I was OK on NO, but way high on CO and HCs. I believe the CAT oxidizes CO to CO2 and HCs to CO2 and H2O.

So, I'll take a chance and get a CAT. From a performance point of view, what's a good CAT?

 

Brand isns't that important. Just don't buy the cheapest thing available. Don't buy a universal unit. A good 3 way oversized cat will probably cost you between 150-250 dollars... not cheap, but you'll never have to worry about it again.


Rod.

 

Rod, are my readings in post #26 indicative of a bad CAT?

Thanks,
John

 

OK, a few things here. I am a licensed smog tech so i my have a little more useful info for you.

The oxygen sensor is a good place to start but it is not the only sensor that effects fuel ratio. You also need to test the temp sensor, the MAF sensor and possibly fuel pessure.

Also, on almost every o2 sensor I have ever tested 450mv is considered dead even fuel mixture so 400mv should not be enough to couse a rich condition. And also the sensor should actually be switching between 200mv and 800mv so a DVOM isn't the best tool to test with but it's better than nothing.

If the new sensor doesn't fix the problem try some of these other possibilities. good luck.

 

Thanks guys. I'll let you know if I pass smog after the new CAT. Spark plug color is good now that I have some miles with the new O2 sensor. ZBob - the DVM seems to be trying to indicate the range you specified. It might be a week or so before I replace the CAT (been off work 7 weeks from the valve job on my ticker) and also have to replace the down tube because some ****** welded it to the old CAT. The bloody down tube lists for $112 at Autozone. Unbelievable!

Once again, thanks to all
John

 

Find yourself a good exhaust shop and just let them make you one. It's gonna be cheaper than buying OEM type replacement pipes. There's a lot pf good exhaust guys out there that will replace everything from the collector back for a couple a bills. On Zbob's post: what he says is true, However, most of it doesn't apply to your car. The only thing you've got is an o2 sensor and a limited computer to adjust mixture. All that other stuff was still in the future in 1981. But he is right in what he said. I guess a weak fuel pump or bad pressure regulator would cause a mixture based smog failure, so he's right about that too.


Rod.

 

The only problem is that his mixutre isn't off. So the problem most likely is the cat. If the O2 is switching then we know it's working. And since it's reading within specs then it's most likely not a faulty sensor. Plus it's a new sensor. I know they can come bad but considering everything I said above I would think the O2 sensor is functioning properly. With that being said, it can't be a rich/lean condition with those O2 readings. That to me definitely smells like the cat. So it looks like Rod was right all along

 

I get one every now and then.

Rod.