Quote:
Originally Posted by notfarnow
can't wait to hear the experts chime in, I was wondering about this too
My understanding is that the cat doesn't affect *performance* because there is nothing measuring its operation & output. It cleans up the emissions, but doesn't give any feedback into the ECU to affect driveability or power.
The exception is if it's plugged and causing excessive backpressure, but that is a mechanical issue, not a sensor/computer one.
Mind you, this is my understanding based on 10+ yr old cars that I've owned. Probably the newer, more complex cars measure post-cat emissions
|
a properly functioning modern cat has little to no effect on hp, the big thing to understand is that they DON"T wear out..they get destroyed by other upstream issues. They are also often replaced by people who do not understand that a p0420 code for inefficency is not alway a bad cat...alot of times it is a vacuum leak, carbon deposits on the backsides of valves(effects mixture to extreme), a misadjusted throttle..a mad MAF or other things that don't throw a code. Basic diagnostic ability is severly in need these days and many if not most mechanics are just parts changers. I get lots of calls on bad cats..i ask specific pointed questions(i know the answers) and 99.9% of the time these "experts" have no idea what i am talking about.
good example is honda oddessy. these are NOTORIOUS for bad cats...and they eat oem/aftermarket ones up it seems. well if the mechanics go only by the obd codes, they are treating the symptoms...not curing the disease. The problem is plugged egr ports, there is no code for this as it is only a code for open or malfunctioning egr valve...not for low flow(the code says low flow when it is stuck shut...but never if it actually opens and closes fine btw) but almost all mechanics will condem a cat and not think to diagnosis this. Most "techs" don't even know that if you run the cat monitor, and it passes, the cat is good and the problem lies elsewhere.
A GOOD tech will diagnose the problem in conjunction with scanning codes..not just to charge extra, but to ensure that the correct repair is done
a very good tech article on cats is on troublecodes.net