The check engine light had previousely been on with the code pulled indicating a bad catylitic converter. One day when I was running late for work and drove fairly fast, I noticed the check engine light turned off by itself and the engine now sounds like crap. I notice the sound gets worse as the rpm's go up and there seems like a significant loss of power. My question is what could be causing this as one 10 minute drive surely couldnt clog up the cat all that much more... especially since it had a bad cat for months... Are there any other potential problems that could have made it sound this bad after one fast drive?

 

It's really hard to say without knowing what it sounds like, can you be more specific? Is it a whine, a clatter, what?

 

Not really a clatter but a deep, bogged down kind of sound you hear with old cars. My old 1986 Camry has a similar sound.. I'm gonna do an oil preasure test soon but I wonder why the check engine light had randomly turned off. Is it possible that the ECU no longer recognizes the cat is bad and has re-adjusted the fuel injectors on account of a false positive ( interpreting a good cat when in fact it's actually bad)

 

What you hearing could be many things. Best thing to do is take it to another mechanic and let him hear it.

Mileage would be helpful but it sounds like your engine is worn.

The reason you're just now hearing it is because the old oil was thicker (It becomes thicker as it ages and gets dirtier)

How often do you get oil changes? If you don't do them as much as you should then you may need a new engine.

The new oil is cleaner and thinner. (Assuming they put in the correct oil) You might want to take it back and ask them to change it again with a heavier oil or try Lucas Oil Stabilizer.

It can be anything from your lifters to a knock, which will progressively get worse.

 

The car has about 330,000 miles. A few mints back I noticed a loss of power and that's when a code was pulled indicating a bad cat. The oil has been changed roughly every 4000 to 7000 miles. However in the time frame that the engine started really sounding bad the oil had not been changed. I question that a 10 minute drive (which I did kind of drive it hard but still) would have such a significant impact on the oil. Also when in first gear and going up a hill, as the rpms climb to 3,000 it sounds one way, then gets significantly worse and sounds louder and worse as the rpms go above 3,000... Maybe it's the vtec kicking in on an already compromised engine? As it climbs to those fear 3,000 rpms the car has a short shake from the engine..... Would a bad cat really cause further damage that lead to this condition?

 

definitely the cat read this...... http://www.ehow.com/how-does_4899113...onverter_.html