poor gas mileage and a P0420 code
 

'97 Camry 4 cyl, automatic.

The gas mileage is less than 17 mpg. My daughter messed up my mpg calculations by adding $20 in gas between my fill-ups. So I suspect the mileage is actually worse than the 17 mpg.

I've read up on the P0429 code. Probably a bad cat.

Would like sources for or name brands of "quality" cat. conv. since all these forums all say "be sure to buy a quality cat," but never offer just what is a "quality" cat.

Also, I read some diagnostic procedures for determining if the O2 sensors are working properly using the diagnostic port in the engine compartment, but they weren't for my year. Anyone know the procedures for a '97 4-cyl and do I need an analog voltmeter to see the fluctuations?

Thanks,
Nate

A leaking exhaust system can also cause the code.

The computer does not monitor the cat itself. It monitors the exhaust gases going into and out of the cat via the 02 sensors.

If all is working correctly the 02 sensor before the cat should generate a syne wave voltage signal that varies in amplitude from below 0.4v (lean A/F) to above 0.55v (rich A/F) in less then one second (voltage variation from rich-lean or lean-rich = response time).

If the amplitude range is smaller or never gets above or lower the above values or takes more then 1 sec (response time) to vary from lean to rich or rich to lean there is a problem with the sensor.

The computer check engine system monitors response time.

The converter changes the exhaust gas A/F ratio thus the 02 sensor signal on the exhaust side shoud be different from the one on the intake side. The exhaust O2 signal will have less amplitude (a flatter signal).

If both 02 sensors are working OK and the output sensor has the same amplitude and response time as the input sensor the cat is not working and the computer will set code P0420. The computer looks for amplitude similarity of the exhaust sensor.

A ODBII code reader should be able to output the max/min voltages of the sensors. A analog meter will be to slow to react, an oscilloscope is best. You want the max/min output of the exhaust 02 sensor to be the less then the input sensor.

Note: To check sensor operation they need to be warmed up by operating the engine at 2500 rpm for 90 seconds before taking readings.

To test the complete system including cat operate engine between 2500-3000 rpm for 3 minutes before taking readings.

You need to determine what emissions spec the car was built. Federal (48 state) or California. California emissions built cars have two converters. One on the exhaust manifold and one under the chassis. The Fed car has only the under chassis cat. If a California car and the P0420 code is genuine would guess the manifold cat was bad.

As to cats, Magnaflow, Bosal premium line (not the standard line). Find out what converter type/location you need then search the internet.

Bosal has had some complaints about a smaller pipe on their exhaust manifold converter. Magnaflow may require cutting out the old cat under the chassis and welding in the new.

In looking for parts the difference between California and New York parts may be the requirement to have aftermarket emissions parts certified by the states emissions board for use in that, this can increase prices.

I have an Actron code reader. Think I'll go see what it will tell me. I did a bench test of the upstream O2 sensor using a voltmeter and propane torch (taking care not to overheat the sensor). Once warmed up, it quickly jumped up to 0.9V and then quickly back down to 0.1V when the heat was removed. Several mechanics on youtube recommended this procedure if you don't have an o-scope.

Print out of diagnostic from OBD scanner
 

I'm not really sure how to interpret these results, but it appears that at least both O2 sensors are alive. Attached is a file containing the read outs from my Actron scanner. The read outs from the O2 sensors are at the bottom of each block. I basically went from idle to about 2500 rpm every five frames or so.

I would say that this shows that my sensors are good and my cat is bad.

Agree?

Concur, given your test results and test data the cat appears bad.

On Toyota code P0420 is almost always a bad cat.

Fixed
 

I installed a new Bosal cat yesterday in a couple of hours. Twenty-four hours later and no CEL. The Bosal fit almost perfectly. The outside diameter was a little greater than the OD of the original, so the bracket strap right under the engine wouldn't close all the way. I used four washers in between the two halves, allowing me to snug the pipe and torque down the bolts. Otherwise, it was pretty easy. No seized bolts. No skinned knuckles. :)

error code table: http://www.spobd2.com/service/diagno...wnload-38.html