Catalytic converter?
 

My '96 Nissan Maxima (3L V6, 4-door sedan) has been making a high-pitched sound and recently the emission control warning light came on. I took it to a shop and they said they need to replace the "tensioner pulley" and the "catalytic converter" (I got these over the phone so I'm not sure about the spelling). They said replacing these will come to about $1400. The pulley, whatever it is, is about 250 for part and labor, but the catalytic converter will be 1000+.

What exactly is the catalytic converter? Can it not be replaced and the car still be functional and whatnot? I'm not familiar with English terms for car parts. It sounds a bit like what in Finnish is called "katalysaattori" which essentially "cleans up" exhaust emissions in three different ways. In Finland these were very expensive when they first came out, and a lot of people either took theirs out and resold or simply didn't replace a malfunctioning one due to the high price and a myth that the part caused engines to give poorer gas mileage and engine power. That of course was illegal in EU countries as of the early 90's. I don't know about the States, or if this is even the same part.

How essential is this converter? The repairs would come to about 1400 and I don't know if this car is even worth that much.

Your catalytic converter looks just like the muffler. It's located before the muffler. And yes, you have to have it. It's illegal to remove it. The cliff notes version is that they convert harmful gases produced by your engine (carbon monoxide) into CO2 and hydrocarbons to water and CO2 (carbon dioxide). It's a lot more complicated than that, but I'm sure this is enough to make you realize how important Catalytic converters are for the environment.

Were you having any other issues than the light coming on? And 250 for parts and labor for the the tensioner pulley is pretty steep. Can you do the work yourself? I replaced mine recently ('94 Buick LeSabre) and it took me 15 minutes.

apparently there's some rare metal in the catalytic converter that makes that cost so expensive. theft of them is on the rise from what I understand and based on some cousins getting their stolen last month.

There sure is. Platinum is the most common.

Yup. Platinum. Lots of it, too.

catco.com has them for about 100 bucks, which is usually cheaper than the mechanic will sell it to you for.

That said, the high pitched sound could be an over-tightened belt that's pulling on the alternator pulley too hard. It may be that you don't have to replace the tensioner pulley - you might just have to re-tighten it to specs. It's not unusual for a mechanic to claim that a part that only needs adjustment actually needs to be replaced, because they can make more money that way. I'd get a second opinion.

Some information on the amount of platinum in your catalytic converter...

LINK

For everyday operation, not essential. If you want your check engine light to clear and pass your annual emissions inspection (provided your state has one), very essential. With newer cars (manufactured in 1996 and later) they were equipped with two oxygen sensors, one before the converter, and one after it. The first sensor works like any other oxygen sensor, monitoring the air/fuel ratio and making sure the mixture is optimal. The second sensor is used by the ecu to make sure the converter is actually working by comparing its signal output against the output of the first sensor. If the signal between the two sensors are a close match, then the ecu will assume that the catalytic converter is no longer operating and that is why your check engine light was triggered.

I will have to disagree with you on some of your information. The catalytic converter is very important for every day operation, especially depending on what has actually failed. If the catalyst has melted, it will develop a restriction, that will cause excessive back-pressure in the exhaust system, resulting in severe power loss, and or excessive heat in the engine. Long term results could include major engine damage if the catalytic converter is not replaced.

As far as the pre-cat and post-cat sensors, you are right about the pre-cat sensor monitoring the oxygen content of the exhaust as it exits the manifold, and enters the exhaust stream. By measuring the oxygen content, the PCM can calculate how efficiently the engine is operating as far as air-fuel ratio. However the post-cat sensor also reads oxygen content coming out of the converter, thus measuring the efficiency of the catalyst, and its ability to store unburned hydrocarbons and convert it to the inert gasses for the exhaust. Oxygen sensors are just that, all they do is measure how much oxygen is in the gasses flowing past it. It can't measure anything else.

i think what was meant was "what would happen if I took out the cat and put a test pipe in instead," in which case, as far as the car's operations go, it won't hurt anything. But, it will belch a lot of nasty crap into the environment.

That also depends on the age of the car, early catalytic converters were mostly publishitystunts as they changed the polution but didn't actually lessen the impact to the enviroment.
I had a truck that had the cat replaced with smooth pipe and I belive that was an over all improvement and "green" modification since I got more miles per gallon.

Yours
ZB

+1 on a second opinion.

If your belt is just too tight or worn causing this noise, and you are a little bit mechanically inclined, you can save some bucks. And if there is an Autozone near LV-426 you can have them read the codes that are causing your CEL. You may very well need an oxygen sensor instead of a catalytic converter.

Quoted for truth! good point Psycho Dad!

I got the cat replaced at a local muffler shop, parts and labor set me back a bit over a hundred. The tensioner pulley was also replace. The engine runs quieter now, BUT...

When I took the Maxima in I told the mechanic that the car makes a high-pitched noise very often. It only makes the noise once I’ve driven it for a while (all warmed up I guess) AND I have my foot off the gas. For example, when I come to a red light, or am sitting in a drive-through line. Since the sound is pretty annoying (it’s loud, but it’s the high frequency of it that makes it more embarrassing) I usually try to get rid of it by putting the car in Park, which sometimes helps, sometimes makes no difference. If I apply even the tiniest bit of gas, so the RPM goes up, the noise stops instantly, to return again when the RPM drops to normal idle values. The engine usually idles at around 500-600 RPM.

Well the mechanic heard the sound because it was making it when I took it to the first place but he said to me that it was “probably just that truck driving by making the noise, its brakes or something.” While the new pulley and the cat have made the engine run otherwise nicely, this mysterious sound still persists. It is difficult to demonstrate the sound on cue so I ran the car for an hour and taped it once it started making the noise again. Unfortunately it was only making it when the car was in Drive so I had to just video the engine from afar and not up close – since I was by myself.

I would appreciate it if you could please take a look at the clip at and let me know if it sounds like anything you’ve heard before.

Personally to me it sounds like a ported vacuum leak. which will go away when you accelerate. But since I don't know Nissan that much, I cant swear to it.