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Discussion Starter · #1 ·
Hey all -

I have an '02 CRV and I was just changing the plugs (I bought it recently) and I noticed the spark plugs are super white! I know these cars are designed to run lean, but should the spark plugs really be ghost white?
I'm trying to diagnose a P0420 catalytic code. I've passed an emission test with flying colors, and I've tried changing the downstream O2 sensor. Something tells me there is some global issue of running to lean that is affecting the whole system. Any thoughts?
 

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Does your code reader show "Bank One" and/or fuel schedule below threshold?
Are all four spark plugs reading the same? Is the fuel pressure adequate?
Has the fuel filter been changed recently? Is it installed in the right flow direction?
Have the fuel injectors ever been changed or cleaned?
How many MPG are you getting?
Read this article: http://www.autorepairinstructions.com/archives/oxygen-sensors/
You may want to change the upstream O2 sensor. That is the one that sets the mixture along with data from other sensors.
 

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Discussion Starter · #3 ·
Does your code reader show "Bank One" and/or fuel schedule below threshold?
Are all four spark plugs reading the same? Is the fuel pressure adequate?
Has the fuel filter been changed recently? Is it installed in the right flow direction?
Have the fuel injectors ever been changed or cleaned?
How many MPG are you getting?
Read this article: http://www.autorepairinstructions.com/archives/oxygen-sensors/
You may want to change the upstream O2 sensor. That is the one that sets the mixture along with data from other sensors.
Thanks for the reply!
All four spark plugs are the same!
I have not measured the fuel pressure and (believe it or not), there isn't a fuel filter on the '02 and later models (only the small strainer/sock on the end of the fuel pump in the tank).
No knowledge of fuel injectors being replaced (previous owner), and I've never cleaned them. The engine runs really good. Maybe a bit of valve noise. Could probably use adjustment, but this is my first K-series engine and I'm not sure how it's supposed to sound. :)
Not sure on mileage exactly, but I think it's getting 25-30 on the highway. Seems about normal.

I checked out that link too. It unfortunately doesn't go into enough detail to outline the expected behavior of each of the two (different style) sensors in different driving conditions. The upstream sensor is an air/fuel (wideband) sensor, and it behaves differently than the downstream (traditional).

I could change the upstream sensor, but from what I can tell (watching the voltage output on it), it is behaving normally (constant steady output about .650V during idle and while driving it). I hate to throw money at a problem when I don't know what it is. :)

I just wondered if other people had plugs this white. :)

Thanks!
 

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That upstream sensor should not be outputting a constant voltage. It should be switching high and low. Like, if you stab the throttle, it should switch to a higher voltage indicating a richer condition. If it isn't, that is most likely the problem. Look at your long and short term fuel trims. That will tell you a lot too. Is the computer trying to add fuel, or take it away? The downstream sensor is the one that should stay somewhat steady. But it should fluctuate a little too. Just not as much as the upstream one. If that happens, your CAT is toast.
 

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Discussion Starter · #5 ·
That upstream sensor should not be outputting a constant voltage. It should be switching high and low. Like, if you stab the throttle, it should switch to a higher voltage indicating a richer condition. If it isn't, that is most likely the problem. Look at your long and short term fuel trims. That will tell you a lot too. Is the computer trying to add fuel, or take it away? The downstream sensor is the one that should stay somewhat steady. But it should fluctuate a little too. Just not as much as the upstream one. If that happens, your CAT is toast.
Hey, thanks for the reply! I thought the upstream sensor was supposed to switch back and forth rapidly, (as with all traditional O2 sensors), but I read more about these wideband/air-fuel sensors and, apparently, they don't switch back and forth the the traditional sensors. It isn't "constant", meaning, it does change slightly (at idle without my foot on the gas pedal at all), and when I drive it, it does change when I go on and off the throttle, but under constant speed (no acceleration), it stays pretty stable (around 0.625V-0.675V). It also rises in voltage with a lean condition, rather than a rich condition. ?? It's seems a bit counter-intuitive to me, but apparently this is how they are designed. ??

I will take a look at the fuel trims and see what they say.

Yeah, as I understand, if the downstream sensor is oscillating back and forth, the cat is probably bad. I'm going to check it for temperature with an infrared temp gun tonight and see what it says. Apparently, if the temp after the cat (pipe) is not that different from the temperature before the cat, that also will indicated the cat is toast.
 

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Hey, thanks for the reply! I thought the upstream sensor was supposed to switch back and forth rapidly, (as with all traditional O2 sensors), but I read more about these wideband/air-fuel sensors and, apparently, they don't switch back and forth the the traditional sensors. It isn't "constant", meaning, it does change slightly (at idle without my foot on the gas pedal at all), and when I drive it, it does change when I go on and off the throttle, but under constant speed (no acceleration), it stays pretty stable (around 0.625V-0.675V). It also rises in voltage with a lean condition, rather than a rich condition. ?? It's seems a bit counter-intuitive to me, but apparently this is how they are designed. ??

I will take a look at the fuel trims and see what they say.

Yeah, as I understand, if the downstream sensor is oscillating back and forth, the cat is probably bad. I'm going to check it for temperature with an infrared temp gun tonight and see what it says. Apparently, if the temp after the cat (pipe) is not that different from the temperature before the cat, that also will indicated the cat is toast.
You are correct. Apparently I missed the memo about these newer ones having wide band A/F sensors. The generic OBD software converts the readings from the PCM to something that looks more like the O2 sensors. A better scanner with better software would be needed to see what that sensor is actually doing accurately. All that aside, you still have an apparent lean condition. Could still be the sensor. But could also be something like a vacuum leak or something too. Check out your fuel trims and see if the PCM is trying to add, or remove fuel.
 

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Discussion Starter · #7 ·
Thanks again for the reply! Yeah, the OBD isn't reading the lambda (ratio), but does convert it to a voltage. I'll have to check the new plugs I just installed and see if they are just as white. I could have s vacuum leak I suppose, but it really runs pretty good.

I looked at the long term fuel trims too. When first looked at them, they were between 10.0-11.0. After a 30 mile drive tonight on the freeway (CEL has not come back on either), the long term fuel trim showed 4.3. What are those numbers anyway? Are they a percentage? What would those indicate?
 

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Not 100% sure. But you want to compare the short and long term. Subtract the short term from the long term. What you want is to have it come out as close to zero as possible.
 
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