When i accelerate i hear a hissing noise (best way to describe it) coming from the dash board but i was told it was an exhaust leak... there is a noise coming from the back of the motor in which they say it is that but to me that doesn't seem right... could it be something else? maybe a gasket bad or something... it only makes that noise when im accelerating or if they car is idling if u listen really really really closely on the inside u can hear it but under the hood the noise from the back of the motor i know is not normal but i wanted to ask first.

There are some vacuum lines under the dash to control the HVAC system. Check those.

Who told you of this exhaust leak? If it'* a mechanic, I'm inclined to believe them and would be checking the O2 sensor in the manifold. I've seen them loosen up and cause leaks. Very easy and quick to fix.

What if he were to try Seafoam in the top end (brake booster vac line) and watch the engine bay and under the car for smoke?

Any seafoam treatment on the top end would blow smoke out of any leak.

Tony, if you are having a difficulty time locating the leak you can use a vacuum port to suck some Seafoam into the intake manifold. It will give the top end a good cleaning, but it will also smoke the exhaust like a son of a gun. You will be able to see any exhaust leaks.

Do a search on the Bonneville Forum for Seafoam, and/or ask us if you need help.

okay ill try that thank you all for helping

Let us know what happens.