Dear Jim,

My 1998 Toyota Camry has been losing power lately, especially when I'm going up any kind of hill. I did take the car in to a mechanic and he said he didn't see anything obvious right away, but that the problem might be in the catalytic converter. Does that make any sense, Jim? I know the catalytic converter just removes chemicals from the exhaust, so why would a bad one cause the engine to lose power? Anyway, the problem seems like it's getting worse, but I don't want to pay for a new converter if that's not going to fix this.

-- Jordan R. Demaris

You're right, bro, the catalytic converter's job is to cut down on toxic emissions, but this mechanic could also be dead-on with his diagnosis. What he means is you might have a partially plugged converter, and that's what's causing the lack of power. When these things fail, it's usually because they're partially or completely blocked inside, and it's easy to explain how this happens.

Inside the catalytic converter is a ceramic honeycomb material that's coated with a precious metal catalyst, usually platinum. As engine exhaust flows through the honeycomb, toxic byproducts such as carbon monoxide, nitrogen oxides and uncombusted hydrocarbons chemically react with the catalyst, which breaks them down into nontoxic replacements.

To work at all, catalytic converters need to be hot, but not too hot. If too much unburned fuel from the engine is fed into the exhaust, it ends up igniting in the unit itself, and the intense heat from this can actually melt the ceramic honeycomb inside. That's bad.

When the honeycomb starts falling apart, it can easily clog the exhaust path, creating so much back pressure in the system that the engine can't run efficiently, and that may well be what's happening here.

Remember, though, brother, that even if the converter has been destroyed like this, it didn't get that way by itself. Too much unburned fuel coming from the engine can be caused by several things, including a single misfiring spark plug, bad plug wire, faulty oxygen sensor or a leaky exhaust valve.

Have these things checked and get the real problem isolated and fixed before putting in a new catalytic converter. Otherwise, the underlying cause of that meltdown won't go away. You'd just be setting up a brand new unit for the same ugly fate, and that would be money down the drain.

Buffalo Jim, owner of Allstate Auto & Marine Repair in Las Vegas, writes a weekly column. Send your automotive questions to him at buffalojim@lasvegasniftynickel.com. If Jim picks your question to answer in Nuts & Bolts, you'll also be the proud recipient of a deck of official Buffalo Jim playing cards, presented in a classy, tin box bearing his hairy image.