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Question for BMC filter users and my theory re: MAF's and CAI'


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Hi all,

I have a 99 C2 and some of you may recall I tried the K & N CAI a few months back. I thought I had escaped the dreaded mass air flow problems that so often accompany these aftermarket intakes, but I was mistaken as mine eventually crapped out after a few months. I returned the unit, bought a new MAF (after repeated attempts at cleaning didn't help), and all is now well. HOWEVER, I miss the sound and slightly improved (real or percieved) throttle response and power that the CAI unit provided.

I thought hard about trying the evo unit, which I've heard from others is less likely to kill a MAF, but I've decided against it for the following reason:

There seem to be two theories concerning why the aftermarket intakes cause MAF problems: oil residue fouling the maf, and "non-laminar" flow over the resistor in the MAF sensor (i.e., flow that is turbulent instead of flow that is flat and orderly, which supposedly is the type of flow provided from the stock and other flat panel filters). My bet is that the real culprit is not oil, but rather the turbulent flow. This would explain, for example, why the later cars with the updated MAF sensor design (which features a couple of turns in the air ducting that could serve to "straighten" the flow of air before its hits the wire) seem to fair better than the earlier cars (although it could just be that the earlier cars have older MAF's that are closer to failure anyway, and that the CAI just hastens its already imminent failure). THis would also explain why the evo units, which feature a bit more distance between the MAF and the filter (that could theoretically result in less turbulent flow) seem to provide less problems than the K & N unit (the K & N unit positions the MAF sensor pretty close to the filter). If it was an oiling issue, it seems that both CAI brands would cause problems at similar rates, although this seems, at least anectdotally, not to be the case.

So, I think my solution is to add a schnell/fabspeed/home depot intake kit which blocks off the resonator, which would, at the minimum, give me a little more sound. This seems like a pretty benign mod as it does not appear to affect pre-MAF sensor air flow. However, I am thinking about also adding a BMC or K & N replacement filter for a bit more flow, which leads me to my question, which I hope will help me test my theory that the oil on a properly (i.e., minimally) oiled filter is not the real culprit:

For those who have installed JUST a K & N, BMC, or other flat-panel replacement filter that requires oiling and made no other intake mods, what has been your experience? Dead MAF sensor or is it still alive? I'd also be interested in the year of the car and the length of time the filter has been in use. If there are folks that have had problems with just the change to an oiled filter, I think I'll stay away and just settle for blocking of the resonator. Thanks!

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Hi Scott.... I share my experience....it may, or may not help, or be exactly what you are looking for. Today, I stick with stock intakes and paper filters (GT3, Audi S4 TT), but, I did experiment with intake mods on my '99 C4. I bought it new in Feb, '99 and sold it in July '03 with about 48K on it. Shortly after purchase I put on a K&N panel in the stock box. I'm always careful about over oiling and about letting it "age" overnight before reinstalling. I've read all the horror stories about failed MAFs, but, in my case I never had a problem. About a year later, when Joe Fabiani was "inventing" his intake system for 996's, I began to experiment (not using Joe's parts). At that time Evo had something I think they called a "quick flow" or something like that for not a lot of money. I bought that and stared at it for a while. I used the quick flow's main big plastic angle tube and silicone tubes and clamps to eliminate the "nasty" accordian tube. Then I built my own resonator eliminator. Actually I just unscrewed and removed it and plugged the hole with (get this) an old 2 1/8th inch VDO instrument hole knock-out plug. I glued it in with RTV and it fell out. I re-glued it in with epoxy and it worked fine (even though it wasn't carbon fiber). I got the intake sound from the K&N panel, the larger air box volume (for whatever that may or not be worth) and got whatever effects on intake flow that eliminating the resonator produced. Then I just drove the thing another 40K miles and enjoyed it.

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Hi Scott, I have a 2001 996 c4 cab. I had the EVO unit on my car and it caused PSM, ABS, and Check Engine Lights to come on. The car also had shut off while at freeway speeds. I bought a new MAF and installed it with the same results. I then replaced the EVO with the stock unit and the old MAF and guess what? No problems at all. I have had oiled filters on other vehicles with no problems. I think the problem with the Porsche MAF is the turbulence in the new intake. My car would get the codes mostly upon shifting at high speed into 3rd gear and would shut off upon deceleration from around 70 MPH.

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I have had a K&N filter in my 1999 Boxster for over 50k miles. I have cleaned and reoiled it once, being very careful to not over-oil it and to make sure (using a fan) it is dry before reinstalling it.

I had absolutely no problems until I installed an EVO high flow intake (less than 10k miles ago). About 600 miles later, I got a CEL (P0102 - MAF sensor voltage too low). I replaced the MAF and about 600 miles later I got the same error. I checked all of the wiring for correct voltages and connectivity and checked the tubing for leaks. No problems detected.

Then I put the stock air intake (with K&N filter) back in hoping the problem would resolve itself. It didn't, even after thousands of miles of driving.

I just replaced the MAF again today. Given that I went tens of thousands of miles with K&N in and had no problem, I am thinking that there is no issue with K&N. And K&N is quite vigorous about defending claims about their filters causing problems. In fact they will replace your MAF if it a problem with it is determined to be a result of their filter.

In summary, I don't think there is an issue with using K&N as long as you don't over-oil it.

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