Additional info on Mass Air Sensor screen removal for HP/Torque improvement.

The Mass Air Sensor attached to the stock airbox in our BMW is a standard hot wire unit put out by Seimens and designed for throttle-by-wire systems. The purpose of the MAF screens is to the disbelief of others is not as a debrit screen or to prevent large objects from entering the engine although may be a secondary effect. What was noted by Seimens is that the backpressure wave effect caused by the closing of the throttle plate at high speed with the added incoming air velocity interrupts the accurate calculations of airflow and causes a lean condition which the screens help prevent. We have to account for the fact the BMW engines were built in Germany and built for speeds in excess of 100MPH. Well I can tell you I have been over 105MPH without the screens and I haven't run into this problem and in the US it is unusual that you would drive long distances in the 100-120MPH range as in Europe. Also the increased airflow velocity acts to cool the sensor wires better and results in higher performance, since the basis of the wire is to convert the difference of the heated wire when cooled to voltage. This is how it determines the airflow velocity. Seimens has since come out with a new mass air sensor that allows more airflow but has a third heater wire after the first two wires which allows it to re-heat the air before it enters the engine.

The real purpose of the two screens are:

Primary Grate Screen: Straighten airflow and reduce airflow turbulance.

Secondary Mesh Screen: Reduce airflow velocity, act as a deflector for any incoming dirt and water particles. Reduce the backpressure waves created by the opening and closing of the throttle so that air flow can be accurately read.

Typically removing the screens leads to improved performance due to the increased airflow velocity. On some vehicles it has lead to performance degredation. Some experts contend in certain vehicles it can lead to the engine running to rich or to lean, just as with a cold air intake. Software adjustments are needed to take advantage of the increased airflow by adjusting the air/fuel ratio and spark advance as well as short and long trim adjustments. However, ECM systems as well as other sensor measurements factor in when not running tuned software. The increased airflow is adjusted for withing the limits of the ECM, to protect the catalytic converter from overheating as well as meet emissions requirements. This is why we can get away with a CAI and no tuned software.

The same will hold true for other tweaks such as increased throttle body size or even increased mass air sensor size or just mass air sensor screen removal. The effect of such tweaks is again, causing miscalculations with the volumetric efficiency of the engine and the calculations built into the ECM. Someone with expertise in ECM/DME programming would be able to tell us the limitations but eventually you would cause a calculation error and a engine light would result.

I chose to go back to my stock airbox while having the mass air sensor screens removed. The reasons is the restriction caused by the airbox will reduce the turbulant airflow as well as the internal velocity stack will assist in smoother airflow without the MAF screens over the MAF hot wire. In addition, there is added safety. After three days without the screens, I have noted improved acceleration greater than when I had my CAI in. With the CAI, low end RPM was only slightly improved until you reached over 3000 RPMs. With the screens out, acceleration starts from idle RPM. The acceleration is throughout the RPM range. The exhaust and engine note has a deeper tone. I reset my MPG yesterday to see if the increased airflow is causing the fuel injectors to put out more gas and thus degreased MPG.






DISCLAIMER

DISCLAIMER owner modification to BMW OEM Components

The information in this message thread in its entirety related to modifying the OEM BMW Mass Air Sensor is based on personal opinion. By modifying the components of your vehicle this immediately voids your warranty for such parts or any related parts or components so affected. It should also be noted that the owner of such vehicle takes full responsibility for any and all damages related to said component(s) modification or secondary mechanical failures as such related. The vehicle owner additionally grants any and all information providers as to the nature, indications, findings, tip, speculation, rumor, fact, or otherwise non-qualified opinion, hold-harmless.



B's edit - Added the disclaimer to the first post in this thread

Kevin,


Where'd you get this info from?!?

Any info on the non-throttle-by-wire E46s MAS?



-Brent

I tried this on my 95 M3 years ago and the car ran like ****...stumbled and the idle was all over the place.

The only people I know that have done it and seen gains are cars with FI on them.

My $.02

The major difference was the introduction in the e46 after 2000 of throttle-by-wire as well as better engine management. I see no idle problems or stumbling problems in any RPM range with the screens off on my 2001 325ci. Now this is not to say with the increased intake diameter in a 330 that the net performance results will be the same but I doubt any issue such as check engine light would occur since even adding a larger diameter throttle body in a 330 won't trip it or a CAI for that matter.

There was a thread on DTMPower apparently by a BMW tech who said you could adjust the throttle cable which essentially is faking out the ECM on throttle position. Do a search here since I reposted this a while ago. Maybe search on my screen name and DTMPower or DTM Power might find it.

Originally posted by B
Kevin,


Where'd you get this info from?!?

Any info on the non-throttle-by-wire E46s MAS?



-Brent

I've just paid for my GruppeM which I should hopefully have soon. It is suggestable to remove the screens and give it a go ?

Thanks,
Stuart.

i'll confirm kevin's results with the MAF screens removed but on a 330

definately jumpier from the line with my step. i think the sound of the engine is a little more pronounced as well

Stuart I'd just like to thank you for giving me such pleasure in looking at your car, I havent been here long but so far you have the best 330CI by far!!!

I thought you were in the UK when I saw your sig with the number plate Your in Portugal aren't you ?

Thanks,
Stuart.

Originally posted by KevinJ_2k1_325ci


There was a thread on DTMPower apparently by a BMW tech who said you could adjust the throttle cable which essentially is faking out the ECM on throttle position. Do a search here since I reposted this a while ago. Maybe search on my screen name and DTMPower or DTM Power might find it.

really? remember any tidbits from it?!?

seems like a cheap mod to do LOL. can anyone post a short DIY with pics of how to do this?

Caution kiddies you may not want to try this at home :o)

As far as the screens, it looks like it has two holes in the front where they seal it, but it's not sealed but probably the holes that are used to when pouring the plastic into the mold. I took a 2 1/2 inch nail and a pair of plyers and bent the head of the nail in a L shape (the head, not the sharp nail end). The screen is one piece and space seperating the front plastic grate from the rear metal mesh screen. So the L shape should be very short so you don't poke the mesh screen. I then angled the nail though a square hole at the bottom edge and using the plyers slightly pulled the nail. Essentially I made a hook to pull the screen out. I then repeated slightly and slowly at the top and bottom, back and forth from top to bottom untill the screen slid out. I hooked on the bottom edge not on one of the actual grates in like the middle so I wouldn't break one. The front screen is not like the back which is small and easy to pop out. The front is thicker and sets deeper in the MAF. I wouldn't worry about the back screen since it is not restrictive at all.

Here's a link to pics that xmltok took:
MAF Screens removed

I'm seeing performance throughout the range from idle (500 rpm) to redline. As I eluded to in my original post above, I think the larger mass air sensor diameter, intake tube diameter, and throttle body diameter limits the amount of increase you will see in the 330.

A word of caution folks, remember you are playing with a $600 sensor. If your not willing to risk damaging it, then donot perform this mod.

Hopefully someone with a 325 can confirm my results as xmltok has already done on a 330.

Originally posted by xmltok
i'll confirm kevin's results with the MAF screens removed but on a 330

definately jumpier from the line with my step. i think the sound of the engine is a little more pronounced as well

I had problems accessing the link earlier when i was talking with xmltok. Can anyone else access it or is it just me that can't

So the benefits are less on a 330 compared with a 325 ? what about cars with intakes ? We'll give it a go anyway whats a $600 sensor hehe.

Thanks,
Stuart.

No warning light come on from doing this?

From what I understand all you are doing it allowing the MAF sensor to get better readings by removing the screens which are restricting air flow. So is sounds as though your allowing the sensor to do what its supposed to do, whereas at the minute its being hampered slightly ?

Stuart.

From the pics that xmltok posted, It looks like the 330 MAF has some sort of sensor brace attached to it on the inside? My 325 MAF just has the sensor hanging down and no cross brace.

Kevin.......so would you recommened this for someone like me with a CAI, chip and exhaust??? TIA

problems viewing the webpage should be fixed now, if its still a problem you will have to wait for your nameservers to refresh

and my maf did have a brace, the 325 does not?

Essentially this is correct. But you would need someone with expert tuning knowledge such as Jim Conforti who knows the inner workings of the ECM and mototronics to be able to get measured results that the increased airflow is boosting performance in one area and robbing from another. Such as you getting better low end RPM and torque but upper HP is affected. As though we drive 135mph everyday anyway. Also raw results would be shown on a dyno.

Basically increased air velocity adds more torque than hp and you can confirm that through dyno testing. You can for example look on ECIS's website at some of the CAI dyno tests. Adding additional volume will add more HP than torque which is turbo or supercharging or intake runner modification which will yield some volumetric gains as well.

The change from removing the screens possibly could throw off the calculations for volumetric efficiency that BMW engineers accounted with the tolerance levels in the induction system, intake manafold, and catalytic converter but I believe are adjusted for because of throttle-by-wire and engine management and better O2 and manafold sensors. If it were throwing off the scales, then the ECM would default to a default profile which would essentially assure the engine is runnable and you would see the condition that Sean described with hesitation in the engine.

Since the e46 was built as a single vehicle for a world market, the tolerance levels should be wide. For example, they designed for the fact that you could live in a cooler region, or hotter, high or low altitute, or have varying levels of fuel quality. This is what fmakes the e46 so much different from previous models which were essentially geared toward segments of the market and they made engine adjustments depending on where in the world you live. Most of the adjustments can be done in software now as opposed to hardware and they just slap in a different ECM module depending on the country to meet their environmental policies. Realistically it is the components if you read the manufactures web sites, that are really doing most of the work not BMW. BMW probably uses Seimens engine management well.

If for a millisecond, this was causing the BMW to do something it was not supposed to or able to adjust for, you would see a "Service Engine Soon" light. As Seimens the manufacturer indicated, at high speed the effect of the back pressure wave can report miscalculations of airflow. Also the increased airflow cools the MAF hot wire which sends signals for less fuel which could make it think it's getting more air BUT you have to remember the intake manafold pressure sensor would be sending data to the ECM as well so it would know.

Originally posted by -=Stu=-
From what I understand all you are doing it allowing the MAF sensor to get better readings by removing the screens which are restricting air flow. So is sounds as though your allowing the sensor to do what its supposed to do, whereas at the minute its being hampered slightly ?

Stuart.