# 100mm MAF screen experiment to address part-throttle tip-in stumble, lean codes, and surging when coming to a stop.



## 'dubber (Jun 15, 2004)

What's up people, I've been chasing down an issue with partial throttle tip-in stumble as well as idle surging or loping when approaching a stop, ultimately leading to lean codes. I've had this pretty much since day one of the turbo kit. After a lot of checking and re-checking for issues with my setup (Kinetic obd-1 coilpack 36 tune, which uses a 4 inch maf housing but does not include a flow straightener) in terms of faulty parts or vac leaks, etc, and finding none, and a lot of internet research of anecdotal accounts of solutions to similar problems, I have decided to experiment with these things: 

http://www.saxonpc.com/100mm-cells-for-100.html 

I know that a lot of people who don't have airflow screens have had similar issues and some have solved them by moving the air filter away from the maf, or moving the airfilter and maf away from the turbo and dv tube, and they all seem to be doing this in an effort to reduce turbulant air from hitting the maf, and that's fine, but these straighteners seem like a cheaper and easier next step for me vs. concocting a cold air intake from raw tubing. 

Many manufacturers put these flow straighteners in their cars from the factory.
Aftermarket modification companies catering to Audi and Corvette owners and probably others seemed to begin selling these things with their cold air intakes and turbo kits after running without them started to cause the same issues that I'm having. As long as I'm still outflowing or at least coming close to the smallest bottleneck in the chain I won't feel bad about putting this into the intake airstream if it helps the drivability. Even if I lose some hp up top due to airflow restrictions then I should still be able to safely throw a couple more psi at it to make up for that. 

For around fifty bucks shipped, I bought two sets of three flow rates in 100mm diameter. I plan to start off by placing one rated for the most flow in front of the maf, and then the second behind it if one offers only some improvement, and then switch to the smaller ratios in the same steps and see if any combos seem to offer any improvement, and I'll post up if anything works.


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## TBT-Syncro (Apr 28, 2001)

i tried several configs with my old setup, i found that the honeycomb after the maf sensor made the biggest difference (one before made almost no difference).

now i just run a pro-maf sensor, and dont have to worry about it.


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## GinsterMan98 (May 19, 2008)

I remeber seeing a picture of that, was it custom or did you buy it somewhere?


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## 'dubber (Jun 15, 2004)

Tbt, im not sure how a pro maf programmed for 36 lb injectors and installed into a housing with no laminar flow screen would change anything. I would think that it would behave like the setup that i have now. ( oem maf sensor, 4" housing, and no flow straightener. ). Im sure that you are using much larger injectors than i do which needs the pro maf for proper signal to feed those bigger injectors. What am i not understanding?


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## TBT-Syncro (Apr 28, 2001)

'dubber said:


> Tbt, im not sure how a pro maf programmed for 36 lb injectors and installed into a housing with no laminar flow screen would change anything. I would think that it would behave like the setup that i have now. ( oem maf sensor, 4" housing, and no flow straightener. ). Im sure that you are using much larger injectors than i do which needs the pro maf for proper signal to feed those bigger injectors. What am i not understanding?


you're right in that you'd need injectors matched to the tune/sensors. however, the pro-maf is a much better quality sensor, and not as susceptible to inaccuracy due to turbulence based off of how it gets a reading. So in situations where an OEM sensor gets inaccurate readings, the pro-maf sensor would be fine.


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## TBT-Syncro (Apr 28, 2001)

GinsterMan98 said:


> I remeber seeing a picture of that, was it custom or did you buy it somewhere?


custom. used aluminum lighting diffusers.


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## GinsterMan98 (May 19, 2008)

Nice! never would have thought of that.


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## GinsterMan98 (May 19, 2008)

> What am i not understanding?


The main diffrence between a stock maf and the pro maf is how it gets its readings. Your factory maf is constantly sending airflow values to your ecu, so any change in airflow will get sent to the ecu no matter how large the or small the value is. This is bad because during periods of uneven flow the ecu is making a lot of changes to compinsate and it can cause the lean and stumble issues, which I have. The pro maf does the same thing except it sends an average of several readings to the ecu, so it keeps the signal much more accurate, thereby keep fueling much more stable during periods of uneven flow in the maf. I am going to try this when I get home. 

Thanks to both of you for the info.


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## 'dubber (Jun 15, 2004)

Advanced apologies for all of the words below. :beer:

Ok, so I received the stuff in the mail today and eagerly opened the box to see exactly what I was getting. The metal ones have the largest honeycomb patterns and the highest flow rating. The middle-flow ones are plastic and have a smaller honeycomb pattern and are just as tall as the max-flow ones. The lowest-flow ones have the same honeycomb size as the mids, but are taller which ends up reducing the velocity I think. But the I'm pretty sure that the lowest-flow ones will not fit and still allow me to clamp everything together because of the height difference. 

Anyway, I took the two high-flow ones and placed one right in the air filter collar in front of my maf housing, and the other in the silicone tube which necks down from 4" to a smaller dimension soon after the maf housing and clamped it all back together. I thought long and hard about the possibility of these things collapsing and getting sucked into the turbo, but they seem very strong and do not move once everything is clamped down. 

I then proceeded to disconnect the battery to drain the ecu capacitors in order to wipe the stored fuel trims. Once I reconnected the power, I fired it up and let it idle for a few minutes, and then went for a little spin, then shut it off and restarted it and let it idle again for a couple of minutes. This usually sets the idle pretty well under any circumstances. Then I went for a good drive, trying to vary the rpms in second and third using the mid range of the throttle. I learned somewhere that this is the best procedure for initially resetting the ecu fuel trims. I then drove around on familiar routes and did stuff that I'm used to doing to see if it made any difference. 

First, the cons. The car does seem a bit down on power, not a lot, but a bit. I attribute this to stuffing a bunch of crap into the intake tract. The pros are that drivability is basically like it was how I remember it being before the turbo kit. In other words, no issues. Mind you, I've only put about 15 miles on it since shoving those things in there, but not once after doing the idle set procedure did it bog, buck, stumble, stall, or give any indication that it was not running well. Normally after resetting the ecu, it will be ok for like three miles and then start acting up. I'm really stoked. 

My plan is to drive it as I have it now with two screens for one week. Then I'll attempt to remove one of the screens and reset the ecu again, and see what happens in an attempt to free up the intake a little. If it's just as good, I'll drive for a week, and then I'll take out the other one and put the first one back in and reset and see which combo works the best. Mabye I'll find that I can use one screen but of the smaller honeycomb pattern, but I'll keep updating with any info here. Ideally, I'm hoping to only have to use one screen, be it in front of or after the maf, but if I have to use two the way I have it now with one in front and one behind, the loss in power that I am detecting does not seem too bad. Hell, I amy be imagining it. I took the car drag racing a couple days ago before I had the screens, so I have a rough baseline of sorts to see how much faster or slower the car is with the screens the next time I go to the track. I also need to plug my laptop into my zeitronix output and look at the maf voltage graphics. I remember that it always looked very choppy so I want to see if that is any smoother. I'll be driving a lot over the next few days and will report back if it all goes to crap or if it basically stays good.


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## carsluTT (Dec 31, 2004)

TBT-Syncro said:


> custom. used aluminum lighting diffusers.


u have any pics of this, sounds interesting.


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## GinsterMan98 (May 19, 2008)

Thanks for posting bro! Good Shiz!


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## 'dubber (Jun 15, 2004)

Just an update, after driving with a number of different combinations, it seems that the smoothest one is using two high-flow metal screens, one just in front of the maf sensor, and one just behind it. I am experiencing the drivability issues still, but they seem to take a lot longer to develop and the car recovers more smoothly over a longer period of time, so in essence, this is just a band-aid that seems to increase the amount of time between ecu resets. 

I did go ahead and install a cold air intake, with the maf still in stock position, but I had the intake cut so that if I flip it around and lengthen my maf sensor wiring, I should be able to move the sensor further away from the DV hose and turbo, which I will try at some point.


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## Boost112 (May 8, 2002)

'dubber said:


> Just an update, after driving with a number of different combinations, it seems that the smoothest one is using two high-flow metal screens, one just in front of the maf sensor, and one just behind it. I am experiencing the drivability issues still, but they seem to take a lot longer to develop and the car recovers more smoothly over a longer period of time, so in essence, this is just a band-aid that seems to increase the amount of time between ecu resets.
> 
> I did go ahead and install a cold air intake, with the maf still in stock position, but I had the intake cut so that if I flip it around and lengthen my maf sensor wiring, I should be able to move the sensor further away from the DV hose and turbo, which I will try at some point.


....when you say high flow metal screens... what ratio are you referring to? i am about to order two of them and just wanted to make sure that i get the correct one.... i was thinking 5:1 ratio metal screens from saxonpc.com...

tia....


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## GinsterMan98 (May 19, 2008)

I used the 5:1 ratio about 3 inchs in front of the MAF. I am running a home made MAF housing.


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## Boost112 (May 8, 2002)

GinsterMan98 said:


> I used the 5:1 ratio about 3 inchs in front of the MAF. I am running a home made MAF housing.



... how has it been working for you so far? im thinking of picking up two screens...one for before and after maf...

...thanks for the response...


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## GinsterMan98 (May 19, 2008)

Great, I can say with great excitement that my car has ZERO stumble at any throttle input level. It also gets 30 mpg on the highway. Much better than the 24 mpg and stumble issues I had with the 30# setup.


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## DannyLo (Aug 2, 2006)

I might have to attempt this. My car definitely has those little stumbles when tipping onto throttle after a shifting, and other little hiccups at and close to idle.

C2 Ramhorn is just a 4" sewer pipe with the MAF inches from the filter.


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## SVTDanny (Aug 8, 2005)

GinsterMan98 said:


> Great, I can say with great excitement that my car has ZERO stumble at any throttle input level. It also gets 30 mpg on the highway. Much better than the 24 mpg and stumble issues I had with the 30# setup.


I should know from your previous posts, but OBD1 or 2?


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## 'dubber (Jun 15, 2004)

Boost112 said:


> ....when you say high flow metal screens... what ratio are you referring to? i am about to order two of them and just wanted to make sure that i get the correct one.... i was thinking 5:1 ratio metal screens from saxonpc.com...
> 
> tia....


When I bought them, the highest flow rate screen was metal. The two others were plastic with the middle flow rate screen being shorter than the lowest flow rate screen.


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## GinsterMan98 (May 19, 2008)

djsheijkdfj said:


> I should know from your previous posts, but OBD1 or 2?


 OBD2


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