my last thought is the metal in the exhaust is system at the block and flange can no longer take the heat so a new thicker metal system has to be fitted
is the catalytic converter clogged or a collapsed muffler ....anywhere in the exhaust have a restriction by the time the gasses reach the tail piipe
your diagnosis of the engine says it is good and not the problem.. only the exhaust
system
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My car goes Brumm Brumm
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