Young Chuck D

i changed the air filter, pcv valve, spark plugs, oil, oil filter... all these after the first test, however today i failed again in the same categories: Hydrocarbons and Oxides of Nitrogen. What should my next step be? somebody save me before i go to the chevy dealership and get gouged.

once again, 1989 Chevy Cavalier 4 CYL, 2DR coupe.

cdru

High HC means high amounts of unburnt fuel. This can be from a faulty plug, wire, ignition coil, poor cylinder compression, faulty injectors...

High NOX can also mean that your timing is set too far in advanced (if you can even adjust it), your EGR isn't working properly, vacuum leak, etc...

Your cat could also be poisoned and no longer functioning correctly.

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Vinyl adds horsepower, right?

Young Chuck D

ahh the treacherous catalytic converter.

whats an EGR....?

if i have all of the above fixed/replaced, what should it run me?

cdru

Sorry, I left off the valve portion of EGR valve. It recycles a portion of the exhaust gas back into the combustion chamber. It robs the system of a little bit of power but is suppose to make it burn cleaner.

The cat will be around 60-75 probably for a generic "universal" aftermarket. If you want a better cat such as a high flow or performance, it will probably be closer to $100+. If you want to install it right, you'll want to weld it on. I just replaced one in my minivan and it was $50 to remove/install/weld it at a local shop. Or you might be able to use clamps at a couple of bucks a piece.

The EGR is also probably around $60. Don't forget the gaskets. They usually aren't too hard to replace...if they are accessable. Not sure on your engine. It's usually a couple of bolts holding it on to the intake manifold.

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Vinyl adds horsepower, right?

Young Chuck D

thanks.... is a catalytic converter do-it-yourselfable? i'd rather buy a repair manual than get robbed at an auto shop.

and that EGR valve too...?

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1996 Oldsmobile Cutlass Supreme SL Coupe
formerly employed by:
1990 Hyundai Excel GL
1989 Chevrolet Cavalier Coupe
1998 BMW M3 Hardtop Convertible

alpurl

If you have the same engine that I do in my 88 sedan, 2.0 4 cylinder, then the EGR valve is a piece of cake. A 13 mm wrench will remove the 2 nuts holding the EGR valve down, and then the valve will lift right off.

The EGR valve is located at the end of the cylinder head at the rear of the engine, this is the end on the driver's side of the car.

If you wanna know what the EGR valve looks like and how to test it, check out this ten mile long link.
http://www.autozone.com/servlet/UiBr...3d800f00fd.jsp

The cat is a wee bit of a different story. As I understand it, the cats are supposed to be welded in according to law. If this is indeed the case, then you'll have to physically cut the cat out with either a die grinder or saw, or you'll have to use an oxy-acetylene torch. After that, the new cat should be welded in.

If it makes you feel better, I've been chasing some gremlins of my own. The car has not passed emissions since I first came into possession of it. It also has a knock at high rpm that sounds very much like a rod knock.

I've had to replace the ECM and the O2 sensor.

Under the advice of one of the commercial sales reps of my local Autozone, he suggested that the knock was the result of a bad cat.

I managed to borrow a full scanner from my stepdad, and found the knock to occur when the ignition timing nears full advance starting at 49 and going to 53 degrees.

As far as I can tell, the O2 sensor and all of the rest of the system are functioning properly.

Had the car checked today, and the HC emissions were 137 ppm which is passing, the CO, while I don't remember the value, was passing. The NOx emissions were another story. While I don't know what "PASS" is, the output levels were in excess of 1300 ppm, as far as I know, this falls into the category of gross polluter.

I had my catalytic converter tested yesterday via the temperature method. The temperature should be higher coming out of the cat than going into it. In 3 readings over 3 minutes, the temperature difference had the output cooler by anywhere from 34 to 47 degrees.

So, now I've got to check my egr valve to make sure it's working properly first. Somehow, I'm not quite sure that it is.

Why would the emissions tech suggest that I replace the O2 sensor again? I just don't see how an O2 sensor could affect NOx emissions.

alpurl

Ok folks, here's the situation...

I've put a vacuum pump on my EGR valve, and pulled the lever.

Not only is it NOT responding to vacuum, it's NOT EVEN HOLDING VACUUM. That explains the ridiculously high NOx emissions.

So, now I'm gonna replace the EGR Valve and take it through emissions and see what happens. The way I see it, worst-case scenario is that it'll bring the nox down, but not quite enough to pass. At that time, then I'll have to replace the cat. It'll definitely pass after that.