maf sensor no screen problem?

hey guys quick question on my 02 p5 my car keeps bogging out once and a while so i decided to take a look at the maf sensor but it has no screen on it is that a problem or it shouldn't matter? let me know thanks

I read a thread about removing it on purpose. It's supposed to help air flow and MPG. Another mod in the same thread mentioned about cutting away the part of the cowl right above the snorkel input to help with positive pressure for the intake. Some people worry about rain pushing it's way into the intake but I haven't had a problem. I did that mod but haven't done the MAF screen yet but I think I will. The only problem might be blowing out the air filter and pieces going directly into the engine. I'm not too worried about that.

I found a cople of pictures of the intake MOD

Yes, it won't allow the maf to get a proper reading, it's there for a reason

^I never thought about that,... I'll try to find that thread again and see if they mention that.

The honeycomb thing is to 'scatter' intake charge across the MAF...it breaks up the wall of air coming through, so the sensor can meter a little better...at the cost of being slightly restrictive...it is only useful at on/off throttle changes...meaning the instant air starts moving, or stops suddenly...so, realistically, it only effects throttle response to a very slight degree...

over my ownership of the car...all of which so far (other than a brief stint with another engine) has been with the stock intake system...i've had that thing out for 30,000+ miles...then put it back in, etc...i personally could never tell if it did anything...it had NO effect on my gas mileage...the only difference it made for me was a slightly different intake sound at idle...

PCB...that mod seems pretty pointless to me...if anything, just remove that 'snorkel' altogether...i haven't had one for most of my cars life...my header melted the bottom of it in about a month...and i just pulled it out...i hit a deer a few years later, and the dealership installed a new snorkel (assuming it was destroyed by the deer? it wasn't even in there haha)...so i removed it again, before melting it...

all that thing does is acts as a sound suppressor ..without it, you'll hear a little more intake noise...but thats it...in 130,000+ miles and TONS of rain...i've never come close to getting any water in the engine...

The screen on the MAF is to make the airflow linear and remove buffeting and turbulence for more accurate readings of the air. (nothing to do with "scattering" or spreading the flow) Most cars will run without it but often as not show mild to moderate drivability problems like the OP describes. The bogging out happens when air flows just wrong across the sensor due to turbulence or angled flow causing a reading that doesn't match reality.

Yes removing the screen does allow for a greater flow rate but you usually have a net loss from the inaccurate measurement causing problems. By the time the MAF is actually a 'restriction' to the power you're making, you should be running a different engine management computer that uses a larger (appropriate) MAF or none at all (IE speed-density)

I see the same stuff on the F-body forums for the LT1 and LS1. Yes removing the screen increases the airflow capacity by X% but you see a net LOSS on the dyno and track times

Installshield 2 said:

PCB...that mod seems pretty pointless to me...if anything, just remove that 'snorkel' altogether...i haven't had one for most of my cars life...my header melted the bottom of it in about a month...and i just pulled it out...i hit a deer a few years later, and the dealership installed a new snorkel (assuming it was destroyed by the deer? it wasn't even in there haha)...so i removed it again, before melting it...

all that thing does is acts as a sound suppressor ..without it, you'll hear a little more intake noise...but thats it...in 130,000+ miles and TONS of rain...i've never come close to getting any water in the engine...

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The cutout in the cowling is supposed to give a sort of "ram air" effect. At speed, the air pushes through the grill and directly into the snorkel mouth. The guy in the thread describing it, took pressure measurements before and after the cut-out and found a constant positive air pressure with the cut out but had negative pressure at different rpms and speeds before the cut-out. He said as well that there was no water issues getting into the snorkel, even when in driving rain.
I'm having trouble finding the original thread, I don't remember the title.

I've decided to keep my screen in.

kamesama980 said:

The screen on the MAF is to make the airflow linear and remove buffeting and turbulence for more accurate readings of the air. (nothing to do with "scattering" or spreading the flow) Most cars will run without it but often as not show mild to moderate drivability problems like the OP describes. The bogging out happens when air flows just wrong across the sensor due to turbulence or angled flow causing a reading that doesn't match reality.

Yes removing the screen does allow for a greater flow rate but you usually have a net loss from the inaccurate measurement causing problems. By the time the MAF is actually a 'restriction' to the power you're making, you should be running a different engine management computer that uses a larger (appropriate) MAF or none at all (IE speed-density)

I see the same stuff on the F-body forums for the LT1 and LS1. Yes removing the scream increases the airflow capacity by X% but you see a net LOSS on the dyno and track times

Click to expand...

ok...maybe scattering wasn't the best adjective...I meant scattering of pressure gradients (turbulence resulting in 'buffeting' as you put it)...I wasn't meaning it had anything to do with spreading out flow after the air gets moving properly...it just breaks up uneven walls of air that are caused by quick changes of throttle position...

in either case...i've driven this car with and without it long enough to confidently say that $.25 piece of plastic isn't going to make any noticeable difference to the cars behaviour...a true dyno might see a slight change, but your body will not...and while i had it out, i had absolutely not drive ability problems or changes in any way...

Installshield 2 said:

ok...maybe scattering wasn't the best adjective...I meant scattering of pressure gradients (turbulence resulting in 'buffeting' as you put it)...I wasn't meaning it had anything to do with spreading out flow after the air gets moving properly...it just breaks up uneven walls of air that are caused by quick changes of throttle position...

in either case...i've driven this car with and without it long enough to confidently say that $.25 piece of plastic isn't going to make any noticeable difference to the cars behaviour...a true dyno might see a slight change, but your body will not...and while i had it out, i had absolutely not drive ability problems or changes in any way...

Click to expand...

Ah, right idea, words fell short. It happens. Just want to make sure everyone's on the same page.

I disagree. You need way more than that screen to smooth the flow (if anything - it disrupts any linear flow prior to the MAF). Picture that screen being waved through a tank of water - all the eddies and currents.... And the precision lost to the air turbulence is minimal (Like 'measuring with a micrometer and cutting with an ax' so to speak...

It is there to ensure no big failure of the air filter jams the sensor or gets in the engine[.]

The 'ram air mod' is moderately effective and no, the hole in the box will drain any rainwater injested. Drive through the puddle that covers the intake and you are skrewed.

The low and high pressure gradients have to be seen in a 'dynamic way' - the intake is a suction - so it is a low pressure point to begin with. If the intake is located in a high pressure 'area' - then (by definition) it is getting a high pressure input - masked by the suction low pressure)... a good thing.


Bottom line - i removed my screen to decrease the restriction (a weee bit) and accepted the risk of a filter failure. No negative impact in >200K miles...

The guy in the thread about the two mods (the thread that I can't seem to find again) made his own semi-accurate pressure gauge and tested the "relative" air pressures before and after the intake mod. He found that before the mod there was a small vacuum created in the intake (relative to air pressure inside the cabin) by the suction of the intake. After the hole was cut there was an increase in pressure (relative to cabin pressure) through out the intake system. So instead of the intake sucking in air and creating a vacuum, the ram-air effect pressurized the entire intake.

^^we're all saying roughly the same thing...if you picture water moving through the screen; yes it will create some weirdness to the flow...what we're saying is that the MAF needs that weirdness in specific conditions...

you're absolutely right on the intake vacuum creating a low pressure void around the opening...the problem is...its not a uniform gradient because its intensity is directly related to throttle position...

Air is elastic, its just a big invisible spring...when you ram open the throttle plate, not all the air starts moving in uniform fashion right away...you get uniform pockets of different densities...after a few seconds of sustained throttle position, the pockets diminish and the air moves uniformly for the most part...until you change that throttle position again, and this starts all over again...

thats what the screen is for...it breaks up those pockets a little bit...This isn't a part that has anything to do with the driver, or the engine's out right performance...it has to do with how the sensor is calibrated, and how closed loop biased the government wants these computers to be...In closed loop, the computer is listening to measurements taken after a cycle occurred and needs very accurate measurements of intake charge in order to quickly adapt...the screen helps reduce statistical out-liars that would be caused by buffeting...resulting in more engine cycles being deemed U-LEV compliant under closed loop...

removing it...no big deal...you'll never know the difference...Its only a very small piece of the bigger U-LEV puzzle...these engine's aren't set up all that great for closed loop to begin with, for reasons beyond the scope of this post...which is why the honey comb filter has little effect in or out...low speed throttle response has plenty of room for improvement, even with a screen like this...its just a 'it won't hurt' type of thing from the factory...but i promise its not just a thing to prevent a 'blockage' to the intake system..if that was the case it would've been placed behind the maf, in case the MAF needle broke off for some reason...if that happened, it most definitively would get to the throttle body at least...

just out of curiosity i went and logged a drive with the screen in place, and without it...in the log i can clearly see the MAF readings remain slightly more consistent during big changes to throttle position...without the screen, the MAF readings (and mandated AFR's because of it) go through some bumps for a few cycles before it corrects itself...neither of which i can feel in engine behavior, but according to Torque Pro, its there...

pcb said:

I'm having trouble finding the original thread, I don't remember the title.

Click to expand...

I found the original article about this modification. There is a link in the first post that covers all the testing procedures.

http://www.clubprotege.com/forum/showthread.php?1977-Modifying-the-Stock-Air-Intake-System