MEngineer

Hello all,

2000 Honda Accord EX with 206,000 miles. New spark plugs probably about 10k miles ago. Runs great. I average about 21 MPG.

After the transmission problems were fixed, I still have a nagging P0420. I do hear rattling under the car, assuming this is from the catalytic converter. Since this is a CA car and I live in CA i want to make sure before I spend the $300 for a drop in replacement.

Here is a video from a scan tool showing the O2 sensor readings after driving home: https://www.dropbox.com/s/pxsuwjstif...37.16.mov?dl=0

The secondary sensor does not bounce around as much as I would expect if the converter was indeed bad, or am I mistaken?

Thoughts?

Thanks!
Dale

holmesnmanny

A lot of times you can use a temperature gun to check the temps before the cat and after it. It should be about 100 - 150 degrees hotter at the back of the cat than in the front.

MAD_MIKE

Secondary O2 monitors catalyst functionality. If it has the same amount of voltage and same amount of change as the primary, then most likely the catalyst is no longer effectively working.
Primary O2S should normally swing from rich(.9V) to lean(.1V) and back adjusting for stoich for primary combustion. Then the secondary O2S should not show any, notable, switching of the voltage after secondary combustion. It should appear to be lazy and hang out
If both sensors are showing same voltage and reacting similar in a short time frame, then the catalyst is no longer functioning.
You must determine what is the cause of the problem.

From your video, primary and secondary were both hanging around .77V with very little change. A normally running engine should have the sensor crossing over stoich(.5V) several times, unless under heavy acceleration. If both your O2s are reading correctly, and I think they are, your engine is running rich. Find out why the car is stuck in this rich running condition.

Check air filter, fuel pressure, compression, MAP sensor readings, thermo sensor readings, IAT readings, verify valves are properly adjusted(every 30Kmiles).

At 21MPG I'm assuming you have a 3.0 V6 which is within acceptable mileage.
But if you have a 2.3 four cylinder, then your car is indeed running rich and your mileage is bad.

MEngineer

This is indeed the 2.3L four cylinder.

I will take a look at all of the above. Do you have standard values that I can compare for each of them? Also a guide to check the valve clearance? I imagine I can check most of the readings from the scan tool.

Thanks!

MEngineer

New info.

I checked the value of the mentioned sensors and they all fall within range. I haven't been able to check compression or valve clearances.

I did hook up the scan tool and go for a drive and noticed the upstream HO2S remained steady at about 0.77V while the downstream HO2S varied from 0.0V to 0.95V. This makes me think the engine is adjusting between lean and rich, and the upstream HO2S nor the catalytic converter are working correctly.

See videos:

Upstream: https://www.dropbox.com/s/vh79rbg4wg...45.11.mov?dl=0

Downstream: https://www.dropbox.com/s/yq2g6d48cc...42.18.mov?dl=0

Thoughts?

Thanks!