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Mack 300+ ETAZ upper rpm exhaust fluttering noise


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Mack 300+ ETAZB673A on A RS600L '77.

Just experienced an upper RPM 1600-2000 exhaust fluttering noise when into the pedal. The exhaust is also black where it is normally clear when in that RPM band when loaded. Otherwise idles great and no other symptoms. Seems to also be intermittant.

Is this the symtom of a fuel filter just getting plugged at higher fuel flow?? Injector pump getting starved?

bad Injector?

valvetrain issue?


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had alook this morn... turned out to be a leaking #6 exhaust manifold. Just a slight leak until the pressure climbed up. The valve cover gasket that leaks a little masked the telltale soot indicators.

By the way, it seems difficult to seal these valve covers. New gasket and it still leaks. Heard you just have to get it on the 'sweet spot.'

Thanks again.

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