What's burning my...?

Something is causing the Catalytic Converter to burn up on my '99 Chevy Venture mini-van. Three different repair shops, including the dealer, have just wanted to replace the coverter without finding out what is really causing the problem. Any ideas?

Check engine lights on? What codes?

And what specific codes? We need the real code in the format [P1234] Not just the human language.

If your catalytic converter is burning up your minivan, I would look for a missing heat shield. Replacing it should keep your minivan from burning up.

I assume by “burn up” you mean that the catalytic converters are overheating, melting internally, plugging up, and/or breaking up. The cause of this is unburned mixture i.e. air and fuel, getting to the cat via the exhaust header. The most likely cause is a high speed missfire (you probably would notice a low speed miss). Less likely causes are a burnt exhaust valve or poor compression in a cylinder(s).

A cylinder miss will usually set a DTC code which should be stored if the Check Engine Light is ‘ON’. I cannot imagine that the dealer would not have scanned the ECM for codes so you may have a true mystery on your hands.

Hope this helps.

Why do you feel the CAT is “burning up”???

Define “burn up”. The melting temperature of the platinum-palladium is about 3000F, the cermaic even higher. I can guarantee your cat converter is not getting that hot.

There are, however, ways in which a converter failure code can be caused by an engine. One is that the downstream oxygen sensor can get coated with exhaust residue, typically either carbon or oil fumes. In really bad cases of prolonged oil burning the catalyst itself, the platinum-palladium, can get coated and lose its effectiveness. And the third is if a cylinder problem causes an overheated spot in a portion of the ceramic substrate, it can fracture, break apart, and restrict flow. This is not a common condition, but it can happen.

Exactly what’s been happening with your car?

We need more information.

How many miles are on the van?
What type of gas mileage are you getting in it lately?
How much oil do you go through between oil changes, and how long is your oil change interval?

There are several causes for converters that go bad.

First off is an engine that is spewing raw, unburned fuel into the exhaust system.
Many causes, cylinder misfire, bad MAF sensor, fouled spark plug, etc.

Next is oil contamination of the converter.
Faulty EGR system, faulty PCV system, worn oil control and piston rings, too much MMO in the fuel mixture.

Are they just getting a check engine code that says the converter is bad, or have you had an emissions test that is showing that your van is polluting too much?