF housing and compare it to the diameter of a 996 MAF housing. There are a couple of solutions.

-Todd

Todd

I am running 3.5 inch tubing from the air filter to the TB. The MAF is located in a 3.5 inch metal tube that comes off the rear of the air box.

[KevinMac]

Unleaded fuel will always leave black deposits on the exhaust pipes. They old grey was from lead. The unleaded fuel based on it's chemical makeup, specifically MTB, will not leave grey on the tailpipes. So if you are using this as an indication that it's running rich, you are not diagnosing correctly. You need a fuel air ratio count.

Pull the plugs and read the plugs, this should be a good indicator. Does the exhaust smell rich, are you seeing black exhaust?

Edited July 22, 2008 by KevinMac

[tholyoak]

As Loren's post shows, based upon the error codes you posted, you do not have a mixture problem. If you truly have a mixture issue, PM me your fuel trim values and I'll see if I can't help you take care of it.

-Todd

[JeTexas]

If the car is running well, and you're not getting error codes, my guess is that the higher flow cats/exhaust are just letting more soot through. I had a car with no cats, and althought I kept it tuned perfectly, I was still wiping black off the exhaust tips every time I washed it.

[catmanluge]

As Loren's post shows, based upon the error codes you posted, you do not have a mixture problem. If you truly have a mixture issue, PM me your fuel trim values and I'll see if I can't help you take care of it.

-Todd

Todd

How do I go about get the Fuel trim values?

Bill

[KevinMac]

Still not sure why you think you have a mixture poblem. The codes presented point to O2 sensors. You may running up the wrong tree based on false assumptions.

Edited July 23, 2008 by KevinMac

[tholyoak]

As Loren's post shows, based upon the error codes you posted, you do not have a mixture problem. If you truly have a mixture issue, PM me your fuel trim values and I'll see if I can't help you take care of it.

-Todd

Todd

How do I go about get the Fuel trim values?

Bill

Bill, they are the FRA and TRA values that you can monitor with your Durametric.

-Todd

[catmanluge]

As Loren's post shows, based upon the error codes you posted, you do not have a mixture problem. If you truly have a mixture issue, PM me your fuel trim values and I'll see if I can't help you take care of it.

-Todd

Todd

How do I go about get the Fuel trim values?

Bill

Bill, they are the FRA and TRA values that you can monitor with your Durametric.

Thanks Great I will let you know!

-Todd

[qikqbn]

I realize these posts were awhile ago, but I know there are many of us still dealing with this problem of our MAF sensor

causing rich or lean AFR's when we start adding bolt ons. I have had a major break through and wanted to share

the solution I came upon.

I have a 98 boxster with a 3.4 liter conversion. I have had it over a year this way and have been driving it using very

rich AFR's for most of the time. My AFR's have been reading in the 10's for quite awhile. Even this way the car was making

decent power, about 310 at the crank, but with all of my modifications I should have been closer to 320-330.

ECU Tuning has been a break through, but not how you think. I originally had "powerchip group" reprogram my ecu rom, but after 3 different programs and 3 100 mile round trips to their facility I was still running very rich. I then contacted "Steve", owner of SR Motorsports in Gardena (310-516-1003) for some dyno tuning. He has some amazing experience with tuning import cars and was in the research and development for APEX products for 5 years. I was running very rich for awhile and my Air fuel ratio readings were around 10 under wide open throttle on the dyno. The basic idea we discovered is that the MAF housing diameter for the stock 996 is 3.5 inches. For the Boxster it is 3 inches. When the 3.4 liter motor is drawing in air it is pulling air in "faster" through the smaller boxster 3 inch MAF instead of the stock 996 3.5 inch housing it was oringinally programmed for. This "faster/higher" reading sends a voltage reading to the996 ecu that calls for more fuel and thus richens everything at wide open. The opposite can happen if your MAF housing gets too big.

We wanted to be able to fine tune as needed so Steve recommended the "APEX AFC-SELECT" for german cars.

http://www.apexi-usa.com/product_electroni...5&pageNum=1

Hard to find these days, but they are out there. I also installed an AEM wideband Air fuel ratio gauge to monitor AFR's from within my car. The APEX AFC-Select allows us to control the voltage reading of the MAF at any designated rpm before it gets to the 996 ecu. By doing so the 996 ecu takes the new voltage reading and adjusts the fuel injectors as required. Thus we were able to fine tune my AFR to read a conservative 12 all across the board. From this tuning alone I gained 20-30 lbs of torque and horsepower across the mid rev range from 3500-7000 rpm. I was stunned and amazed at the difference! The whole process of installation and tuning took about 3 hours. Now I have a system that I can fine tune to my unique modifications. I would highly recommend this procedure over any "ecu rom tuning" in a heart beat because everyone's car mods are different. This eliminates wondering if your "reprogrammed chip" needs to be adjusted if you ever ad anymore bolt ons.

Steve's knowledge of the product and ease of use was paramount to making it happen so smoothly..Now granted this is not adjusting timing and other parameters that rom chips do, but for most bolt on mods that deal with faster air flow this is a great solution.

We wanted to start out conservative and tuned the air fuel ratio to hold 12 across the entire rev range at wide open throttle. We will later be raising it to an AFR of 13 which should result in a gain of another 10-15 hp and tq. For this test we will keep it conservative and safe at 12 for a few 100 miles to make sure no check engine lights or problems show up..

My before and after dynojet peak dyno readings at the wheels were as follows:

base: 255hp @ 6300 and 215tq @ 4600 (wheels) X 1.2 = 306 hp and 258 tq at crank

AFR=12 flat :270hp @ 6300 and 235tq @ 4600 (wheels) X 1.2 = 325 hp and 282 tq at crank

compare this with a bone stock 300 hp 2001 996 3.4 dynojet:

251hp and 213tq X 1.2 = 300hp and 256tq at crank

AFR=13 flat

Car has now been dyno'd with close to 325 hp at the crank and weighs only 2750 lbs.

Gtech Pro RR g-force meter performance run:

*adjusted

0-60 foot launch 1.9 sec

0-60 mph in 4.4 sec

0-100 mph in 10.5 sec

0-130 mph in 17.2 sec

0-150 mph in 27 sec

Quarter mile time 12.7 sec @ 110 mph.

Edited January 6, 2009 by qikqbn

[1999Porsche911]

I realize these posts were awhile ago, but I know there are many of us still dealing with this problem of our MAF sensor

causing rich or lean AFR's when we start adding bolt ons. I have had a major break through and wanted to share

the solution I came upon.

I have a 98 boxster with a 3.4 liter conversion. I have had it over a year this way and have been driving it using very

rich AFR's for most of the time. My AFR's have been reading in the 10's for quite awhile. Even this way the car was making

decent power, about 310 at the crank, but with all of my modifications I should have been closer to 320-330.

ECU Tuning has been a break through, but not how you think. I originally had "powerchip group" reprogram my ecu rom, but after 3 different programs and 3 100 mile round trips to their facility I was still running very rich. I then contacted "Steve", owner of SR Motorsports in Gardena (310-516-1003) for some dyno tuning. He has some amazing experience with tuning import cars and was in the research and development for APEX products for 5 years. I was running very rich for awhile and my Air fuel ratio readings were around 10 under wide open throttle on the dyno. The basic idea we discovered is that the MAF housing diameter for the stock 996 is 3.5 inches. For the Boxster it is 3 inches. When the 3.4 liter motor is drawing in air it is pulling air in "faster" through the smaller boxster 3 inch MAF instead of the stock 996 3.5 inch housing it was oringinally programmed for. This "faster/higher" reading sends a voltage reading to the996 ecu that calls for more fuel and thus richens everything at wide open. The opposite can happen if your MAF housing gets too big.

We wanted to be able to fine tune as needed so Steve recommended the "APEX AFC-SELECT" for german cars.

http://www.apexi-usa.com/product_electroni...5&pageNum=1

Hard to find these days, but they are out there. I also installed an AEM wideband Air fuel ratio gauge to monitor AFR's from within my car. The APEX AFC-Select allows us to control the voltage reading of the MAF at any designated rpm before it gets to the 996 ecu. By doing so the 996 ecu takes the new voltage reading and adjusts the fuel injectors as required. Thus we were able to fine tune my AFR to read a conservative 12 all across the board. From this tuning alone I gained 20-30 lbs of torque and horsepower across the mid rev range from 3500-7000 rpm. I was stunned and amazed at the difference! The whole process of installation and tuning took about 3 hours. Now I have a system that I can fine tune to my unique modifications. I would highly recommend this procedure over any "ecu rom tuning" in a heart beat because everyone's car mods are different. This eliminates wondering if your "reprogrammed chip" needs to be adjusted if you ever ad anymore bolt ons.

Steve's knowledge of the product and ease of use was paramount to making it happen so smoothly..Now granted this is not adjusting timing and other parameters that rom chips do, but for most bolt on mods that deal with faster air flow this is a great solution.

We wanted to start out conservative and tuned the air fuel ratio to hold 12 across the entire rev range at wide open throttle. We will later be raising it to an AFR of 13 which should result in a gain of another 10-15 hp and tq. For this test we will keep it conservative and safe at 12 for a few 100 miles to make sure no check engine lights or problems show up..

My before and after dynojet peak dyno readings at the wheels were as follows:

base: 255hp @ 6300 and 215tq @ 4600 (wheels) X 1.2 = 306 hp and 258 tq at crank

AFR=12 flat :270hp @ 6300 and 235tq @ 4600 (wheels) X 1.2 = 325 hp and 282 tq at crank

compare this with a bone stock 300 hp 2001 996 3.4 dynojet:

251hp and 213tq X 1.2 = 300hp and 256tq at crank

AFR=13 flat

Car has now been dyno'd with close to 325 hp at the crank and weighs only 2750 lbs.

Gtech Pro RR g-force meter performance run:

0-60 foot launch 1.9 sec

0-60 mph in 4.4 sec

0-100 mph in 10.4 sec

0-130 mph in 16.5 sec

0-150 mph in 26 sec

Quarter mile time 12.7 sec @ 110 mph.

Nice job, but it would be alot easier to simply make your MAF have a variable signal. Maf would be calibrated one way in closed loop which would allow the O2 sensors to properly managed the a/f and then would switch to the another calibration in open loop. You then have a fully adjustable MAF signal and full control of your a/f ratio in a matter of seconds.

Edited December 10, 2008 by 1999Porsche911

[catmanluge]

I realize these posts were awhile ago, but I know there are many of us still dealing with this problem of our MAF sensor

causing rich or lean AFR's when we start adding bolt ons. I have had a major break through and wanted to share

the solution I came upon.

I have a 98 boxster with a 3.4 liter conversion. I have had it over a year this way and have been driving it using very

rich AFR's for most of the time. My AFR's have been reading in the 10's for quite awhile. Even this way the car was making

decent power, about 310 at the crank, but with all of my modifications I should have been closer to 320-330.

ECU Tuning has been a break through, but not how you think. I originally had "powerchip group" reprogram my ecu rom, but after 3 different programs and 3 100 mile round trips to their facility I was still running very rich. I then contacted "Steve", owner of SR Motorsports in Gardena (310-516-1003) for some dyno tuning. He has some amazing experience with tuning import cars and was in the research and development for APEX products for 5 years. I was running very rich for awhile and my Air fuel ratio readings were around 10 under wide open throttle on the dyno. The basic idea we discovered is that the MAF housing diameter for the stock 996 is 3.5 inches. For the Boxster it is 3 inches. When the 3.4 liter motor is drawing in air it is pulling air in "faster" through the smaller boxster 3 inch MAF instead of the stock 996 3.5 inch housing it was oringinally programmed for. This "faster/higher" reading sends a voltage reading to the996 ecu that calls for more fuel and thus richens everything at wide open. The opposite can happen if your MAF housing gets too big.

We wanted to be able to fine tune as needed so Steve recommended the "APEX AFC-SELECT" for german cars.

http://www.apexi-usa.com/product_electroni...5&pageNum=1

Hard to find these days, but they are out there. I also installed an AEM wideband Air fuel ratio gauge to monitor AFR's from within my car. The APEX AFC-Select allows us to control the voltage reading of the MAF at any designated rpm before it gets to the 996 ecu. By doing so the 996 ecu takes the new voltage reading and adjusts the fuel injectors as required. Thus we were able to fine tune my AFR to read a conservative 12 all across the board. From this tuning alone I gained 20-30 lbs of torque and horsepower across the mid rev range from 3500-7000 rpm. I was stunned and amazed at the difference! The whole process of installation and tuning took about 3 hours. Now I have a system that I can fine tune to my unique modifications. I would highly recommend this procedure over any "ecu rom tuning" in a heart beat because everyone's car mods are different. This eliminates wondering if your "reprogrammed chip" needs to be adjusted if you ever ad anymore bolt ons.

Steve's knowledge of the product and ease of use was paramount to making it happen so smoothly..Now granted this is not adjusting timing and other parameters that rom chips do, but for most bolt on mods that deal with faster air flow this is a great solution.

We wanted to start out conservative and tuned the air fuel ratio to hold 12 across the entire rev range at wide open throttle. We will later be raising it to an AFR of 13 which should result in a gain of another 10-15 hp and tq. For this test we will keep it conservative and safe at 12 for a few 100 miles to make sure no check engine lights or problems show up..

My before and after dynojet peak dyno readings at the wheels were as follows:

base: 255hp @ 6300 and 215tq @ 4600 (wheels) X 1.2 = 306 hp and 258 tq at crank

AFR=12 flat :270hp @ 6300 and 235tq @ 4600 (wheels) X 1.2 = 325 hp and 282 tq at crank

compare this with a bone stock 300 hp 2001 996 3.4 dynojet:

251hp and 213tq X 1.2 = 300hp and 256tq at crank

AFR=13 flat

Car has now been dyno'd with close to 325 hp at the crank and weighs only 2750 lbs.

Gtech Pro RR g-force meter performance run:

0-60 foot launch 1.9 sec

0-60 mph in 4.4 sec

0-100 mph in 10.4 sec

0-130 mph in 16.5 sec

0-150 mph in 26 sec

Quarter mile time 12.7 sec @ 110 mph.

Nice job, but it would be alot easier to simply make your MAF have a variable signal. Maf would be calibrated one way in closed loop which would allow the O2 sensors to properly managed the a/f and then would switch to the another calibration in open loop. You then have a fully adjustable MAF signal and full control of your a/f ratio in a matter of seconds.

Interesting -- Sounds like a direction I should look at!

Thanks for you write up!

[tholyoak]

Personally I think using the correctly sized MAF housing is the proper way to fix this. But as 1999 says, there is a much easier way to solve this problem by using a simple resistor to 'calibrate' the MAF signal for the smaller housing.

-Todd

[qikqbn]

Nice job, but it would be alot easier to simply make your MAF have a variable signal. Maf would be calibrated one way in closed loop which would allow the O2 sensors to properly managed the a/f and then would switch to the another calibration in open loop. You then have a fully adjustable MAF signal and full control of your a/f ratio in a matter of seconds.

hey 1999-911 and Todd, I have read a lot of your posts on conversions and Thanks for all your input and knowledge...you guys rock!

I actually got my hands on a stock 996 air box with the intention of cutting out the MAF housing to use with my

cold air intake... well, as you already know... not so easy. I then tried to find some 3.5 inch tubing and create my own

MAF housing to mimic this as well, but gave up. The idea of fine tuning won me over in the end.

You both have great ideas and options with the similar idea of controlling the MAF signal, but how exactly do you rig it to be able to do that?

How do you control when it switches from "closed" to "open" loop calibration? Is it a throttle position or rpm?? Is it a unit you buy and splice

into the maf signal wire at the ecu? what's it cost?

The AFC-select works a bit like that. 4 wires are connected at the ecu to monitor Throttle position, power, MAF signal, knock sensor. The maf signal wire

is the only wire altered so that the signal is sent to the AFC-select unit and then a "new corrected signal wire" is sent back into 996 ecu.

What I was impressed with on AFC-select is the ability to designate exactly which rpms to correct voltage % on and at what throttle position I wanted to adjust the signal on. For example: If on the dyno my MAF signal at 70% throttle position (tp) is already giving a rich afr of 10. Below 70% tp the afr is ok.

So in this scenario by throttle position 70% I wanted the the voltage corrected by -20%. I can create the parameters for the

throttle position like this: at 20% tp = 0% voltage correction...correction would ramp up smoothly so that by 70% throttle position and above = 100% preset voltage correction is reached. (voltage correction being preset at -20%) This allows us to have a nice smooth linear correction on MAF signal output.

then we fine tuned every few hundred rpms to smooth out any bumps or dips in the AFR readings.. After all was said and done we made about 15 runs on the dyno as we adjusted the signal correction little by little to make sure of never running too lean.

Is there a way to do this type of callibration with a simple resistor to alter the MAF signal?

I am all for any solutions or ideas to help. Especially since a lot of us have gone down the bolt on mods and conversion routes only

to be disappointed when things are not running properly and as expected. After a couple hundred miles this weekend I am very pleased. Now I have to just

keep my fingers off from tinkering with the computer to get that last little .01% correction ;) I also find myself watching my afr reading like crazy whenever I accelerate at wot. It has been great though and holds 12.0 afr pretty solid. Sometimes too many gauges are a distraction! :o

What AFR's do you find to be ideal and safe??

Thanks again for your input. it is greatly appreciated.

Bill

Edited December 10, 2008 by qikqbn

[1999Porsche911]

hey 1999-911 and Todd, I have read a lot of your posts on conversions and Thanks for all your input and knowledge...you guys rock!

I actually got my hands on a stock 996 air box with the intention of cutting out the MAF housing to use with my

cold air intake... well, as you already know... not so easy. I then tried to find some 3.5 inch tubing and create my own

MAF housing to mimic this as well, but gave up. The idea of fine tuning won me over in the end.

You both have great ideas and options with the similar idea of controlling the MAF signal, but how exactly do you rig it to be able to do that?

How do you control when it switches from "closed" to "open" loop calibration? Is it a throttle position or rpm?? Is it a unit you buy and splice

into the maf signal wire at the ecu? what's it cost?

The AFC-select works a bit like that. 4 wires are connected at the ecu to monitor Throttle position, power, MAF signal, knock sensor. The maf signal wire

is the only wire altered so that the signal is sent to the AFC-select unit and then a "new corrected signal wire" is sent back into 996 ecu.

What I was impressed with on AFC-select is the ability to designate exactly which rpms to correct voltage % on and at what throttle position I wanted to adjust the signal on. For example: If on the dyno my MAF signal at 70% throttle position (tp) is already giving a rich afr of 10. Below 70% tp the afr is ok.

So in this scenario by throttle position 70% I wanted the the voltage corrected by -20%. I can create the parameters for the

throttle position like this: at 20% tp = 0% voltage correction...correction would ramp up smoothly so that by 70% throttle position and above = 100% preset voltage correction is reached. (voltage correction being preset at -20%) This allows us to have a nice smooth linear correction on MAF signal output.

then we fine tuned every few hundred rpms to smooth out any bumps or dips in the AFR readings.. After all was said and done we made about 15 runs on the dyno as we adjusted the signal correction little by little to make sure of never running too lean.

Is there a way to do this type of callibration with a simple resistor to alter the MAF signal?

I am all for any solutions or ideas to help. Especially since a lot of us have gone down the bolt on mods and conversion routes only

to be disappointed when things are not running properly and as expected. After a couple hundred miles this weekend I am very pleased. Now I have to just

keep my fingers off from tinkering with the computer to get that last little .01% correction ;) I also find myself watching my afr reading like crazy whenever I accelerate at wot. It has been great though and holds 12.0 afr pretty solid. Sometimes too many gauges are a distraction! :o

What AFR's do you find to be ideal and safe??

Thanks again for your input. it is greatly appreciated.

Bill

The easiest and most effective way is to simply get an adjustable vacuum switch similar to the one shown in the link below. The MAF signal #5 wire would be cut with the DME side of the wire going to the common on the switch and the MAF side of the cut wire to BOTH switchable leads on the switch. The switch is activated by vacuum, switching from one lead to the other depending on whether vacuum is present or not. The default lead (vacuum present) would be connected to the MAF side of the cut wire without resistor and the other lead would be connected to the MAF side of the wire with a resistor the size which will give you the A/F ratio you want at WOT. You could also put a rheostat inline to make it easy to test different settings

Using the above method, you maintain the current tubing configuration of the intake and it allows an easy way for fine tuning in a matter of seconds.

The easiest and most effective way is to simply get an adjustable vacuum switch similar to the one shown in the link below. The MAF signal #5 wire would be cut with the DME side of the wire going to the common on the switch and the MAF side of the cut wire to BOTH switchable leads on the switch. The switch is activated by vacuum, switching from one lead to the other depending on whether vacuum is present or not. The default lead (vacuum present) would be connected to the MAF side of the cut wire without resistor and the other lead would be connected to the MAF side of the wire with a resistor the size which will give you the A/F ratio you want at WOT. You could also put a rheostat inline to make it easy to test different settings

Using the above method, you maintain the current tubing configuration of the intake and it allows an easy way for fine tuning in a matter of seconds.

http://images.google.com/imgres?imgurl=htt...l%3Den%26sa%3DN

Edited December 11, 2008 by 1999Porsche911

[qikqbn]

The easiest and most effective way is to simply get an adjustable vacuum switch similar to the one shown in the link below. The MAF signal #5 wire would be cut with the DME side of the wire going to the common on the switch and the MAF side of the cut wire to BOTH switchable leads on the switch. The switch is activated by vacuum, switching from one lead to the other depending on whether vacuum is present or not. The default lead (vacuum present) would be connected to the MAF side of the cut wire without resistor and the other lead would be connected to the MAF side of the wire with a resistor the size which will give you the A/F ratio you want at WOT. You could also put a rheostat inline to make it easy to test different settings

Using the above method, you maintain the current tubing configuration of the intake and it allows an easy way for fine tuning in a matter of seconds.

http://images.google.com/imgres?imgurl=htt...l%3Den%26sa%3DN

hey 1999....

very clever! So I noticed that on that particular switch you can "preset" a vacuum pressure with a little screw. Is there a certain psi needed before

the switch kicks in or do you just have it switch at the slightest vacuum change? I would assume you would figure out the vacuum pressure at a certain throttle position so that it switches close to wot???

I figure there are a lot of different resistor sizes to try out and picking the right one sounds like a lot of trial and error... The rheostat sounds like the way to go and you can just turn the knob down to dial lower the maf signal......aaaahaaaa... very interesting. Gotta know what rheostat resister range to chose though... , but what if you need a "stronger" signal because you are running too lean? hmmm

last question... since it is an "on/off" switch method based on vacuum there is not a lot of fine tuning involved, Kind of a one adjustment fixes all and then just leave it....... so how is driveability? can you feel it switching so quickly between the 2 maf signals?

Thanks for the info, that was very eye opening...very cool.

[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.

Edited December 11, 2008 by 1999Porsche911