Replace catalytic converter or oxygen sensor? Not sure what to do.

[Ford Man]

The inefficiency of the catalytic converter won't affect your fuel mileage unless it's stopped up. Back in the 70's & 80's when it was still legal to remove them from your own cars I removed them from nearly every car I owned and burned leaded gas. Some people used to say removing the converter would help fuel mileage, but I never saw an increase in mileage it was just that leaded fuel was less expensive than unleaded. This was back in the days when $.60 a gallon was highway robbery. Probably 75+% of the members on this forum don't even remember those days, if they were even around they were still sh1tting their pants.

[carwhat]

Thanks all for the replies and helpful information.

So it seems then that it could be that a year of oil build-up could have damaged the converter. I am not going to replace the engine as it is not worth putting that money into my car, so if I decide to replace the converter or sensor, I guess this could just happen again. Is it possible, then, to bring the car in for some sort of engine or exhaust cleaning every so often so that the oil doesn't continue to build up?

As I see it now, my options are to either just ignore everything, replace the sensor, replace the converter, or replace both. If I were to ignore the problem, and the converter became clogged, what happens besides lower gas mileage? It is illegal, then, for my mechanic to just remove the converter, is that right?

I would rather not ignore the problem though. Would you guys suggest replacing the converter first, see if the light goes away, and if not, replacing the sensor as well? Or vice versa, replacing the sensor first? Ford Man, you mentioned the light going out if the converter is working properly, after a certain amount of starts. Does that mean if the parts were replaced, the light wouldn't shut off right away, even if that part was the cause?

The check engine light was not on during the emissions test. It came on two days later.

Sorry for all of the questions, I only learn about the parts of cars and its system, it seems, as the problems related to them arise.

[nemo]

If you replace the parts with out finding the cause of the oil usage, your are domed to repeat the process. The question being how long it will last before the problem returns. Are you require to do an annual emissions inspection? Are you able to do any of the work yourself?

[Backtobasics]

The light is on because the sensor behind the converter is not seeing enough change in the "cleanliness" of the exhaust. Basically, the sensor behind the converter is a tattle-tale. The computer sees the difference between the front sensor reading and the back sensor reading, and if it doesn't see a change, it throws the code saying the converter is bad.

I wouldn't replace the rear oxygen sensor. It sounds as if it is doing its job and reporting. There are DIY and HOW TO articles on how to clean an oxygen sensor, though I have never done so.

Options:

• replace the converter, though I expect the converter will fail again, dependant on oil burning. The 80.00 universal converter doesn't sound too bad, but you might consider setting things up so you can do it yourself down the road, when the replacement converter dies. How often it will have to be replaced at 80.00 per could affect decision.
• leave the converter, and watch performance and MPG to see if the converter is becoming clogged.
• gut or remove the converter, not totally legal, but you would ensure it is not becoming a restriction and causing further problems or hurting efficiency

[Backtobasics]

Here is what I would do:
Buy the replacement converter, and have a muffler shop weld 2 flanges onto the end of the converter. Have them also weld 2 flanges into the exhaust. Have them also weld up a straight pipe with the 2 flanges. I would keep the converter for next year when you have to have the test, and bolt it in place of the straight pipe that you run daily.

While I acknowledge that a converter does the job of cleaning the exhaust for better air, I also take into account that the car is already burning oil. The converter is not going to fix that. For me, my comfort would come in knowing I am trying to be as efficient as possible, and while the car is putting out emissions, having a converter on there that is contaminated and not able to do it's job, is not really a benefit to the equation, and more of a hindrence, as it impedes exhaust flow, especially as it get more and more clogged with oil residue. I'd buy one more converter, run a straight pipe, and put the converter on before the test so it passes.

[Ford Man]

A muffler shop CAN NOT remove the converter. Removing a catalytic converter is a federal offense and punishable by up to a $25,000. fine and up to 5 years in prison. This isn't like it was back in the 70's and 80's, even then it was illegal for a shop or garage to remove them, but you could remove them yourself from your own car. If the converter gets completely stopped up the car will have very little power. I still have my doubts that the 02 sensor is playing any part in this, but you can go on ebay and buy universal 02 sensors for replacements. You have to cut the plug off your old sensor and splice it onto the new sensor, but the last time I looked they were only about $20. instead of $75+ like a new one with the plug installed. I used some universal sensors several years ago and they functioned fine. Just be sure before you order one to check to see how many wires your sensor has, some have 1 wire, some 3, some 4, and some 5. Most cars have a 4 wire sensor which is one ground, one signal to the ECU and two heater wires. Just match the colors except the two heater wires will be the same color and have to be configured the same way they were on the old sensor when installing the plug. Even if the problem is corrected and you don't reset the computer by removing the battery cable or with a code reader it will take a while for the light to go out on it's own. Oil will ruin the catalyst in the conveter, but there would have to be lots of oil getting into the exhaust to be the full reason for the failure. If you decide to replace the converter, shop around online and on ebay and you still may find a better price than $80. There's equipment for testing the catalytic converter, but I don't know who would have it or how expensive the testing is. Since you just got the car inspected you will be OK until the inspection comes around next year, but at that point it's not going to pass with the CEL on. I just remembered a friend of mine that's been a mechanic for several years told me you could clean an 02 sensor by soaking it in Sea Foam overnight. I've never tried it so I don't know whether it works or not, but even if it didn't it won't hurt the 02 sensor. To remove the 02 sensor you will either need an 02 socket or if the plug will fit through the box end of a 22 MM wrench just run the plug and wires though the wrench where you can get onto the 02 sensor with the box end. Depending on how much working room you have you may need a stubby 22 MM wrench. Also be sure to put anti seize on the threads of the sensor when you put it back in to keep the heat from seizing it where you can't ever remove it again.

[carwhat]

Originally Posted by nemo

Are you require to do an annual emissions inspection? Are you able to do any of the work yourself?

Yes I am, and I am hesitant to do anything more than very beginner by myself.

Originally Posted by Backtobasics

leave the converter, and watch performance and MPG to see if the converter is becoming clogged.

Maybe I will do this for a bit first, and if I notice a drop in performance, will replace the converter. I'm also going to check the oil even more often, so that it doesn't run low.

Originally Posted by Ford Man

If the converter gets completely stopped up the car will have very little power.

As far as pickup and mileage? It would be noticeable, right?

Originally Posted by Ford Man

Even if the problem is corrected and you don't reset the computer by removing the battery cable or with a code reader it will take a while for the light to go out on it's own.

But using a code reader, could the mechanic tell right away if he replaces the part if it was the part causing trouble? Or would I have to drive around a while first?

Thanks again for all of the replies and help.

[nemo]

If I were short on cash ( who isn't ) and not too good with a wrench, I would also take the wait and see approach while monitoring the mileage and performance. That way the closer you get to next years inspection before you replacing the parts the more likely you will pass your next inspection.

But using a code reader, could the mechanic tell right away if he replaces the part if it was the part causing trouble? Or would I have to drive around a while first?

Sometimes a code will reappear after several days. I had a car that made about 7 trips to two different shops before it was fixed. It wasn't the same problem you are having though.

Good Luck and hope to see you back here in other posts.

[Ford Man]

Originally Posted by carwhat

As far as pickup and mileage? It would be noticeable, right?

Yes

Originally Posted by carwhat

But using a code reader, could the mechanic tell right away if he replaces the part if it was the part causing trouble? Or would I have to drive around a while first?

Even if the light is turned off by a code reader the ECU has to relearn all the engine perimeters and at that point it will turn on the check engine light if there's still a fault. This process will usually take anywhere for 50-150 miles of driving. I know this isn't what you wanted to hear, but better to be informed than left guessing. The only sure fire way to find out if the catalytic converter is the problem is either throw parts at the problem (gets very expensive) or find someone that has the testing equipment for the catalytic converter.

[nemesis]

Check engine codes do not tell you which part is bad, they tell you what's being affected. Just for the future reference.