P0420 - New cat time?

[stubborn1]

98 Prizm - 1ZZFE with 132k miles.

After getting the timing figured out on my rebuild project, I'm getting a P0420. I cleared the code and drove another 300 miles before it came back. Car is running smooth and getting 37mpg at the moment. From reading other posts here, it seems like the catalytic converter is usually the cause of the P0420. When my timing was off initially after my rebuild, I was dumping a bunch of unburnt fuel out the exhaust , so I'm guessing this is what it caused it to get worse.

Anyway, I'm trying to avoid a weld on cat and go for a direct bolt on replacement. Can anyone tell me where they got theirs for a decent price?

[crypticlineage]

Your cat may be bad, but its highly unlikely considering that you've no drivability issues.

When my cat went bad, it did so gradually over time because my engine was burning tons and tons of oil. The acceleration eventually became very sluggish and powerless.

It may be your O2 sensor tripping P0420. Check O2 sensors first (not replace of course, unless they're actually bad). Another test would be to see if there is any rattling sound coming from the cat when hit lightly with a hammer. Let the car sit down for a few hours before you do this, so everything is cooled down. If you hear rattling sound, it means the honeycomb structure containing absorbent compound has come loose and then its time to replace the cat.

Let us know how it goes. As for the pricing, my aftermarket weld on cat with 5 year / 50000 mile warranty was $275 including installation.

[stubborn1]

I guess I should have added that I was burning a quart of oil every 600 miles for the last 40k miles prior to my rebuild. I was guessing that the oil burning plus the timing being off for a little bit pushed the cat over the edge. I'll check for a rattle tomorrow.

I did find a direct bolt on convertor with the resonator and piping for $190 shipped. Installation should be quick and painless.

[toyomoho]

P0420 usually means there is a problem with the 02 (A/F) sensors, their circuits (wiring) or the CAT. The 02 (A/F) sensor signals before and after the CAT are compared by the ECU. This allows determining the efficiency of the CAT. If the signals are the same amplitude, the ECU thinks either the sensors are bad, the circuit or the CAT is operating below efficiency. It does not know specifically which part is bad.

[ShawnM]

420 is a cat effiency code. More than likely due to a worn out converter, especially since you were burning oil previously. This code is rarely set by a bad O2 sensor. The engine preformance can be normal even with a bad cat.

[stubborn1]

Cleared code and it came back this time after only 200 miles. I do have a spare O2 sensor that I could swap in the post cat position. My scan tool software shows activity with the current sensor and the voltage is within spec, but it's a quick check before I drop the cash on the convertor.

[gbell210]

I had the same code when I bought my '00 corolla. The previous owner told me he had put in a new-used engine. And told me it was the cat. I drove it for a month and it finally got down to the CEL coming on after 40 miles, but gas mileage and peformance were not changing (highway commute and getting 40mpg). I debated on changing out the O2's also, but eventually went with the a weld in Cat for $100 plus some labor. Light hasn't come back on, and still running great. If you are going to get O2 sensors, I would go toyota as their electronics are much better than Checker/Auto zone stuff. (I'll never get another starter/alternator for a toyota from them again)
Depending on what cat you get, most are usually cheaper (for weld in) or about the same as the O2 sensors.

[grendle]

Any conclusions here? I've got a similar problem.