semvhu

My car has complained about the catalytic converter for awhile now. I've just been driving it since it seemed to drive normally anyway. However, a couple of days ago it stumbled a couple of times on the highway, just for a split second.

This morning on the way to work, I put the car in 2nd gear and accelerated hard after it warmed up. It stumbled multiple times as it accelerated, and the check engine light blinked after that. I checked the codes again. The P0420 code is still present, plus misfire codes are present; codes for each cylinder (P0301, P0302, P0303, and P0304) plus P0300 (random / multiple cylinder misfires) are present and accounted for.

Given this information, does anyone have any recommendations? I do not have the equipment to fully test out the catalytic converter to isolate it from potential O2 sensor failures, so I am not sure that it's actually the cat that's failing. However, this site at OBD-Codes suggests that the catalytic converter can cause misfires, so it seems to add up.

Also, how hard is it to replace the cat on an '05 Civic LX? I change my own oil and have eyed it before, but it looks pretty tight. Perhaps it's not as hard as it looks.

FYI, I just passed 200k miles on the car, so maybe it's time for a few non-regular-maintenance items. Lastly, bear in mind I'm just a weekend mechanic wannabe, so sometimes what I think is a cause is really an effect.

TIA

semvhu

Minor update to my research online. It would appear other forums for other cars with similar issues are suggesting the cat code is an effect caused by engine misfires. It's time for plugs anyway, and perhaps my coil packs are old enough that they're causing issues. For the moment, I'll start with ignition and go from there.

semvhu

Another thought: fuel pump? Symptoms of stumbling under acceleration apparently can be caused by a bad fuel pump. Thoughts?

ezone

Figure out the misfire problems FIRST.
Misfires can and will ruin a cat in a hurry.

----

P0420 cat code is for the cat, not O2 sensors. They have plenty of their own codes.

Do not replace the cat until the misfire problems are completely resolved. You can ruin a brand new cat in a matter of only minutes if the engine isn't running right.

At 200k, it wouldn't surprise me if the cat died a natural death.

----

If you think fuel problem, that is easily tested with an appropriate fuel pressure gauge.
A scanner that can display live data (and knowing how to use that data) could quickly indicate if a fuel delivery issue could be present or not.

Hondas fuel pumps are damned reliable IMO.
OTOH, the filter might not be.

---

semvhu

Thanks for the response. I'll put more thought into the responses later, but I had one quick question about your response.

You mentioned fuel filter. Do these cars have a separate fuel filter? All I've found online and looking ya the car itself indicates that the only "filter" is the sock on the fuel pump. Is that correct?

ezone

In addition to the strainer on the bottom (inlet) of the fuel pump, there is a filter element inside the top of the tank unit.

There is no external, inline filter.

You would have to pull the tank unit out and split it apart to replace the filter, and Honda has instructions for replacing it in the service manual, but does not sell it separately (but I understand it is available from other parts suppliers).

It's a lot of work for just a guess. I hate guessing.

I much prefer to sit in the drivers seat with my scanner and determine if there is definitely NOT any fuel delivery issue, or if there might be (takes about one minute for me to tell, once I have the scanner fired up). If there is definitely not a fuel delivery issue, then I don't pursue and I then go a different direction.

semvhu

Thanks again! What do I scan for to check the fuel system? That feels like a stupid question because I'm barely awake right now.

ezone

It's not scanning, it's a matter of interpreting (experience needed) live engine operating data that is available to be displayed on a decent scanner.

If the front O2 sensor voltage reading indicates there is no lean condition during a road test wide-open run all the way to redline through 1st and 2nd gears, then it's not a fuel delivery issue.
If that sensor showed lean under those conditions, that would indicate to me there is a true need for further testing.

HTH

2001-Civic-Ex

I'm having the same misfire codes and o2 codes any fix yet ?

semvhu

I posted the fix in another thread I had started and intended to post here as well, but I never did. My fix was probably pretty unique. The crank position sensor wiring on my car has been half-assed "fixed" at some point. I suppose the connector was replaced for some reason. Someone used crimp butt splices when installing the new connector and poorly taped it with electrical tape. Most of that tape has now come off and the connector corrodes over time. It had corroded again (a mechanic found it a few years back once with another problem) and was apparently causing the signal to be bad enough to cause my hesitations and misfires. My car finally threw a code for the crank sensor and it hit me that it had a problem before. I cleaned up the corrosion and put some dielectric grease on the sockets and it's running like a champ now.

As for the catalytic converter, I'm guessing my cat has died over time due not quite optimal performance from the bad crank sensor signal. I'm just living with it for now, but I may replace the catalytic converter soon and make sure that I keep the connector cleaned off every oil change or so.

TLDR: my situation is a bit special with a corroded crank position sensor causing my car to hesitate and misfire. I cleaned it up and it works great now.

ezone

There's like a zillion different possible causes for misfire codes.
Each case should be evaluated and diagnosed.



P0420 is never defined as an O2 sensor code.