Hopefully someone has some experience they can share with me on this one.

I have a 2001 Civic EX. VTEC motor. This car has been 100% reliable until now, and has had *all* the factory recommended maintenance done to it (by me). 117k miles. New timing belt at 105k. This is why it didn't take me very long to replace the sensor - I knew right where the little bugger lives. But this latest problem has me stumped.

A few nights ago, the CEL came on. Car ran fine, Leilani took it to work the next day. On the way to work, fine. When she tried to drive it home, it didn't want to start, finally did, idled like crap, ran rough, and stalled repeatedly. She brought it home and I bought an OBD-II code reader the next day (finally, an excuse to get one!). The code was for the camshaft position sensor out of range/not responding. $45 part from the dealer, it took me about 3 hours to replace it. Test drive it, runs fine, no codes.

Leilani takes it for some errands. Calls me later, tells me it's acting up again. Runs rough, stalls, etc.

Hook it back up to the reader, P0420 - Catalyst System Efficiency Below Threshold.

Great - what does that mean? A new cat, or a bad O2 sensor? I clear the codes and take it for a ride, as I still haven't had it act up on me. The car starts OK, but immediately runs like crap. I take it to the end of the street and limp back. Put it on the reader again, P0301 - Cylinder 1 Misfire. No P0420 code this time.

I took out the spark plug and the coil module, and both look fine. I made sure the connections were tight and there was no corrosion. Put it back together, it runs fine. I clear the codes and take it for a 30 minute drive. No problems whatsoever.

Put the reader on it for kicks, and P0301 comes up again. I *thought* it missed once, but I was running it pretty hard and I thought it might have been the VTEC kicking in, which feels somewhat like a miss.

I'm letting it cool down and I'm going to drive it again later after clearing the codes. If I get the misfire code, I'm going to swap coil modules between cylinders and see if the code follows the module around.

Right now, I'm thinking that I have an intermittent coil module, which was causing raw fuel to get dumped into the exhaust, which was throwing off the efficiency of the cat. I didn't get the misfire code and the cat code at the same time, but it seems reasonable anyway.

However, this doesn't explain the camshaft sensor code, and I think it's odd that sensor would fail anyway as it's just a magnet wrapped in copper wire and encased in plastic. No moving parts, nothing to fail. The connector looked fine, no corrosion, no exposed wires or anything else.

Am I missing anything? Does anybody have an idea what might be happening with this car?

Thanks!!!!

The CMP sensor could have been going out for a while and just needed to be replaced. I know on my brother's PSD it's somewhat of a 'regular maintenance' part. But generally when they go out, the engine just stops working all together.

As for the catalyst code--- if the problem was in the cat, I would highly doubt that it would cause then engine to perform poorly, unless of course it was clogged. Between cat and o2 sensor, for that code, I'd put my money on the o2 sensor.

I would start with the 02 sensor, since it's due for one anyway. Also it is due for a new Cat as well... those generally should be changed after 60k, according to my muffler guy and yes, I trust his word.
if it IS the cat, your cylinder 1 misfire could be due to backpressure.

mrfixit said:

I would start with the 02 sensor, since it's due for one anyway. Also it is due for a new Cat as well... those generally should be changed after 60k, according to my muffler guy and yes, I trust his word.
if it IS the cat, your cylinder 1 misfire could be due to backpressure.

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If both of those parts are stock then you've already eeked a LOT more life out of them than you rightfully should have

That's what I'm afraid of. I don't know what it costs to replace a cat in this thing, but it won't be cheap.

However, a bad cat doesn't explain the misfire in cylinder 1. But a misfire would cause raw fuel to get dumped into the exhaust, which might explain the cat code. So I'm inclined to check/replace the coil packs first.

Anybody know if there's a test procedure for these things?

I know for a fact that VERY few people ever have to replace the cats on their cars. Most go for a LONG time before they need it.

Also, if it were a cat or O2 sensor, it wouldn't affect drivability *that* much, would it? I can see reduced gas mileage, but rough idle? Stalling?

Just google "catalytic converter replacement intervals" and argue with those links. consensus is 30k to 50k. doesn't mean they all FAIL there, but your performance can suffer beyond that point. A good way to check to see if it IS plugged is to pull the O2 sensor before the cat and see if it acts any better, performance-wise.
Contrary to what you might think, the backpressure from even a partially clogged converter can give the sensors a false reading, as in TOO RICH, and they lean out the fuel. Too much lean, a misfire. too much exhaust pressure, and the cylinders don't exhaust well...
To test your coil to see if it's firing, an inductive timing light would do the trick.

Tom's correct. And yes a plugged cat CAN affect performance *that* much. You're basically strangling your engine if your exhaust is plugged up. Stalling is not an uncommon symptom for a plugged cat.

I highly doubt that the cat or the o2 sensors are causing that misfire.
you can test the voltages on the o2's to see if they are inrange. Why waste money on replacing good parts.
the cat code was because if the misfire plain and simple. doubt it plugged the cat that fast.
The plug I would replace and swap the coil packs around. could be a bad injector also put a NOID light on it and check the injector.

You're right that a misfire possibly can kill a cat, depending on what caused the misfire. The o2 sensor is likely doing its job, but, keep in mind the connectors for the o2 sensors are living in a pretty hostile environment. Water intrusion into a connector has given more than just one tech bad headaches. Fuel pressure tests are in order, along with noid lights.

Skandocious said:

Tom's correct. And yes a plugged cat CAN affect performance *that* much. You're basically strangling your engine if your exhaust is plugged up. Stalling is not an uncommon symptom for a plugged cat.

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Ok, but then why did it run fine for 30 minutes today? An intermittent plugged cat?

smokey said:

I highly doubt that the cat or the o2 sensors are causing that misfire.

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I agree - it seems unlikely.

you can test the voltages on the o2's to see if they are inrange. Why waste money on replacing good parts.

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Can you explain exactly how to do that? Do I measure voltage across the O2 sensor pins while the car is running? Cold or hot?

The plug I would replace and swap the coil packs around. could be a bad injector also put a NOID light on it and check the injector.

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The plug in the #1 cylinder looked fine. It's got about 15k miles on it, and was gapped correctly. I don't have a noid light set. How much would one of these set me back? Always looking for an excuse to buy more tools.

mrfixit said:

Just google "catalytic converter replacement intervals" and argue with those links.

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Ok wise guy... I did. No results with quotes. I removed the quotes and didn't find a single reference to replacing the cats within 30k to 50k. I did see one manufacturer maintenance schedule that went to 100k with no mention of replacing the cats. So I'm gonna have to throw the BS flag on this one.

I will check the owner's manual later tonight, but I'm betting it won't be mentioned in there, either.

doesn't mean they all FAIL there, but your performance can suffer beyond that point.

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Performance starts to suffer on nearly every component in a vehicle as soon as you drive it off the showroom floor.

Contrary to what you might think, the backpressure from even a partially clogged converter can give the sensors a false reading, as in TOO RICH, and they lean out the fuel. Too much lean, a misfire. too much exhaust pressure, and the cylinders don't exhaust well...

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So what's the explanation for the intermittent behavior? How could the cat be clogged bad enough to cause the engine to stall one day, but the car drives perfectly fine the next day?

To test your coil to see if it's firing, an inductive timing light would do the trick.

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An inductive timing light on a car with coil-on-plug modules?

First of all, I looked it up BEFORE I said so. It was there; ya gotta read sometimes past the google page, but it is there.
Why would I make this stuff up?
Why did I even bother answering?

On edit, I STILL had the danged screen up in a tab! Here it is:



Lemme know if you need a bigger version.

As for the inductive light, you would have to run a jump cable. I forget not everyone has one.

to test O2 senosors here is a page with info
http://mr2.com/TEXT/O2_Sensor.html
NOID lights run from 10 to 40 bucks bepending on how big a set you get.

So I thought it was fixed yesterday. I drove it all the way to pick Leilani up from work, and right when I pulled in the driveway (15 min drive) it started acting up. Still getting the P0301 code, cylinder #1 misfire. Drove it home and parked it. Started it up this morning, no problems.

Now I see a pattern. It always runs fine in the morning. Afternoon, not so good. Morning temps here are around 60. Daytime highs normally touch 100 or close to it. So it looks heat-related as the car always sits out in the sun all day. I replaced the #1 ignition coil because it seemed reasonable the coil was failing when it gets really hot.

Drove it around right after, no problem. Ok, if past behavior is any indication, it should act up if I take it for a ride around 3 in the afternoon.

Well, I started it up a few minutes ago - immediately ran rough at idle all the way through the RPM range. Pulled the codes - cylinder #1 misfire. ARGH. It ran just a minute or so before I shut it down. I swapped the #1 and #4 ignition coils, fired it up, runs fine now.

I just took it for a 10 minute ride around town - no problems. Ran great the whole way, didn't set any codes.

I haven't seen the converter code again, either.

What is going on with this car? It seems to do what it wants when it wants to.

Next steps: check for vacuum leaks. Get noid lights and see what's happening with the injectors.

I would replace that plug not a expensive item. Could have a minute crack in the porcelain that is letting it short out when it gets warm. I have seen it in the past and it drove me near looney figuring it out.

If you have a little moisture in #1 hole, you'll get a misfire on that cyl. Theres a little gasket that keeps oil from seeping into the hole. Check to see if theres any oil in there.

All of this sounds suspisciously like an intermittent connection somewhere. If the EEC drops into 'limp' mode it makes all kinds of stuff go out the window.