'08 engine troubles...

[sweeneyp]

So I got in my car today and started down the road, and noticed something was off.
-First off there was a strong hissing sound that comes from the passenger firewall area when the engine RPM is higher than 2k, and gets progressively louder as it revs higher.
-And speaking of revs, the engine is less willing to rev now, it is much slower getting up there compared to what it used to be. I tried reving it from idle to red line a few times in nuetral and it would get to about 5250'ish rpm, kinda of hang for a second or 2, then sound like it catches a gear gets real loud and shoots to the red line very quickly.
-No CEL or other warnings have come up at all yet (which I think is very odd, considering what is happening)
-took it to the dealership late this afternoon and the service techs took a test drive with me and didn't even notice the hiss (thinking it was normal), but the service manager (before we even left the dealership lot) recognized an unusual sound (he said possibly vacuum leak). But after "tinkering" with it for 2 hours, they had no idea what the problem was and they had to close. They said I could leave it or take it home (they said it wouldn't hurt it) and bring it back in the morning. I needed my car so I'm bringing it back tomorrow morning. They were planning on taking off the belt and testing everything more thoroughly.

And to top it off my power-train warranty ended 3k miles ago

I was wondering if yall have ever had this issue or have any idea as to what it is???

[jeffs3820]

Not a vacuum leak. Vacuum is highest on deceleration when throttle is closed so if it was vacuum it would be non-existent on acceleration and loudest on deceleration with a closed throttle. If the hissing gets louder as the engine revs, look for an exhaust leak from the exhaust manifold or possibly a leak from the intake manifold. Another possibility is a head gasket...not uncommon either. I'm also assuming there isn't an obvious leak from a fuel line...if the dealer looked at it for 2 hours they would be blind to miss that.

Do you hear the hissing when the engine is cold? Is it tied to rpm or vehicle speed?

[sweeneyp]

Originally Posted by jeffs3820

Not a vacuum leak. Vacuum is highest on deceleration when throttle is closed so if it was vacuum it would be non-existent on acceleration and loudest on deceleration with a closed throttle. If the hissing gets louder as the engine revs, look for an exhaust leak from the exhaust manifold or possibly a leak from the intake manifold. Another possibility is a head gasket...not uncommon either. I'm also assuming there isn't an obvious leak from a fuel line...if the dealer looked at it for 2 hours they would be blind to miss that.

Do you hear the hissing when the engine is cold? Is it tied to rpm or vehicle speed?

thanks for the response, its strictly tied to the engine rpm (happening during acceleration, deceleration, and holding RPM in neutral at a stop) from what I can tell. and it comes directly in front of the passenger seat either at the firewall or a little past it. Its coming to the right of the intake manifold, though I do not know if the exhaust manifold/pipes go toward that area of the car.

[valkyrie]

Its possible that is is a restricted converter It is a fairly simple test for the dealer to do. I think cats are covered for 8 years or 80,000 miles
Just a thought.

[MI-Silver-HL]

I have to agree with Jeff3820 in that it's likely an exhaust leak somewhere.

My previous '02 HL started making a noise only on acceleration that sounded like water running through a PVC pipe. Turned out it was just the gasket between the exhaust manifold and exhaust pipe had a small crack in it that would open up when just the right amount of torque was applied creating the noise. It took the mechanic about 5 minutes to diagnose after I went on a test drive with him to show him when and how it happened. Easy fix. Hope yours is as easy.

[sweeneyp]

Well got the HL back from the dealership, ended up being a vacuum line around the passenger firewall that came loose or something (I didn't ask for specifics on which one). They said they re-attached it and and now the hiss/reving symptoms are gone.
Any major repair avoided (thank goodness)
Best part the dealership didn't even charge me to fix it (I am out of warranty too)

[Sky1111]

So glad to hear that everything is OK - and esp. dealing with the dealership was free