Hissing noise from motor at 5000+ RPM

94325is · 11-23-2003, 12:07 AM

everytime i get on it hard i hear a hissing almost like a cross between a belt squeal or a vacumn leak. i have replaced both belts and so i know thats not the problem but it comes durring hard acceleration at about 5000+ rpm anyone experienced this ohh and i have checked all the vac hoses and have found nothing i am thinking of replacing all of them just for the hell of it cause some are oil soaked and may be leaking but not at idle?? plus its inexpensive and about time with 117xxx

Wayne 962 · Wayne 962's Garage

Hmm, is this speed independent as well?

-Wayne

94325is · 11-23-2003, 08:39 AM

speed? you mean does it happen more at a certain speed or certain RPM. it happens in all gears but when im in 4th and 5th it just not as notice able cause im not at that high of an RPM in these gears but it does occur in 1 2 3 i know cause i can hear it over the wind noise with the windows down, i haven noticed a lack of power really if anything "maybe" a little lack of launch.

Wayne 962 · Wayne 962's Garage

Does it occur if the car is not moving (rev it up to 5000 and listen - it won't hurt your engine, although it will sound really loud)...

-Wayne

94325is · 11-23-2003, 05:58 PM

no its only when i am moving which makes me think it is like a vac line or something i did replace the 2 hoses going to the pcv valve if thats what you wanna call it and cleaned that all out with an intake cleaner spray and it seems to run a lil smoother and just sounds a little cleaner but i also sprayed the intake cleaner in the icv and all throughout the throttle body and intake runners havent had a real chance to get ON it cause it has raind all day but i will post tomarrow with some results of a WOT test ha ha well ttyl thanks -Jon ohh and im going to try to replace a few more vac hoses also gotta dig though

Wayne 962 · Wayne 962's Garage

Could it be a belt noise?

-Wayne

94325is · 11-23-2003, 10:08 PM

well i was thinking that also but i just replaced both belts to fix a belt squeal at idle and it did work for that cause it i quiet at idle now but still hisses at high RPM i heard that there was a service bullitan on the belt compounds used and some were noisier than others so i was wondering if anyone has used a gator belt on their BMW to reduce noise cause i bet it would work and its worth a try for about 20.00 but id like to single that out befor i go through that labor again??

94325is · 11-24-2003, 08:57 PM

OK finally success the hissing has been lessend by puting a new O ring on the PCV orfice in the valve cover. also i noticed it runs smoother and i had an idle bounce every now and then and its gone too the idle bounce was between 500-800 RPM not bad but was noticable anyway i thind the intake cleaner solved that but im still diggin and looking for the rest of the hissing let me know if anyone solves this befor i do -Jon

Jared at Pelican Parts · 11-25-2003, 04:19 PM

You may want to consider replacing all the vacuum hoses. Chances are, they have never been replaced and you have a significant leak in the system somewhere.

94325is · 11-26-2003, 04:57 AM

yeah thats what i am in the process of doing but you dont have a vacumn diagram for a 94 325is cause the only lines i found were the big and the little one that go up to the PCV orfice there is a huge hose that goes from the ICV to the intake but thats gonna have to be a BMW part not just a vac line but if you know of any others that are hiding down there let me know -Jon