So it's smog time again this year, and 2 years ago the truck just barely squeaked by. I borrowed my friend's IR thermometer gun to check the catalytic converter.

As I understand it, there's supposed to be a significant difference in temperature between inlet and outlet (which there was). The inlet was running 3-400? and the outlet was running 5-600?. From what I've read, that means the cat is still working fine, but I have to wonder if that's true. It's 23 years old and has been through some rich/lean conditions with all my tinkering with the carburetor. Is there any chance it's bad but still giving a good temperature increase?

I know it's not going to run quite as cleanly as it's supposed to, given the age, mileage, and the fact that I have one of Ted's heads with a 268 cam, but I'm kind of worried about passing this timeà

Just became a member of the infamous CA. "gross polluter" club myself which means I now get to be smogged Every year - not just every other. My 85' has a very low mileage 22r and something wasn't right. I normally do a major tune up before the test but given the low miles just did the basics.

Somehow I missed the very minor leak in the Vac advance. It was the housing leaking not a blown diphragm.

Then I noticed that the exhaust temp was low. Felt low , didn't measure it. Cat wasn't catalysing which lowers temps. Big difference after installing the new one. That will lean out the HC-CO reading.

Do the EGR stall test- That'll increase your NO if not working .


I would say a stock Cat might last 20 years . About what I got out of mine. 23 years is pushing it . Expect 1/3 that with an aftermarket Cat

Figured it might be time for a new O2 Sensor so that gets changed too.

So , not passing is costing some extra dough, plus the inconvenience of smog every year.



$155 -Vac advance-Toy

$47- Denso O2 Sensor-

$169- Magnaflow CAT # 39886

+ Cap , rotor, plugs , wires , $ 59 for the test and don't forget our 10% sales Tax . Gotta love California. Got the cleanest air standards in the nation, but some of the dirtiest air. I wonder where it comes from? I figure as clean as our cars run, we have to be sucking air from all the other states and Mexico and cleaning their air too.

People do not realize how much pollution commercial airliners put out. I've heard 10,000 pounds of fuel during a take off.
That sounds a little high to me but half that is still an awe full lot. The day after 911 and the planes were all grounded the skies over Sacramento were pristine.

This something no one wants to talk about.

I just went through the pollution gauntlet here in Colorado....Turns out my cat was bad. Unfortunately, My engine is a '97 and has the OBDII system...so this whole story probably isn't going to be all that helpful for you....but...

First time I went in, I failed. Which wasn't entirely surprising to me because my ECU had been throwing O2 sensor codes at me. While driving up at really high elevation (around 11,000 feet), I would get a code that basically said my O2 sensor readings were "ambiguous". Not sure exactly how to interpret that, I would just clear the codes and go on with life. The check engine light only came on at those high elevation...so I really didn't think too much of it.

Also, after failing emissions that first time, I found out that the EPA has LOWERED the acceptable emissions level...for all cars. And not by a small amount either; the acceptable levels for HC and NOx, for a '97 SUV, have been lowered to 1/3 of the levels that were acceptable in 2008. So...that was a BIG surprise.

After playing around on here and talking to my local Yota parts department guy, I cleaned my MAF and replaced my primary O2 sensor (the one before the cat). This did have a noticeable effect, during the second emissions test. My readings dropped by around 15%....but, I was still getting twice the acceptable levels for HC and NOx. Which was really disconcerting, because these were the lowest levels that I've ever gotten from this motor (I kept the results from the previous tests).

Now desperate, and thinking I would never get this motor to pass emissions, I bought an OBD2Link and software package for my laptop. This is now a must have tool for '96 and newer vehicles...this thing is great. I can connect my laptop up to my ECU and get actual real time readings from the engine sensors. Not just read codes, but actually see what the sensors readings are and how they are responding, what the timing advance is doing...how the fuel trims are responding.....all while the engine is running....it's really cool.

Anyway...the very first thing I noticed, after connecting the OBDLink up (and even before fully understanding the power of the software package) was that my O2 sensor readings were flat. My truck has an O2 sensor before the cat (the primary) and a second sensor after the cat (the secondary). If the catalytic converter is working at all, there should be a change in the reading from the primary to the secondary....I had nothing, both read 0.8 volts at idle, and did changed but stayed equal to each other when I gave it gas. So, I was pretty certain my cat wasn't working at this point.

So...a little online research later and I found out that flowmaster cat's are basically junk. Which sucks 'cause I had put a flowmaster cat in there when I did the 3.4l motor swap a few years back. I couldn't find one positive customer review of the things online.

My next move was to install a Walker catalytic converter (which got good reviews and costs about the same as a flowmaster). I hooked up the OBDLink and now I'm getting a 0.2 volt difference between the two O2 sensors at idle (primary was 0.8v, secondary was 0.6 volts. Then it was off to the smog police....for a 3rd try.

The difference was HUGE. My HC, CO and NOx exhaust gas readings are now a fraction of what is allowable. Needless to say, I'm now legal (and re-registered in Colorado).

A few things I learned from my research/experience....
- with catalytic converters, bigger is definitely better. The bigger the cat, the more free flowing it is, AND the more effective it is, and the longer it will last. The cat I put into my '93 4Runner with a 1997 3.4L v6, was sized for a 5.7L motor.
- I also learned that catalytic converters are specifically made for 1996 and later vehicles with the OBDII system. I'm not sure what the differences actually are, but most aftermarket manufacturers sell standard cats and OBDII cats.
-The final lesson was that the flowmaster cat I had originally installed was probably never doing anything to effect the exhaust gases. Before replacing the cat, I was getting almost exactly the same readings as I had got right after doing the motor swap (which doesn't pass the current standards).


Sorry for the long post...but, I hope that helps.

For CA folks, I just found this website that is quite interesting:

http://data.fresnobeehive.com/air/smogck.php

Basically you plug in your plate # or VIN and it shows you where your vehicle landed amongst readings from all other vehicles of that type.

Interesting stuff.

CORunner93 ,

Good post , not too long. I suggest if anyone intends to drive in the future they pay attention to this stuff because they're eventually going to be faced with the same situation-- especially if we're going to continue to enjoy our relic vehicles. The emission standards are tightening on a regualr basis. It's going to get tougher.

If you have time could you start a new thread on the OBDII
hardware and software (all the pieces) you have and where you get/got it . I am only aware of readers you can buy at tool stores/autoparts etc. and don't really know much about it. I would be interested in that info. Thanks

Thanks Cholltero....I always fear that I'm being a bit long winded with some of these posts. I would be happy to do a write on up OBD stuff, but unfortunately I really don't know all that much....the post I did earlier is really my first experience with that stuff. There is a Tech Article here on 4x4Wire, already. The article is a bit dated (some new technologies have been introduced since that article was written), but it was an informative article....that's where I started 2 weeks ago.

I can tell you this (the basics)....you need 2 items to be able to read sensor data...(1) an OBDII link device, which will rectify the voltages and signals so that your computer can read them (without burning the computer up), and (2) a software package that can read the input and display the date. The most common package I found was a device called "OBDLink" made by a company called Scantools and the software was called "ScanXL" by a software company named Palmer. I bought the whole package (link device and software) on Amazon.com for about $180 with shipping. Both companies have pretty informative websites and customer service contacts that are pretty helpful....and as best I can tell, the stuff does exactly what they say it does. There were other similar link devices out there...and other software packages but the setup I got seemed to be the most popular. And both companies offer multiple versions of their stuff (I went with the 'standard" package.

Anyway....all the info is available on the web....just do a search for "OBDII Link"....you'll get a ton of stuff.