Hi all, I've just noticed the exhaust note on my 355 has become very flat between 1000 to 4000rpm. It has lost that deep rumbling sound, it becomes normal after 4000rpm. Also associated with the note change is a mild vibration I can feel through the drivers seat. At my last service they advised me that a Cat would require changing in the next six months, would this cause it?? I thought that one of the connections could also be loose. I have searched threw previous posts and can't seem to find any details on this problem. Any thoughts would be appreciated!
Several possible root causes, difficult to tell on the basis of your "flat" exhaust note description. If you're getting a greasy, gargling note instead of the neat feline howl of the 355 at 3500rpm, then you might have made it to manifold "heaven" (http://ferrarichat.com/forum/showthread.php?t=17439). Can you hear a pffft leak noise when the car is cold ? Otherwise, could be the bypass valve being stuck, but this does not match your description. Stuck open it would be louder at low revs. Stuck closed, it would be quieter at higher revs. Finally a cat, but I have no clue what the exhaust note impact is (I can guess that the wallet impact is significant). No clue either about this vibration you refer to, but I would not leave that to chance.
If you have vibration (like a rear wheel out of balance?) and a changed exhaust note i would bet money on a Cat failure and the bits left are blocking (or partially blocking) the exhaust on that bank. At higher revs the exhaust is directed away from the lower two cats (one for each bank) hence it appearing Ok at higher revs Look for white powder in the exhaust tails , this will also confirm a Cat failure been there , seen it, paid the bill
Please report back on your findings...it is always helpful to hear the results on this list. Thanks, Dave
Hi all, Took the car too the shop expecting to have the cats replaced, however was pleasantly surprised. The problem turned out to be a loose air filter box, the two rubber bushes that hold the box had split. This was causing the vibration. The exhaust note change that i noticed, was really a change in the induction noise below 4000rpm. Cheap easy fix this time. Thanks all for the advice. Happy holidays!!
