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Since I bought the car there has been an audible fluttery sounding exhaust leak coming from the back side of the engine or under the car.

I'm ordering a ZZP downpipe soon, but I am assuming this exhaust leak is only the gasket where the exhaust manifold attaches to the exhaust pipe, as the leak is only heard under load.

If the manifold was cracked or leaking, if I'm correct, you would hear a constant ticking even at idle.

I just don't want to pull apart the exhaust and replace the gasket or install the downpipe and then find out it's the manifold, or replace the manifold and find out it was only a gasket. Haven't had a chance to be under the car to listen or look for the leak, but you can hear it only under acceleration or load applied. Probably just typing this out to verify my throught process lol.

On a side note, have any of you used the ZZP downpipe? I'm going to be ordering that, with the front power log and the ported throttle body.

assume nothing - get it up on stands and you may find the heatshield loose and rattling - see if you can recreate the noise with a helper holding revs

Got all up in there. Leaned over the back of the motor and revved it. Can definetly hear the flutter coming from the gasket. You can see the gasket looks like it’s starting to fall apart on the top and that’s where you can clearly hear the leak. Problem solved. Now to spend money to repair lol. Going to be putting my ZZP order in within the next couple weeks.

Just spent my ZZP savings on a new fuel pump, EGR valve and fuel line repair on my new LeSabre. But that’s dealt with now.

so its the doughnut gasket where the downpipe meets the intermediate pipe? you can replace that yourself: not very hard 4 bolts iirc - rust is the enemy