rasping noise at certain rpm
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This is a discussion on rasping noise at certain rpm within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; hey guys my head is wrecked cause i cant figure out what this noise is. firstly the noise seems to ...

  1. #1
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    rasping noise at certain rpm

    hey guys

    my head is wrecked cause i cant figure out what this noise is. firstly the noise seems to happen when the car is warm and very rarely when shes cold. the rasping noise starts approaching 4000rpm and finishes just before 4300rpm approx. the noise only happens in 1st, 2nd and 3rd but mostly second. from inside the car it sounds like the noise is coming from middle front to middle middle area. oh yeah and it only happens under load which makes it even harder to diagnose. if anybody has any ideas please let me know or if you need more info just ask. also check light on maf and knock but im nearly sure its not related and gearbox crunch form 3rd to 4th and 4th to 3rd im thinkin syncro & baulk rings etc so again im nearly sure its not related to this particular noise. any help much appreciated

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  3. #2
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    Quote Originally Posted by jicesd View Post
    hey guys

    my head is wrecked cause i cant figure out what this noise is. firstly the noise seems to happen when the car is warm and very rarely when shes cold. the rasping noise starts approaching 4000rpm and finishes just before 4300rpm approx. the noise only happens in 1st, 2nd and 3rd but mostly second. from inside the car it sounds like the noise is coming from middle front to middle middle area. oh yeah and it only happens under load which makes it even harder to diagnose. if anybody has any ideas please let me know or if you need more info just ask. also check light on maf and knock but im nearly sure its not related and gearbox crunch form 3rd to 4th and 4th to 3rd im thinkin syncro & baulk rings etc so again im nearly sure its not related to this particular noise. any help much appreciated
    im willing to bet you have a cold air intake..or a front mount intercooler..or even a aftermarket ram air intake...in such case im also willing to bet that if you do the maf is not properly alined causing you to either run dangeroulsy lean or dangerously rich..more then likely rich....that would be why the maf is on and also the knock...the reason your getting a knock at 4000 rpm is cause thats when your turbo is forcing massive amounts of air into you engine..now the ecu reads from the maf and adjusts fuel trims to make a "perfect" air fuel ration..if your maf is reading wrong then your computer is virtually flooding your car with fuel that cant burn.causeing the knockbecause unburned fuel is left behind and burning at the wrong time.....which then in return causes your pistons to fight each other...causing the knock and most likely a bent rod and or a spun bearing.....if im wrong and your car is stock then i would hope your using premium fuel...if your using anything else then your problem is the fuel is ignitiong before it gets where it needs to be to combust causing the knock..lower grade fuels (87or 89) have less of a flash point and can ignite before it reaches the combustion camber on a high perforemance car like yours....good luck hope i helped answer your question...and i wouldnt drive it like that you may have already caused major damage and if you didnt you will...if you did spin a bearing you might not hear a loud clanking on your vehicle wrx's are known to spin a bearing and be quiet..then pieces of the bearing go through your oil get caught in the oil supply line filter and whipe out the turbo causing you to have not only a motor rebuild but also a turbo rebuild/replacement...
    New England F4

    feel free to pm me with any questions..

  4. #3
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    thanks for the reply. the whole car is stock apart from the wheels. i have knock sensor that ill be putting in tommorw and i gona swap maf off a mates car to see if that makes a difference. also shes a jap import which is mapped to run on 100ron(i think) and hear in ireland the best we have at the pumps is 95ron(i havent bothered with additives). and yes wont believe this but when my fuel pump went i just put a pump from a 1.5 civic into her. is this a bad idea? thanks for any replys

  5. #4
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    replaced knock and map sensors today and the noise is still the same. im gona put in the proper fuel pump to see if it makes any odds. if not then then ill remove the aux belts and drive it to see if the noise goes. any other ideas would be appreciated.

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