Just curious, on my old CR-V, I've got the old P0240 CEL for cat/front o2 sensor/whatever. I replaced the cat about 3-4 years ago but did so w/ a cheap aftermarket model. I've gone ahead and ordered new front and rear o2 sensors and Magnaflo replacement cat (a step up from what I bought before). But just wondering what else I can do to cover my bases here. I noticed w/ my Scangauge that the mpg has dropped to around 17 mpg and acceleration is very sluggish. Even when I reset the CEL, the mpg is staying low and accel is still slow. Could this be a clogged cat or just the result of a super rich a/f ratio due to the failing cat? Anything else I should replace?
Cat/O2 Sensor/MPG/Acceleration question
- Thread starter BrianWC
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Bad front o2 will kill the cat. Make sure no metered air leaks, misfire count low, secure engine and BAT GNDS
Oh I also replaced the front o2. However, I went through 2 cheapo Bosch universal ones trying to save money before getting a Denso OE sensor. Perhaps I ruined the replacement cat before getting the "good" o2 sensor on there...idk...
Like I said, I've got all new stuff coming for it. I haven't looked for leaks but don't THINK I have any. I keep this car in pretty good repair. I've just ignored CEL for a while b/c it's mainly our sitter/nanny/whatever that drives it and she always forgets to tighten the gas cap, tripping that code. So I was suprised when I went to clear it out last time and discovered I have 2 codes... But I can def tell a difference in acceleration and mpg. And since we moved into a secluded neighborhood on the far edge of the burbs, the mpg bothers me more than it used to...
Like I said, I've got all new stuff coming for it. I haven't looked for leaks but don't THINK I have any. I keep this car in pretty good repair. I've just ignored CEL for a while b/c it's mainly our sitter/nanny/whatever that drives it and she always forgets to tighten the gas cap, tripping that code. So I was suprised when I went to clear it out last time and discovered I have 2 codes... But I can def tell a difference in acceleration and mpg. And since we moved into a secluded neighborhood on the far edge of the burbs, the mpg bothers me more than it used to...
A plugged catalytic converter can cause all of these issues. Since you have a proper OE sensor now and a new cat on the way, these issues will most likely go away.
Aftermarket cats, especially cheaper ones, are not known for their longevity.
Aftermarket cats, especially cheaper ones, are not known for their longevity.
On some vehicles when the O2 sensor fails, it fails in the "rich" condition, so that's a possibility.
A restricted cat might cause the issue; if there's a performance reduction at higher rpm you could suspect that; but if the engine is fine through the rpm range the cat should be ok....but the acceleration issue is still there.....
A restricted cat might cause the issue; if there's a performance reduction at higher rpm you could suspect that; but if the engine is fine through the rpm range the cat should be ok....but the acceleration issue is still there.....
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You bought a magnaflow which is like buying a 50% efficiency oil filter. Great flow, but the media doesn't filter (burn off) much exhaust gas. Nothing wrong with the cat you bought, simply does not match the catalyst efficiency threshold of the car's ecu.
The rear o2 sensor does nothing but gather post cat exhaust stats that determine whether to trip the P0420 catalyst efficiency code. By replacing the rear o2 you will make it more sensitive, more likely to trip a P0420, so leave the rear o2 sensor fouled. I covered mine up with a $6 spark plug non-fouler. Plenty of diy's out there to follow. I also have a few threads on here regarding it.
The front o2 is dual role, gathering pre-cat exhausts stats and also adjusting the air fuel trim which could effect the gas mileage if it was to get lazy. Denso o2 sensors have dropped substantially, use them. Go to the denso site and get the exact o2 number. Then you should be able to find on amazon, rockauto, etc. Don't use the universal Bosch, etc. Too important a part.
Resetting/clearing the CEL will only make it go away until (X) number of driving cycle stats have been gathered, comes back on in a day or so.
Could a lazy front/pre-cat o2 sensor flood the cat with unburnt fuel overloading the media tripping a P0420? possible. A 1/10 possibility.
So...Replace the front o2, use the non-fouler over the rear o2. Leave the magnaflo, should still be ok. That should do it.
Also..are you burning a ton of oil? Usually the core issue.
The rear o2 sensor does nothing but gather post cat exhaust stats that determine whether to trip the P0420 catalyst efficiency code. By replacing the rear o2 you will make it more sensitive, more likely to trip a P0420, so leave the rear o2 sensor fouled. I covered mine up with a $6 spark plug non-fouler. Plenty of diy's out there to follow. I also have a few threads on here regarding it.
The front o2 is dual role, gathering pre-cat exhausts stats and also adjusting the air fuel trim which could effect the gas mileage if it was to get lazy. Denso o2 sensors have dropped substantially, use them. Go to the denso site and get the exact o2 number. Then you should be able to find on amazon, rockauto, etc. Don't use the universal Bosch, etc. Too important a part.
Resetting/clearing the CEL will only make it go away until (X) number of driving cycle stats have been gathered, comes back on in a day or so.
Could a lazy front/pre-cat o2 sensor flood the cat with unburnt fuel overloading the media tripping a P0420? possible. A 1/10 possibility.
So...Replace the front o2, use the non-fouler over the rear o2. Leave the magnaflo, should still be ok. That should do it.
Also..are you burning a ton of oil? Usually the core issue.
Thanks Leaky seals. I know how to do the job and about o2 sensors and their roles. I mainly want to make sure I'm not overlooking something re the running rich.
Further, I think you misunderstood some of my details (or I wasn't clear). I replaced the cat a few years back w/ a cheapo. THAT's the one that's evidently clogged and causing trouble. I also put on universal Bosch sensors. WHen the code didn't go away, I cried uncle and got OEM direct replacement o2 sensors. Those and the replacement cat worked well for about 3 years. I realize replacement cats are not great but wasn't going to pay $11-1400 for the OE.
I have got a magnaflo on order b/c it seemed to be the best-built alternative at Rock Auto. Definitely not for performance gain. I've also got new direct replacement Denso sensors on order. When I first slapped on the cheapo cat, it was still tripping the CEL because I was using the bosch sensors. I suspect that might be when I started the new cat on its way to clogging. I just want to make sure there's nothing else I'm overlooking before I run rich again and potentially foul another cat. I didn't want to run an anti foul plug/adapter b/c I've read of people still having fuel economy issues with them so I didn't want to cloud the issue.
I don't know on what caused the OE cat or sensors to fail. I used to think my CR-V consumed oil. I've since replaced the drain plug and that miraculously accounted for all my consumption. So...no clue.
Further, I think you misunderstood some of my details (or I wasn't clear). I replaced the cat a few years back w/ a cheapo. THAT's the one that's evidently clogged and causing trouble. I also put on universal Bosch sensors. WHen the code didn't go away, I cried uncle and got OEM direct replacement o2 sensors. Those and the replacement cat worked well for about 3 years. I realize replacement cats are not great but wasn't going to pay $11-1400 for the OE.
I have got a magnaflo on order b/c it seemed to be the best-built alternative at Rock Auto. Definitely not for performance gain. I've also got new direct replacement Denso sensors on order. When I first slapped on the cheapo cat, it was still tripping the CEL because I was using the bosch sensors. I suspect that might be when I started the new cat on its way to clogging. I just want to make sure there's nothing else I'm overlooking before I run rich again and potentially foul another cat. I didn't want to run an anti foul plug/adapter b/c I've read of people still having fuel economy issues with them so I didn't want to cloud the issue.
I don't know on what caused the OE cat or sensors to fail. I used to think my CR-V consumed oil. I've since replaced the drain plug and that miraculously accounted for all my consumption. So...no clue.
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How about seeing how she drives after your new O2 sensors are in.
We can go from there.
We can go from there.
Originally Posted By: BrianWC
I just want to make sure there's nothing else I'm overlooking before I run rich again and potentially foul another cat. I didn't want to run an anti foul plug/adapter b/c I've read of people still having fuel economy issues with them so I didn't want to cloud the issue.
The spark plug nonfouler only goes on the rear O2 sensor (after the cat). As previously stated, its only purpose in life is to set the P0240 code. The nonfouler tricks the O2 sensor. The rear post-cat O2 sensor has no impact on gas mileage.
I just want to make sure there's nothing else I'm overlooking before I run rich again and potentially foul another cat. I didn't want to run an anti foul plug/adapter b/c I've read of people still having fuel economy issues with them so I didn't want to cloud the issue.
The spark plug nonfouler only goes on the rear O2 sensor (after the cat). As previously stated, its only purpose in life is to set the P0240 code. The nonfouler tricks the O2 sensor. The rear post-cat O2 sensor has no impact on gas mileage.
Right I know. Point is I'd read some CR-V folks complaining about the spark plug non-fouler removing their CEL but not improving mpg. I guess b/c the root cause was still there. So I don't really want to go that route. My dash could light up like a Christmas tree for all I care. I just want the acceleration and mpg back.
Originally Posted By: BrianWC
Oh I also replaced the front o2. However, I went through 2 cheapo Bosch universal ones trying to save money before getting a Denso OE sensor. Perhaps I ruined the replacement cat before getting the "good" o2 sensor on there...idk...
There you go. High resistance at a crimp -> low voltage ->ECU sees lean -> ECU increases fuel trim -> actual mixture is rich -> poor fuel economy and a difficult environment for the catalyst to operate in.
Those things can be used to save money, but for most DIYers it's not going to work out that way unless you've got a lot of free time or it's a temporary measure.
Oh I also replaced the front o2. However, I went through 2 cheapo Bosch universal ones trying to save money before getting a Denso OE sensor. Perhaps I ruined the replacement cat before getting the "good" o2 sensor on there...idk...
There you go. High resistance at a crimp -> low voltage ->ECU sees lean -> ECU increases fuel trim -> actual mixture is rich -> poor fuel economy and a difficult environment for the catalyst to operate in.
Those things can be used to save money, but for most DIYers it's not going to work out that way unless you've got a lot of free time or it's a temporary measure.
Originally Posted By: yonyon
Originally Posted By: BrianWC
Oh I also replaced the front o2. However, I went through 2 cheapo Bosch universal ones trying to save money before getting a Denso OE sensor. Perhaps I ruined the replacement cat before getting the "good" o2 sensor on there...idk...
There you go. High resistance at a crimp -> low voltage ->ECU sees lean -> ECU increases fuel trim -> actual mixture is rich -> poor fuel economy and a difficult environment for the catalyst to operate in.
Those things can be used to save money, but for most DIYers it's not going to work out that way unless you've got a lot of free time or it's a temporary measure.
Right...But the universal ones were only on for a couple of days.
Once the Densos were put on, the CEL was off for 3.5 years. But the sluggishness is new. I'm just trying to make sure I know the whole chicken/egg sequence before I ruin more parts.
Originally Posted By: BrianWC
Oh I also replaced the front o2. However, I went through 2 cheapo Bosch universal ones trying to save money before getting a Denso OE sensor. Perhaps I ruined the replacement cat before getting the "good" o2 sensor on there...idk...
There you go. High resistance at a crimp -> low voltage ->ECU sees lean -> ECU increases fuel trim -> actual mixture is rich -> poor fuel economy and a difficult environment for the catalyst to operate in.
Those things can be used to save money, but for most DIYers it's not going to work out that way unless you've got a lot of free time or it's a temporary measure.
Right...But the universal ones were only on for a couple of days.
Once the Densos were put on, the CEL was off for 3.5 years. But the sluggishness is new. I'm just trying to make sure I know the whole chicken/egg sequence before I ruin more parts.
That sluggishness could be anything.
Why concentrate on O2 sensors??
Why concentrate on O2 sensors??
I'm not concentrating on the 02 sensors. I'm just pointing out that I had the correct sensors in as I seem to have given the impression that I left in old universal Bosch ones. That's the reason I came on here-to see if it could be something else I'm overlooking.
Ok. Job done. Cat was toast. Two big chunks fell out of the front of the cat and there was lots of dust. I also threw on the two new Denso o2 sensors. I cleared the P0240 code w/ my Scangauge and took it out for a test drive. Mpg was somewhat improved but not back up to where I was expecting. But at least it mostly stayed above 20 mpg and not 17 like before. I used to average 23-24. But the sluggishness is certainly gone.
Good work.
Any chance chunks went down stream and are in the resonator or muffler now?
I had a heckova time with a car that ran great, then lousy. Cat chunks would block the exhaust here and there with no rhyme or reason,. I found it by being so frustrated that I banged on the exhaust in anger. I heard rattling!
Any chance chunks went down stream and are in the resonator or muffler now?
I had a heckova time with a car that ran great, then lousy. Cat chunks would block the exhaust here and there with no rhyme or reason,. I found it by being so frustrated that I banged on the exhaust in anger. I heard rattling!
^what other symptoms happen?
Originally Posted By: mechtech2
Good work.
Any chance chunks went down stream and are in the resonator or muffler now?
I had a heckova time with a car that ran great, then lousy. Cat chunks would block the exhaust here and there with no rhyme or reason,. I found it by being so frustrated that I banged on the exhaust in anger. I heard rattling!
It looks like one small chunk broke off the back side of the cat. But I have no idea if it's lodged somewhere....
Good work.
Any chance chunks went down stream and are in the resonator or muffler now?
I had a heckova time with a car that ran great, then lousy. Cat chunks would block the exhaust here and there with no rhyme or reason,. I found it by being so frustrated that I banged on the exhaust in anger. I heard rattling!
It looks like one small chunk broke off the back side of the cat. But I have no idea if it's lodged somewhere....
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