ffspiel

The skinny...

I own a 99 Civic EX with Vtec engine. It's been stalling, when it's warm, and threw an engine code of P0420. I've removed the Catalytic converter but not sure what a bad one is supposed to look like. I've read that I shoud be able to see light through the other end, and if not it's probably bad... is this a good way to diagnose the prob while it's out.

Other Cat findings... shaking it with the o2 sensor off chunks of debris are falling out of the hole... look like greyish charcoal. Finally, the O2 sensor that was attached to the CAT has got a screen on it that looks melted to the sensor tip... is this normal after 160k miles? Thanks.. rob

94EG8

That would be a bad cat.

Replace the catalytic convterter, probable cause for it going bad? Bad O2 sensor, causing it to run in open loop mode causing it to run excessively rich destroying the cat, i'd probably replace both O2 sensors at the same time, the rear only because it sounds like its melted.

esean93

dude my cat has 186k and im still running it!does your car back fire alot or something?

ffspiel

No... no backfire, nothing; problem just showed up as intermittant stalling, getting worse.

I pulled the CAT and the honeycomb is broken... parts floating about on the inside.

I also did a test on the O2 sensor... it works, but not up to specs. Im purchasing another.

Thanks for the help guys; I'll keep you informed... regards... rob

PhuCDatBiCh

my car does the same thing when it cold outside check engine go away when it hot check engine show up and my car back fire sometime

honda.lioness

Looks like you are on the path to full correction, but just a few comments more:

--From my reading just because one can see light through the cat does not prove it is still good. If it is completely dark (and so blocked), then (okay, doh) it is plugged and no good. Then the question is why did it plug? Word on the street still is that cats are supposed to last forever. Only bad fuel or improper fuel-air ratios should foul them.

--As others noted, chunks falling off is a dead giveaway that the cat has failed.

--Are you talking about the upstream O2 sensor? What you describe is not normal. Again the question becomes what caused this.

--O2 sensors can die in as little as 50k miles. Their response can be degraded enough after 150k miles to still cause the car to sound and drive fine, but then a person drives it to the emissions station, and the car flunks. Worse, a degraded O2 sensor is going to tend to destroy the cat, too. I would say that, if one is going to change the cat, and no codes are being thrown, change the sensor, too. Which it sounds like you are doing. :-)

ffspiel

Agreed, fixing the CAT is only half the problem... other causes affect the early death of a CAT and best case scenario they should last forever given proper engine conditions.

In my situation I don't know what's caused my problems. The engine has an oil leak and has had the recall ignition swith situation. In removing the CAT, I found that the downstream O2 sensor was not operating within it's normal parameters (I tested it following instructions I found on the web. It worked, but not right), perhaps causing the early burnout.

I also stumbled upon a Honda repair bulletin (google Honda Service Bulletin # 05-027) that highlighted a potential cause of premature failure of these things as the prongs on the ignition box in the distibuter not connecting properly (..causing fuel/air mix problems?), if I understood it correctly.

I ordered an OEM Cat and downstream O2 sensor... I'll update when things are done. Thanks for everything... rob

ffspiel

... the O2 sensor I'm describing is the one screwed into the CAT... it's the downstream one, right?

honda.lioness

#41 = upstream
#28 = downstream

94EG8

Yes, it is. But it doesn't actually affect the air fuel mixture, its basically just there to monitor whether or not the cat is doing its job. The upstream one is what affects the air/fuel mixture (and what may have lead to the demise of your cat)

lenseyer

I also got this error code P0420 Below threshold Bank 1 and went to an auto shop to have this fixed. The mechanic replaced my oxygen sensor (the one attached after the cat converter). He erased the error code but after driving the car the next day, the engine check light again. Are there two sensors for this model?

honda.lioness

See what the code is now. If it is still P0420, I would be investigating whether your cat converter is destroyed. There is always at least one sensor upstream of the catalytic converter whose signal dominates by far in determing the fuel-air ratio command from the ECU. (The downstream sensor on some or all automobiles from my reading may have a small but detectable direct effect on fuel trim.)

ffspiel

Yes.. .the CAT is hammered. I looked through it; no light on the other side. I looked into it and 1/5th of the honeycomb is broken on the upstream side... honeycomb on the interior is nearly completely hammered and in little chunks.

I'll replace the upstream O2 sensor in the next couple months.... I just spent 900 for the OEM CAT and downstream sensor (I opted for this option because it's CA emmisions and I'm not modifying THIS ride....).

Parts should be both in by Monday... I'll install and see if the stalling problem has been resolved. Pray for me. (Thanks Lioness.... ) ~ rob

ffspiel

Yes... two sensors on the 99 Honda Civic EX (items 41.. upstream of the CAT, and 28.. on the CAT). If you get a chance, check out the diagram Lioness has so graciously embedded in the thread for us..... rob

honda.lioness

Hey Rob, I would be a tad concerned that, without the new upstream sensor, the brand new OEM (=big bucks) cat will get destroyed. I think I would at least ask around about how long it takes to destroy a cat with an iffy upstream O2 sensor, especially given the severity of the damage your cat now has. Of course, you could have just got a tank of bad gas. As I understand it, the impurities attach to the cat and then cause its parts to melt, leaving the effect you are seeing.

I hope you are buying your O2 sensor online and it is either Denso or NGK. Online is a lot cheaper. NGK is the likely OEM maker for your sensor, though it could be Denso, too.

You might get $25 to $100 for the old cat, btw. I sold my 91 civic's original, OEM cat for $25 in September to a junkyard. The cats have precious metals in them that make them a good deal for junkyards (and thieves lately, too). Call around the wrecking yards where you are and go for the highest price.

Good luck.

ffspiel

The sensor's OEM too; I'll look into the NGK for the upstream one, money's tight right now as a result of the repair. Thanks for the manufacterer tip, by the way.

Yeah... online is cheaper, but not by much when it comes to Honda OEM. I found the best price for what I was looking for at HondaPartsNow, but their shipping's pretty pricey. They were about 150.00 cheaper for the CAT then the local dealer though, so not too bad if I'm getting hosed anyhow

Hope you have a good weekend, Lioness... ~rob

ffspiel

Lioness... just another question.

I'm familiar with NGK, however, looking them up on the internet they don't seem to be real easy to find (O2 sensor-wise). Is it possible you ment NTK? If in fact you ment NGK, then do you have a source you can suggest or have delt with in the past? Thx... rob

dividedas1

pisssh emissions. glad they don't exist in iLL for obd1 cars. and you could get a new cat from autozone or what ever for like 70$ (get a direct fit one) and hanging the pipe is easy as long as you got some car jacks and jack stands. and some hand tools. some of the bolts might be rusted real bad on there though.

ffspiel

Yeah... you're right.. lucky to be in Illinois (except for the politics, right?). No so much luck with Cali... can't get catalytic converters through Autozone or Chief (probably noone else of that type, for that matter.. .that is, legally).. .so, we spend the big bucks here in the Golden State... (no wonder it's golden... they've got all my duckettes on this repair, jeeze...!). later.

honda.lioness

You're right; NTK is more accurate, since it is the O2 sensor branch of NGK. Double check me on this because I do not know if you have any swaps in place or not, but from ngksparkplugs.com , I think you want NTK oxygen sensor #24631 for the pre-cat one. Try http://store.summitracing.com/egnsea...15+1005+401124 . $113 plus whatever they want for s/h. ISTR that summitracing has been mentioned around here as having some of the best prices for oxygen sensors. I have not dealt with them but would be willing to, since so many here have.

The NTK price looks like it is going to beat easily the Denso equivalent price in this instance.

As you may be aware, the good news on the OEM cat is that they are supposed to last longer than the aftermarket ones, like truly a lifetime (barring abuse) vs. a few years.

Except for the politics indeed ha ha. :-)

ffspiel

Hey Lioness... is your name "Elle".... (cute name).

In my haste, I believe I ordered the wrong O2 sensor, probably have to send it back. I ordered a 24625, but the application calls for, as you stated, the 24631, but I ordered before I read this post. ... duh.

honda.lioness

Here's my understanding FWIW: The difference is that the 24625 sensor has a male connector and the 24631 has a female connector. Note how the good O2 sensor stores show photos of the connectors to help customers. In theory you could wire (not plug and play) the 24625 one up and it will work fine. But wire splicing is a little annoying (though quite doable) plus you get to worry that the signal will get fouled up or the sensor will be destroyed if you do not get the correct wires spliced. Heckuva lot of queries here about what wire color on the new sensor goes with what on the stock connector. If you're good at wiring diagrams, no big deal. They're both 4-wire sensors. All O2 sensors (1-wire, 3-wire, 4-wire yada) have one wire that sends the exact same voltage signal to the ECU (oscillating rapidly around 0.45 V, where 0.45 V denotes a perfect air-fuel ratio). All 4-wire sensors have a heater all powered at the same voltage as well, accounting for two of the wires.

Better news: Send the sensor back for a refund or exchange, and the cheapest U.S. mail shipment should cost only around $2.00.

The difference in price on these two sensors is not going by me, BTW. Same sensor, different connector, from my reading. I cannot explain this. My best guess is it is a manufacturing idiosyncrasy.

One of the older wiser DIYers here may chime in and correct some of the above. Stay tuned.

P.S. Like others, I do not envy you passing California emissions. More threads here on failing emissions wind up unconcluded. Still, a new cat should fix things up at least for the short run. Come two years or whenever emissions testing are next required, we'll see how that OEM cat (with new sensors) has held up. I think it will turn out to be a good investment, on the premise you want to keep the car around another ten years and/or want a good price on re-sale, meaning it is passing emissions.

ffspiel

Thx Lioness.....

lenseyer

lenseyer

Thanks a lot...I'll check on the code and we can go from there....Happy weekend guys