I have a problem with exaust fumes on 1996 Volvo 960

my volvo 6silinders after warmup it gets slugeged and smelly with unburnet exaust fumes, Ireplaced two bad ignitors but the problem remains with a little un known vibrant with the engine?

Asked by for the 1996 Volvo 960
change all spark plugs to premium plugs, upgrade ignition cables or coils to performance type(accel's), upgrade air intake to high air flow type(K&N). TREAT FUEL SYSTEM with stab-bil ethanol cleaner. your cats do not control exhaust burn but act as a filter. use high grade oil. your engine is not burning efficiently.
I've tried most of what you said but still that's not it. thanks
1 more answer , 1 more comment
you may need o2 sensors is check engine light on
no the check engine light is off and I can't find o2 sensor on my car . where is it't location?