Soooo... pretty sure I have a manifold leak and you guys can say yay or nay. My plan is to remove it this weekend and figure out what's going on. 3 things going on and my hunch is that they're related... At idle it's almost sounding like a disel, lol. 2nd is that I notice a power loss and 3, if I really stand on it at the hwy... I get exhaust fumes in the car. Ideas? Thank you!!

 

If you are leaking exhaust from somewhere it's usually pretty obvious where it's coming from.

If you think it's from the exhaust manifold, pop the hood and stick your head in the back and listen. Or feel, don't touch it of course, but if exhaust is coming out you will be able to feel it blowing on your hand.

If it's not the manifold you'll need to jack up the car. Use jack stands! Do the same thing. Start it up and listen.

It sounds like you have a couple issues actually. Since you are smelling exhaust in the car it must be leaking from somewhere. But the lack of power and diesel sounding engine aren't necessarily related.

An exhaust leak that small wont make you lose that much power. A leak doesn't really make the engine sound like a diesel either.

It's a different kind of sound and with the exhaust manifold all the way in the back you can hear the difference between a leak and an engine sound.

 

a large hole in the exhaust manifold will be loud, and have a noticeable difference in sound especially with a stock exhaust. wether or not it will sound like a diesel is all in preference and perception, ticking is a sound that a cracked header will not give however, unless the crack is on a joint and its consistently moving.


a loss in power would be because you have an engine code and the ecu is trying compensate since it will see more air going by the 02 sensor and adding more fuel. (you will have a SEL light)


exhaust in the cabin would really be from anywhere in the system. I have no leaks, but when I come to a light with the windows down I can smell mine. if your windows are up and its coming in the cabin that's a different story

 

Small leaks from the header being cracked can transpose themselves as a tick, or putter at idle, or if you're lucky enough the back half of the header just falls off and you sound like a back country boy in a jacked up Chevy until you fix it.

If the leak is bad enough you would have a loss of back pressure, which could cause a loss of low end torque, but not loss of power across the rev range.