[brider]

Now that I've had my size/shape cat question answered, here's the last one: Can damaged or old/worn-out cats cause an engine to run roughly, or stall completely, or give off BAD smells (propane-ish)?

I'm tempted to let my cat problem (seriously annoying rattling) go until I have time/$$ to deal with it, but in the meantime I have an intermittent stalling problem accompanied by an overpowering fuel smell that I now think MAY be caused by the bad cats. Truck will stall sometimes in a parking lot, sometimes while driving 65 mph down the road. In all cases there is an awful smell that's ALMOST like raw gas, but really more propane-ish. Wait 30 sec (or sometimes less), and it fires right up and runs like there's nothing wrong.

Wondering now if the cat internals are so rotted and broken up (previous issue with mis-firing, which I've learned can destroy a cat) that they can BLOCK exhaust until the engine stalls.

"Besifes" is a new word I invented that means "Besides".

 

[johnthebartender]

Yes cats can cause running problems. Excessive back pressure can cause lots of issues. Having said that, I have to say your problem sounds like one I had in my 94, and it turned out to be a faulty mass air flow sensor. Is it setting codes?

 

[brider]

No codes.

A while back I was having issues that ultimately turned out to be my ignition module (I swapped to the GM remote unit), so I swapped in a MAF sensor from a '95 4.2 that purred like a kitten and showed no weird symptoms at all. It made no difference, my problem at the time kept happening.

I guess that doesn't mean my MAF isn't bad NOW, but I KNOW my cats are bad. Guess I better swap them out pretty quick

Thanks!

 

[cap-pig]

I drove around for about a year with rattly cats and nothing bad ever happened.

However, I experienced the symptoms you're describing in a Chevy truck once. It wasn't mine- it was a company car. One day, it just shut off on the freeway. The cat had become completely clogged and it stalled the engine out. A shop replaced the cat and the truck lasted a few more months after that.

But your description makes me think that there's an issue with the ignition system of your truck that's causing it to dump raw fuel into the cats until they heat up and smell bad. I had a Crown Victoria do that once- it had a few bad coil packs and was literally dumping raw gas out the exhaust. The cats got RED HOT and actually melted the heat shields off the bottom of the car. After I replaced the coil packs, this never happened again. I was sure the cats would eventually go bad, but they were still working fine when I sold the car.

If you are experiencing stalling problems, I'd thoroughly check your ignition system out- timing, coil, distributor cap, rotor, plugs... and fix anything that's wrong. Also check the temperature sensor - the one that reports the temp to the ECU. It has caused serious issues with my fuel system more than once.