My mom just got her car renewal notice . . . 2 months ahead of time
In my opinion, that’s plenty of time to prepare and have the car pass legitimately
@GeorgeSanJose well said. The rest of you are a den of vipers! Lol, jk… Hopefully some time this week I’ll have time to switch the rear o2 sensors. I’ll let y’all know how it goes.
Oxygen sensors usually have different connectors for each location to prevent someone from connecting the vehicles harness to the wrong oxygen sensor. I believe you will find right and left sensors are not interchangeable, they have different part numbers.
Keep us informed as to how this goes. Maybe you will luck out. As to being a den of vipers that is not true. You’re simply not getting the answers you want to hear and things such as blaming failing parts as being inferior and there being a conspiracy to generate work because of the CEL has no basis in fact.
In most cases if a converter fails it failed for an outside reason; not because it was a defective part.
Just being curious and while I may not be on your good side, I might ask if that car still has the original spark plugs in it?
@Nevada_545 I did not know that. I’ll have look into it, thanks.
@ok4450 I’ll definitely keep you updated. The den of vipers comment was in jest btw. I got some really good advice here. I wasn’t the one who started the legalities and environmental issues debate. That stuff is debatable and that’s exactly what it turned into. I think we all want a cleaner environment. How we achieve that and the governments part in it is where we differ. I think it’s only fair that all vehicles are held to a fair standard. I feel that a cat should be deemed inefficient by actually testing it. Not by a dummy light. I never blamed failing parts or claimed its a great conspiracy. Things these days aren’t generally built to last and cars are becoming much harder to evaluate and repair, but I accept that. And It’s widely known and accepted that there are seriously flawed policies that are more geared to create revenue and/or stifle progress, prosperity and freedom than they are to actually help. I’m sure I’m not the only one who see’s it that way. But like you said, we are all entitled to our opinions and I respect yours. None of you are on my bad side, I appreciate all the help.
I never changed the spark plugs. It seems to run well, doesn’t run rough or misfire… But I should pull em, see how they look and check the gap?
If you go to the trouble of pulling the plugs, you might as well change them, because you’ve already done the work
Might as well also change the wires, because old wires often break when pulling them
It might cost you less than $100 for plugs and wires
I remember in the late 60s driving into LA and only being able to see the thick haze of eye piercing smog. I am thankful for the emissions regulations that are in place today.
On a 2003 trip to China, I was up on the 17th floor of a building and could not see the street below because the smog was too thick.
Our system in the US may not be perfect for how we regulated emissions, but I believe it’s far better than any of the alternatives.
My point about the spark plugs is that many car makers recommend leaving those plugs in place for 100k miles or even longer. In theory it sounds good; in practice not so much. Aged, high miles plugs can develop subtle misfires that you will not notice, will not trigger a CEL, or leave any codes.
Just wondering if aged plugs could be on shaky enough ground to cause problems that the O2 sensors and converters can’t quite compensate for.
I would really be concerned if the car has regular copper core plugs as those seem to start downhill around 30-40k miles if everything else is right. Platinums will normally go longer than that but a 100k is a bit much.
My Lincoln Mark has the 4.6 DOHC and uses copper core plugs. I change those out about every 35-40k miles tops and it’s needed.
My personal methodogy while plugs are out is to always run a compression test just to verify mechanical condition of the engine as even one cylinder dropping compression can cause problems. It’s best to sort that out while the spark plugs are out. A 4.6 in good condition should be in the 180 PSI and up range on all cylinders.
"If the P0420 code changes to bank 2, im gonna return the mils (Hopefully i get a refund) and buy a new o2 sensor."
Seroiusly…you’re gonna “ghetto rent” a mil-eliminator? I’ll give you a pass on the eco-stuff…but that’s pretty low. Do you buy synthetic oil at WalMart and return dino for the refund, too?,
"This one is in no way the EPA’s fault, the seller’s fault, or anybody else’s. It was just a bad decision, probably caused by being blinded by the car’s hot looks."
Sounds like OP bought more car than he really can afford, and having no reserve for repairs…
@db4690 : how does a “referee” factor into car care, exactly? I presume they DON’T check inflation pressures? If they find something they really don’t like, do they back your car up 15 yards?
@meanjoe75fan There are referees for smog related matters
I knew a guy who did that, and as far as I know, that was his job title
Re: switching the o2 sensors left/right as a debugging method. I think the OP already understands this would only be effective if the left and right side of the exhaust system is symmetrical, with identical corresponding sensors located in the same place (functionally) on each side.
Yes, but something you should understand as well. Why suggest something that isn’t possible? People are looking for reasonable advice. Now he may end up with two oxygen sensor bungs with damaged threads because the sensors didn’t come out without a fight.
BTW, I have found examples where someone has installed the oxygen sensors in the wrong location and stretched the harness to reach the wrong side. It can cause great confusion with the computer and grease monkey trying to find the problem.
@Nevada_545 writes …
Why suggest something that isn't possible? People are looking for reasonable advice.
Just posting an idea from the point of view of a driveway diy’er is all. Isn’t that the purpose of a car repair forum?
My understanding from what I gather from this thread is the exhaust system on this vehicle is configured as two parallel banks, each with its own cat, and both cats having an upstream o2 sensor, and a downstream o2 sensor. 4 O2 sensors in all. That seems pretty symmetrical to me, so it seems likely the two front sensors are functionally equivalent, as would be the case with the two rear sensors. Doesn’t that make perfect sense? Or am I missing something?
If it makes any sense at all, the idea of swapping the sensors left right seems like a reasonable debugging idea. In theory anyway.
Now it might not be physically possible to do. I’ve never tried to do it myself. My pre-OBD II Corolla has a cat, but doesn’t have a downstream O2 sensor. So the cat function is not directly monitored by the ECM, comparing the waveforms of the upstream vs a downstream sensor.
On the OP’s vehicle, the sensor pairs which I presume to be functionally the same (both front ones, or both rear ones) might actually be different for some reason. I think this is your point. Maybe the exhaust temp is higher on one side than the other, so a different sensor is needed. Or more likely, if they are not the same part number, the sensor pairs are functionally the same, but the length of the wiring harness for each sensor is different, right vs. left. If that’s the case, the OP would have to make that observation by visual inspection and come up with a solution, or make the decision to abandon the idea, themselves.
BTW Nevada_545, what is your suggestion for the OP to address this the original problem?
@ok4450 I still haven’t had time to check/change the plugs, but from what I understand. A slight unnoticeable misfire could possibly set off that code. Also a compression test is always a good thing to do. I checked for exhaust leaks the other day, seems ok in that department. As soon as I get around to checking the other stuff, I’ll definitely let y’all know how it went.
@meanjoe75fan I guess you can call it ghetto renting if I bought a part that doesn’t seem to work and I return it. From what I’m reading in the comments on the website I bought them from, quite a few people got bad mils not once but multiple times. I could have gotten a bad set also. So I don’t feel wrong for returning the parts in the same condition and getting a refund. Seems I’m getting crap from every end. You give me a pass on the environmental end, but want to bust my chops about returning a part that most likely don’t work. Look, I can’t please everyone. I’m gonna do what I can to get my car to pass inspection. If anyone disagrees with my method, so be it. As far as the others breaking my balls about using mils instead of doing it right, at least they are trying to help with good advice. So far I got none from you. As far as me being blinded by the cars “hot looks” that really isn’t the case at all. I can put the car out for sale tomorrow and double my money. I most likely have enough money to repair the car, but I’m not trying to pay for someone else to figure out the problem and repair it. It’s gonna take me some time, but with help I’ll figure it out and save a lot of money. At the same time I’m learning. So it’s not all bad IMO.
@Nevada_545 Ofc I’m gonna make sure they can be switched before attempting it. Im not a mechanic, but I know enough not to try swapping them before knowing they are compatible and it can be done without causing damage.
Yes OP, checking for misfires is a good idea. There’s an array of stuff you can do if you suspect the cat might be bad, but not sure.
Check for misfires, check the o2 sensor signals, engine and head coolant temp and sensors, checking o2 sensor wiring for damage, checking the fuel pressure, exhaust leaks (you’ve already checked apparently), exhaust restrictions, intake manifold pressures (compare, with various portions of the exhaust system connected and disconnected). And reading out all the DTCS, active and pending of course.
Re: swapping the o2 sensors
If it turns out you can’t swap both pairs of the o2 sensors for some reason, it might be possible to still swap one of the pairs. In other words the rear o2 sensors are a different part number and can’t be swapped, but the front ones might be the same part number. Also, there’s always the option of leaving the o2 sensors where they are, and swapping the cats. Big job, but you at least have it in your back pocket if you need to do it.
One other idea, the wiring from one of the o2 sensors to the pcm might be damaged & is causing the problem. There may be some way to the wiring harness for those sensors using a swapping method too.
So what would I do if I had this problem? I think the first thing I’d do is secure a lab o’scope and use it look at the pre- and post- o2 sensor output signals, comparing bank 1 to bank 2. I haven’t mentioned this as I doubt you have access to this instrument and probably have never used one before so you’d have difficulty interpreting what you were seeing.
Best of luck.
“I can put the car out for sale tomorrow and double my money.”
Why don’t you sell the car, in that case?
You’d have doubled your money, and the emissions problem is gone, and you could buy a car with no check engine light illuminated
Just tell the buyer about the P0420 code and the “eliminators”
no disrespect intended
In all honesty, I did once use a spark plug non-fouler (extender) on the rear O2 sensor to clear a p0420 once. I only planned to keep the car for another year before junking it (it was at its end of life). It cost less than $10, had no affect on engine operation, and successfully cleared the light.
If the car is not a junker that you’re band-aid’ing to keep going, it’s worth trying to fix properly.
OP writes …
Yes i hooked [the mil eliminators] to the rear o2 sensors. Its supposed to trick the computer into thinking everythings ok. Like it gives a steady signal or something like that
No experience with those, but the way the engine computer checks the cat operation is by comparing the voltage from pre-cat O2 sensor to the voltage from the post-cat O2 sensor. The O2 sensors are sort of like little batteries, who’s voltage changes with the amount of O2 in the exhaust stream. The ECM is trying to inject just enough gas to burn all the O2, but not so much gas that raw fuel (HC’s) comes out the exhaust. The problem is the ECM only has access to the O2 level, not the HC level. So getting the O2 level as low as possible (consistent with the mixture goal, neither over-rich nor over-lean) but not so low that HC’s come out, it’s a tricky business.
So the only way the ecm has to set the mixture, it injects a little more gas until the O2 stops going down, then it injects a little less gas, until the O2 starts going back up. It’s a never-ending process, the O2 goes down, then it goes back up. Over and over.
The ECM, as far as mixture control, it’s looking only at the pre-cat O2 sensor as it does this. So the output of the pre-cat O2 sensor, if you could look at it charted out vs. time, it would be going up and down several times per second. The post-cat O2 sensor voltage output mirrors what the pre-cat does. But less so. By this I mean the ups are not as high, and the downs are not as low. It’s like a filtered version of the pre-cat waveform.
As the cat’s performance degrades, the post-cat O2 sensor waveform starts to look more and more like the pre-cat’s. A defunct cat will produce a post-cat O2 waveform with higher highs, and lower lows than a good cat. In fact if you removed the cat, both the pre-cat and post-cat waveforms would look close to exactly the same. And that comparison is how the ECM determines the cat is on the fritz. When the post-cat waveform starts to look too much like the pre-cat, P0420 is the result.
You could imagine a clever circuit designer could design a circuit which would make the post-cat voltage waveform appear like the cat was working correctly. I presume that is the method your devices are supposed to work. But it’s also possible the car’s designers are even smarter than whoever designed your mil-eliminators, and have anticipated someone might try to do this, so have included add’l tests do determine if either of the O2 sensor paths has been tampered with. That wouldn’t take a rocket scientist to figure out either. It’s spy-vs-spy, a sort of cat and mouse game.
BTW, I’m not condoning the use of these devices. I like to breath clean air. But I could see how something like that might come in handy as a debugging technique.
GeorgeSanJose: great explanation…
Sorry I didn’t get back I got really busy and forgot to update y’all. @db4690 it’s a convertible and I wanted to enjoy it for at least most of the summer. Plus with no check engine light and an inspection sticker, it’s worth closer to 3x what I paid for it. A friend of a friend took a look at the exhaust and he believes one of the o2 sensors is faulty. I ended up swapped the mil eliminators side to side figuring one might be bad, made sure the connections were clean and the light never came back on. After 150 miles I had autozone hook the scanner to it, no codes came up and all the monitors were ready. Took it for inspection and passed no problem.