Hello. I've had my 76 Cadillac Sedan DeVille 500 ci since new and it's been
well cared for. In recent years it's developed an exhaust noise no one has been
able to figure out.
When idling in neutral, running up the engine to about 800 RPM produces a deep
roar. The same sound occurs while driving at a steady speed with just moderate
pressure on the accelerator. When taking your foot off the accelerator while
moving, there is a sputtering roar (just like a bad muffler sounds). Also, when
stopped in neutral, revving up the engine and quickly taking your foot off the
pedal produces the sputtering roar.
The exhaust system (all Walker parts) is new from the outlet of the converter
back. The sound comes from the muffler (and out the end of the tailpipe),
checked with stethoscope to be certain. There is no indication of leakage
anywhere in the system. We replaced the new muffler just to be certain there
was nothing internal in it causing the problem. The catalytic converter is the
original one and the heat shield has some rust holes in it, but no sound coming
from it. New plugs, rotor, cap, vacuum advance, vacuum hoses, timing carefully
set (6 BTDC at less than 600 RPM). The original type converter is not available
and I question if the small replacement ones would be satisfactory. I can get a
rebuilt one, but haven't been able to find one without holes in it.
Any thoughts on dealing with this very annoying situation?