i just finished doing a head gasket job on the car. and i put a new intake manifold gasket etc. now when i took of the head i took it off with the exaust manifold. i took disconected the exaust manifold where the four pipes become two. and i didn't replace the two O ring gaskets.
now after installing it and driveing it i get this vibration at the gas pedale when its 2500 rpms. and i hear a noise like the mufler is bad. where does this comes from. does this come from the O rings or did i had to take to change the exaust manifold gasket too????
the reason i ask is because when i did this job 2 years ago and i installed the two O rings the car still did the same noise.

so anyone did this kind of job and had the same problem???? how did u fix it????
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