awilli6

87 S4 driving home and running fine. Suddenly, down on power & I smell something. Not oil or antifreeze. Pull over & catalytic converter glowing red hot. Car is running like it did when 14 pin got wet. It's raining here so maybe that's it. I was crawling through traffic when power went down. I have been having issues with it being harder to crank. It also ran rough (like every couple of seconds someone was bumping the car in the engine compartment. Would smooth out in about 5 -10 min

Adamant1971

Clogged Cat

awilli6

How do I unclog it & what could be clogging it?

John Speake

I suspect an ignition problem, letting unburnt fuel from non-firing cylinders pass into the cat that side. That then gets ignited by the hot gases from firing cylinders.

Do a full check on coil wires, plug wires, distributors etc...

17prospective buyer

When you drive running excessively rich for a long period of time will overheat the cat and it probably got hot enough to melt the internal waffle substrate. See how the plugs look.

Kevin in Atlanta

IMO

Not a clogged cat - likely you are running on 4 cylinders and pouring raw gas into the cats. Do not drive it until you verify you are running all cylinders. Worst scenario is you could burn your car to the ground.

ammonman

Sounds like one side of the ignition may have quit so you are running on four cylinders. The fuel/air mix being injected into the four non-firing cylinders is being expelled out the exhaust and catching fire inside the hot catalytic converter. Check and see if you have spark from each of the coils to the respective distributor cap. The rain may be coincidental, but it could be that water has got on one of the ignition coils and shorted it out. Check all the coil leads (primary and both secondary) for secure attachment and corrosion. Be sure the protective caps are in place on both coils to help keep the terminals dry.

Mike

awilli6

Thanks. Waiting on AAA and phone battery is low. Will check back when I get home

karl ruiter

Yes, ignition problem with unburned fuel going into the cat. Been there. Plug wire in my case.

Randy V

This.

The cause of many a 928 carbeque.

Wisconsin Joe

Rain/Wet/Damp has a tendency to make marginal ignition components inoperable. The moisture conducts the electricity through cracks and "bad spots" and keeps the plugs from firing.
That's why the "Firefly Check" is often made more obvious by spraying water on the distributor and wires.

awilli6

Thanks for the info guys. I'll check this Monday. I have to work all weekend

AO

Yep! This.

Check your coils, coil wires, caps, rotors.

James Bailey

if you have an inductive pickup timing light or borrow one just check plug wires...two on each bank are probably not sparking. Trace back to which coil and look for corrosion.

fraggle

Failed coil, rotor or primary wire.