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Air Intake Whistling noise


July 13, 2008
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Year, Model & Trim Level
2006 Explorer V6 4.0

I have a 2006 XLT 4.0L v6 explorer that was stock, until I recently installed a custom dual exhaust on it (AMAZING sound), along with a KKM air intake. I have noticed that after the installation of the KKM intake, there is a whistling sound whenever I push on the accelerator. It is super high pitched and super annoying. I have read some threads on here, and apparently the whistle is a common problem on the v6 4.0. Has anyone ever successfully fixed this problem? It seems as though no one has figured out how to fix it.

Also, how important/useful/much performance would be gained by installing a heat shield?

Thanks in advance.

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I dont think that could be it. This is the 06 and it looks nothing like what was in that video. Also, the loud sound (a whistle, much like you try to suck in with your lips closed) didn't start until AFTER I installed the air intake.

Anyone? I know many of you reported this same specific problem after installing the KKM Air Intake on 2006 Explorer's v6 4.0's. Did everyone just have to live with it, or could anyone fix it?

Warren Kurtz, founder of KKM, posts here (as KKM) and said in the thread that it was an issue with another part of the car being loose. It doesn't make the noise when I put it in park and rev it, but it makes it (mostly between 1000 and 2500rpm) when Im driving and accelerating.

I have the same problem and made a post about it last year, his response was:

I would suggest checking the areas mentioned on any whistling noise. I can't say there have been more than 2-3 people on the newer integrated style airbox systems with a whistle noise. Asside from the obvious IAC valve issues that plagued older models, you might look into the areas of the crankcase vent line as a possible source for the noise.

This was the thread

My '07 has a slight whistle even with the STOCK intake FWIW...

I have tried absolutely everything and it comes down to how the throttlebody takes the air. The only reason you hear it with the cold air intake is because you now have an open intake. if you put your air intake to stock again and listen, you can hear the whistle faintly. It got so annoying I finally took my CAI off and just go with a regular stock replacement K&N. If anybody has different info, I would love to hear it. Some things I have done....
sealed all connections with tape
changed the size and shape (even disconnected) crankcase ventilation
took off those goofy plastic add on pieces (one looks like a "j" the other a rectangle) and plugged those holes.
None of this had any effect. I have wondered for some time if I install a tornado (cheap garbage that has no effect on mileage or hp) hopeing that it will change the airflow enough to get rid of the noise, but I haven't tried it or heard of anyone trying it. I would be embarrased to buy one in person, I would have to order online.
If anybody has info or help I would appreciate it also, but to be clear, this is the noise that comes within a 500 rpm range around 2200rpm. Not the tpi noise and not the ventilation noise coming from the air/heat unit.

holy crap, dude i have the same problem...but i dont think its your add exhaust is stock and just hit 36000 miles....and now i hear the high pitchg whistling sound when i hit my accelerator too....i try to convince my self it aint a thing but after reading this post this might be a problem...mine is a 06 too

ya, i need to check that valve on mine and see if that changes anything.. Iv been around the block with mine also - changing to a KN filter, covering holes, leaving the box open, trying all sorts of differnet options, however i never thought that it might be somthing else causing the problem..

While i hear nothing at idle, im still wondering if that may be the problem.

The video shown seems to be having the issue at idle, and i cant hear it at that point, only from 1800 - 2200 or so. however i suppose it cant hurt to try.

I know it's been awhile, but has anyone found a solution to the air intake whistle yet? I had my KKM for a year and never had any issues, but I recently had my explorer serviced at which time they replaced the TPS and since then I've been getting the high pitched whine on acceleration. I took it back to Ford and they said the noise is the aftermarket intake and they have a TSB that says aftermarket intakes will make this type of noise on the V6 explorers. I just don't see how I could go a year with no noise and suddenly it's making it after being serviced.

I have the same sound too I had it ever sense I put AEM universal intake on now I have KKM and its not as bad.... tell yourself that its the turbo spooling up lol

I have a 91 ranger all stock and I have the same whistle sound from 10 mph on up. It does sound like a turbo an aweful lot. any help would be greatly appreciated.

Wow, I'm actually really relieved to hear that others have the whistling noise. I thought it was just me. I have an '08 4.0L, completely stock. It makes a really annoying whistle when accelerating at engine speeds of ~2k to 2.5k. I took it to the dealer a couple times. They were convinced it was the transmission and took the whole thing apart twice, but it didn't change at all. Fortunately it was all covered by the powertrain warranty, and they even gave me a rental car. It was still really frustrating to drive off the lot after they "fixed it" and hear that whistle as soon as I pulled onto the street. After the second time, they just told me the noise was "normal" for that truck. I did get a new torque converter and a completely unnecessary transmission rebuild for free though, so I can't complain about that. So don't let anyone tell you it's the transmission, folks.

An air intake issue makes much more sense. I thought maybe a vacuum leak, but it runs great - no rough idle or anything like that. If it is a vacuum leak, it would have to be very small.

One thing I find really strange, and I would really like to know if anyone else has noticed this, but it seems to change with temperature and/or humidity. It's much more noticeable on cold foggy days than on hot dry days. Is that a useful clue at all? Also, it has got worse over time. I didn't notice it at all when I first bought it a year ago.

My '06 also has a whistle under partial load in the 1800-2500rpm range. It really sounds like an induction noise, most likely from behind the throttle body. Could be from an air flow issue (mis-match between the throttle body bore and the intake flange or an air leak somewhere in the intake, seals or hose connections maybe. I haven't looked into it yet but I will ask by Ford engineering buddy if he knows about this issue.

I brought my '07 Explorer in as well and I've had a bunch of transmission problems "due to the sound." When I got my car back, they told me that the noise was normal. It's quite irritating. I've brought it to another dealership as well and they can't figure out what is wrong. Same symptoms, usually happens around 2500 RPM. I really can't stand hearing that sound, makes the car seem so unrefined. If anyone has a solution please help! I have also noticed about the temp. changes and yes my problem does get worse depending on the weather conditions.

I have an '06....I just take it as a performance

ya, if it sounds like a turbo or a procharger, i would just go with it. haha

My 05 with a CAI does that whistle, but the inhaling is louder now. I just tell myself its the sound of a turbo. When I had my Spectre Intake a whistle was much more prominent, but I don't really care not likes its too annoying, IMO.

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Thank God I found this thread! I have the same damn problem. 2006 XLT 4.0 4x4. I can't tell you how many garages I have been to and had mechanics listen, taken them for rides and most of them say they can't hear it. Not sure how you can be a mechanic and not have a keen sense of hearing, but anyway. It's exactly the same as everyone posts here...when I'm on the throttle moderately between 1500-2500 rpm and it sounds very much like a turbo, just with none of the power! Ha. I thought it was a vacuum situation as well, but not noticing any of the other performance issues that would go along with a vacuum leak. PLEASE PLEASE PLEASE let's find a solution to this issue. I'll check back and definitely let you know if I come across anything.