O2 and Catalytic converter question
- Thread starter Rexsname
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O2 sensors put out voltage during operation (or regulate the passage of voltage) so that voltage swings back and forth, something like between .4 volts and .6 volts, constantly and rapidly. Because the o2 sensor was replaced a year ago is no reason to assume it is working correctly. More sophisticated OBDII scanners and scopes can read the sensor output in real time. It may be cycling correctly, but at an average voltage that is either high or low beyond the limits of the computer to accommodate, in which case even though working per se, it is still not working well enough to use and should be replaced.
I would also agree that it is cheaper and best to test the downstream O2 sensor before replacing the cat. Cats can fail but don't fail very often anymore unless subjected to harsh use, like dunking in cold streams regularly. The cat on my '91 Ford is original at 196,000 miles and still works fine. The cats on my Audi are at 213,000 miles and still work fine.
Clogged condition can be tested with a simple pressure gauge made for the job, screwed into the pre-cat O2 sensor bung. Back pressure between zero and one are fine. Back pressure well above one is an indication of a clogged cat. This is cheap and easy to determine, all without pulling the cat.
Even if the post-cat O2 sensor gives you a reading that indicates cat failure, it probably won't be due to clogging.
Aftermarket cats sometimes do and sometimes don't pass emissions tests. If you are subject to testing and want to replace your cat, you have to have it done by a licensed professional or it won't pass testing if they see that the cat has been changed, even if it passes a tailpipe test. If this requirement is different in your area, so be it, but be prepared. Many of the hot rod cats available simply don't pass testing requirements and are not intended to. This is not to say they won't modify exhaust sufficiently to give the post cat sensor a good reading, but that someone has not registered their product with the gumment, and been approved for use by the EPA or whomever approves such things.
I would also agree that it is cheaper and best to test the downstream O2 sensor before replacing the cat. Cats can fail but don't fail very often anymore unless subjected to harsh use, like dunking in cold streams regularly. The cat on my '91 Ford is original at 196,000 miles and still works fine. The cats on my Audi are at 213,000 miles and still work fine.
Clogged condition can be tested with a simple pressure gauge made for the job, screwed into the pre-cat O2 sensor bung. Back pressure between zero and one are fine. Back pressure well above one is an indication of a clogged cat. This is cheap and easy to determine, all without pulling the cat.
Even if the post-cat O2 sensor gives you a reading that indicates cat failure, it probably won't be due to clogging.
Aftermarket cats sometimes do and sometimes don't pass emissions tests. If you are subject to testing and want to replace your cat, you have to have it done by a licensed professional or it won't pass testing if they see that the cat has been changed, even if it passes a tailpipe test. If this requirement is different in your area, so be it, but be prepared. Many of the hot rod cats available simply don't pass testing requirements and are not intended to. This is not to say they won't modify exhaust sufficiently to give the post cat sensor a good reading, but that someone has not registered their product with the gumment, and been approved for use by the EPA or whomever approves such things.
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Sorry. I rarely look at a person's location. Since you don't need to IM your vehicle, a good aftermarket cat will serve nicely at far less than the cost of OEM. Most any of them should provide catalyzed exhaust sufficient for system requirements.
Seems to me that you can avoid use of the downstream O2 sensor with dummy electronics, but I have not paid a lot of attention to this. The first O2 sensor will regulate the injection system without a cat, as I do on my 5.0L Ford engine in the Jeep. The Ford EEC-IV system didn't use a secondary O2 sensor so I didn't have to do anything other than install O2 sensors in each exhaust tube. For the later OBDII systems, as long as the secondary sensor is providing a median signal, the computer won't know whether you have or don't have a cat, so you could cut it out of the system if you have a signal source. I would have to look around to see what is out there for the purpose.
But to answer your question about after market cats, they are okay, but as with most things, you get what you pay for. Cats use rare metals and high tech ceramics in their construction, and are not cheap to manufacture, so if you find one for dirt cheap, it isn't likely to be high quality or durable in construction. I would expect to pay around $150 or $160 for a good cat.
O2 sensors are just plugged in. No fussing or special tools. The nut part of the body is delicate so use a wrench that actually fits. Many are now metric (18mm I think) and I would not use a US spec wrench. You can use a crescent if the sensor is not stuck or jammed, but if a firm bump doesn't get it going with a crescent, I would find a proper sized box end wrench or one intended for tube nuts, as found on brake lines.
OBDII is an adaptive system. When you pull out one sensor and install another, the computer is going to be a bit confused at first because of signal shift. No two sensors are identical, and the OBDII tracks and records signals from sensors every time you run the motor. Point is, once you install a new O2, especially if the original one was DOA, it might take a few miles for the computer to log and adapt to the new signal, because it will have been adding or subtracting [comparatively] large voltage numbers to normalize the signal actually received from the old sensor. it will start by adding or subtracting these same adjusting or calibrating amounts to your new signal, which it won't need to do, but it takes a bit of time to realize the difference, and adjust. You should not have to do anything special, just be patient. During install, use a small amount of anti-seize on the threads, but DON'T get any on the sensor. Also, don't get anti-freeze on it, as this can kill a sensor instantly. I would not expect this to be an issue in simply replacing a sensor, but store the information for future reference if you ever have to pull a head, or if you have a broken head gasket. Ingested glycol will kill the sensors. Treat the sensor tip as if it were a halogen light bulb and don't touch it or allow anything else to touch it when installing it. Don't try to clean one, either, as it won't work.
Seems to me that you can avoid use of the downstream O2 sensor with dummy electronics, but I have not paid a lot of attention to this. The first O2 sensor will regulate the injection system without a cat, as I do on my 5.0L Ford engine in the Jeep. The Ford EEC-IV system didn't use a secondary O2 sensor so I didn't have to do anything other than install O2 sensors in each exhaust tube. For the later OBDII systems, as long as the secondary sensor is providing a median signal, the computer won't know whether you have or don't have a cat, so you could cut it out of the system if you have a signal source. I would have to look around to see what is out there for the purpose.
But to answer your question about after market cats, they are okay, but as with most things, you get what you pay for. Cats use rare metals and high tech ceramics in their construction, and are not cheap to manufacture, so if you find one for dirt cheap, it isn't likely to be high quality or durable in construction. I would expect to pay around $150 or $160 for a good cat.
O2 sensors are just plugged in. No fussing or special tools. The nut part of the body is delicate so use a wrench that actually fits. Many are now metric (18mm I think) and I would not use a US spec wrench. You can use a crescent if the sensor is not stuck or jammed, but if a firm bump doesn't get it going with a crescent, I would find a proper sized box end wrench or one intended for tube nuts, as found on brake lines.
OBDII is an adaptive system. When you pull out one sensor and install another, the computer is going to be a bit confused at first because of signal shift. No two sensors are identical, and the OBDII tracks and records signals from sensors every time you run the motor. Point is, once you install a new O2, especially if the original one was DOA, it might take a few miles for the computer to log and adapt to the new signal, because it will have been adding or subtracting [comparatively] large voltage numbers to normalize the signal actually received from the old sensor. it will start by adding or subtracting these same adjusting or calibrating amounts to your new signal, which it won't need to do, but it takes a bit of time to realize the difference, and adjust. You should not have to do anything special, just be patient. During install, use a small amount of anti-seize on the threads, but DON'T get any on the sensor. Also, don't get anti-freeze on it, as this can kill a sensor instantly. I would not expect this to be an issue in simply replacing a sensor, but store the information for future reference if you ever have to pull a head, or if you have a broken head gasket. Ingested glycol will kill the sensors. Treat the sensor tip as if it were a halogen light bulb and don't touch it or allow anything else to touch it when installing it. Don't try to clean one, either, as it won't work.
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BLKNBLU
Explorer
If you get to the point that you are just looking for a "work around" here is a pretty neat solution. This is from a guy that swapped in a 3.4 to his 1990 and was getting the same code. Scroll down to post # 250. I realize you are still looking for a real fix, but thought I would throw this out there just in case.
http://www.yotatech.com/f160/elvota-s-3-4-swap-128285/index10.html
http://www.yotatech.com/f160/elvota-s-3-4-swap-128285/index10.html
ntsqd
Heretic Car Camper
I've kilt two cats in Patch. I tend to shake them apart from the higher speed exercises. The last one actually had the rear core turn sideways inside the case. That was a Negative Performance Feature! A lot of the 'smog legal' pre-runners use a "test tube" most of the time and swap in the cat before any mandated testing, then remove it afterwards. Otherwise they would go through a cat every month or so!
Technically any OBD II cat has to be replaced with a certified replacement for that specific application. Not to say that a generic cat will or won't work, just that the gumberment requires this. Non OBD II vehicles do not have this issue. Can replace their cats with pretty much any functioning cat.
Technically any OBD II cat has to be replaced with a certified replacement for that specific application. Not to say that a generic cat will or won't work, just that the gumberment requires this. Non OBD II vehicles do not have this issue. Can replace their cats with pretty much any functioning cat.
I stopped using a cat in an off roader when I converted the Jeep from 2.5L to 5.0L, and built it to race. I shook apart one cat behind the 2.5, but I think it was largely due to dunking rather than vibration, since you can only go so fast with 2 and a half squirrels running around under the hood.
For expedition use, though, I would expect most cats to live just fine.
I noticed in the Toyota Board discussion that the reason the guy had to provide a secondary sensor input was that his high flow cat would not allow the downstream sensor to work. That might answer the question posed earlier regarding whether after market cats work okay. Perhaps not always.
For expedition use, though, I would expect most cats to live just fine.
I noticed in the Toyota Board discussion that the reason the guy had to provide a secondary sensor input was that his high flow cat would not allow the downstream sensor to work. That might answer the question posed earlier regarding whether after market cats work okay. Perhaps not always.