4.8is With Hissing Sound
 

Hi Guys,

Of late, my x5 has developed this hissing sound from the left side of the motor on startups. The hissing only occur for about 45 seconds to 1 minute. I dont know if this is weather related because it has been cold in CT. I cleaned the airfilter and checked the air intake system and could find any air leaks. So, last night I removed the engine cover and I could hear the hissing sound from the top left side of the engine. I have searched this forum and gogled but could not find and resolution. Any input and advice would be appreciated.

any loss of performance, or fuel economy? any blue, white smokes from tails? do you have diag software that you can connect to the car? it might be running too rich, too lean but not set off the engine check light (yet) and still have a code in the system...

I have not noticed any loss in performance or gas mileage. Unfortunately, I do not have any diagnostic tool to scan for codes. Never got any Engine Lights.

hmmmm... are there any vacuum lines that you could see? hissing sound would suggest air being siphoned... but, no loss of performance?...

lets if anyone else can chime in...

One would think if it were a vacuum leak somewhere, you would get some lights or definitely notice it running a bit odd.

Got a smartphone? Take a short clip and throw it up on YouTube for us to hear...may give us some insight as to what it could be!

Your assessment of the situation is the same as mine. I could hear but could not narrow down the location. I could hear it coming from the top of the engine. After removing the engine cover I clearly hear where the hissing sound was generating. But, I could not remove that long black rectangular cover to have full access to the hissing sound. It appears thag rectangular box covers all sorts of wiring. May just need to take a ride to my friend's shop to have all the proper tools to work.

could it be not air hissing sound but a metal part "dry-running" on other metal (or plastic) part? does the pitch change with the engine RPMs?

That's was my first assessment. But, could a vaccumm leak that high and far up inside the engine bay. The hissing sound is nowhere near the intake system. I have trying to get this resolved and really frustraded. Other than that, the x5 has been a great winter replacement while my M5 hibernate during the winter months.

I know for sure its not metal rubbing sounds. Like said, the hissing sounds only lasted for about 45 seconds to 1 minute; each hissing sound intervals would be maybe 5-10 seconds apart.

Check the vacuum tube coming off the pipe between throttle body and MAF. Mine had decayed. No more hissing sound from mine.