Car question

[tw]

Originally Posted by Clodfobble

Is the evidence a trail of money? Because I could follow that, and then fix anything.

In string theory, we believe reality has 11 dimensions (not to be confused with the twelve taught in AA meetings). Money is a low level domain where the most corrupt cut throats to collect cash. Higher level diagnostics and equipment reside in a dimension where Dollars never appear in diagnostic error codes.

Raise yourself from a dimension dominated by business school graduates and other primitive species. All praise the gods of math and science. All chant verses of logic.

[xoxoxoBruce]

Originally Posted by tw

If you need new converters, then an engine defect caused premature converter failure.

Several forums mention this as one of that model's weak points... a common occurrence.

[regular.joe]

Originally Posted by tw

In string theory, we believe reality has 11 dimensions (not to be confused with the twelve taught in AA meetings). Money is a low level domain where the most corrupt cut throats to collect cash. Higher level diagnostics and equipment reside in a dimension where Dollars never appear in diagnostic error codes.

Raise yourself from a dimension dominated by business school graduates and other primitive species. All praise the gods of math and science. All chant verses of logic.

Are we talking about a car here? Cause if we are, you have just blown my teensy brain for the day. I should have had another cup of coffee before I read that. DAMN YOU TW!!!!!

[BigV]

Originally Posted by Clodfobble

Yeah, it was eight years old this past January, and has almost twice that mileage. But I've decided I can afford the diagnostic, and if they tell me I need new catalytic converters, I'll just tell them no and start figuring out how to wreck the thing for an insurance payout.

this is a good plan.

[Clodfobble]

Wellll... looks like it might have to be my plan after all.

It definitely is the catalytic converters failing. Both failed at the exact same time? Yes, because apparently what happened is the one failed, and then the added strain on the other was too much for it to bear so it failed very shortly after.

So! I have new questions to be answered by knowledgeable people who aren't automatically inclined to get me to pay them.

1.) He says that while replacing both catalytic converters would be about $2000 all told, he can replace them with "universal" (i.e., off-brand) parts for a total of about $600. BUT, there is no guarantee it will work for any set period of time, or even at all. He hinted that this would really only be the option to pursue if we wanted it to work just long enough to sell it. But there is a chance that they could put them on, they would be completely nonfunctional with our vehicle, and we would be back where we started but $600 poorer. What are the chances these "universal parts" will indeed work with a 2003 Mazda MPV, for whatever length of time?

2.) He says that while we can continue to drive with it the way it is for some length of time, it won't be a steady decline into failure. The exhaust will get thicker, and the mileage will get worse, but then at some point in the possibly near future the house of cards will fall apart and I will suddenly only be able to go about 10-15 miles per hour. This doesn't sound to me to be the way a failing engine would work, but I know jack shit about it. Is this correct? Because I can deal with gradual, I can't deal with the engine giving out on me in the boonies halfway between here and Houston.

[glatt]

I had a friend years ago who had a similar problem. This was in a state with no emission testing at the time. Her cat also failed to the point that the engine wouldn't run properly. The cat was basically plugged and wouldn't let the exhaust through. So a mechanic told her he could poke holes with a screw driver through the guts of the converter to allow the exhausts a pathway through. This was illegal and allowed the exhausts to completely pass through the converter without being treated. Bad for the environment, but she got a few more years out of that car.

I doubt you could find a mechanic willing to do that for you, and it would only buy you enough time to make it to your next emissions test, where they might prosecute you when they see what you've done, but it's probably not all that hard to do yourself. Understand that I'm not recommending this, just relaying a story.

[BigV]

hm.

I'll tell you what I know about catalytic converters, Clodfobble. See if there's something there for you...

The catalytic converter is aptly named, it uses a catalyst, notably platinum, to convert substances in the exhaust stream to less toxic substances. The platinum, and other magical chemical stuffs, aren't consumed by this process, just used like eeensy weeensy chemical tools to rearrange the compounds flowing past. Mechanically, a catalytic converter works like this: take a double handful of drink stirrers, the hollow kind, and wrap your fingers and thumbs around a large bundle. Now, pick up the bundle and look through it. Weird, huh? It's like a straw of ten thousand tubes. Your catalytic converter is like this, but with tinier holes, and lots more of them. The surface of the straws are coated with this catalytic compound. The whole thing looks like a brick, except along the axis of the "straws", through which the exhaust flows. This "brick-thing" is contained in a kind of can with the exhaust pipe running in one end, through the cat, and out the other end.

When the exhaust gasses heat up the cat to the normal running temp, the chemistry does its magic, making the exhaust less toxic. That's when things are running right. But, naturally, things can go wrong. There are a couple MAIN ways a catalytic converter can fail.

It can be ruined chemically. One easy (well, used to be easy, now it's harder, but you get the idea) way is to run a tank of leaded fuel through the car. The car will probably be ok, but it will poison the catalytic converter. It's a goner. The lead ruins the surface so the chemistry doesn't happen. The car will run fine, but the emissions will be bad. There are other ways to degrade the cat too, if your car is burning a lot of oil, that can crap it up too. So, you can foul up the cat chemically (pun intended).

You can also ruin a catalytic converter mechanically. That "bundle of straws" I was telling you about? In the cat, they're made of ceramic, like your.. well, I don't know what it's like. but the upshot is the thing is FRAGILE. And it is impervious to heat, that is, you can't melt it, and "send it down the tailpipe". If it gets broken anywhere, even a little, it will crumble, maybe slowly, maybe all at once, and you will have a MECHANICAL obstruction to your exhaust flow. This, as you may well imagine, is bad. This is (probably) the "plugged up" scenario you heard. I can hear a failing catalytic converter, they have a distinctive tinkling sound at low speeds. That is from the ceramic element rattling around in the metal box that contains it. When they're new, they are neatly, and tightly fitted inside the box (it could be many different shapes, box, cylinder, tube, lozenge, etc, whatever). As the car is driven, and it gets shaken around, it's possilble that this ceramic honeycomb gets rattled around and maybe knocked loose a little. Imagine it's still in there, but knocked around some, so that the corners are rounded a little. Now it just sits in the can, which is fine, but it's a ceramic "brick" sitting in a sheet metal "can" attached to the exhaust plumbing. It's gonna rattle. That's what I can hear, you could hear it too.

Anyhow, the cat that comes with the car is designed specifically for that car in lots of ways. Like, where it connects, how hot it will get when the engine is running normally, how much flow it can accomodate, how much catalyzing surface area is available to the exhaust, etc etc etc. Your "universal" one isn't designed with these specific parameters in mind. It likely has the same chemistry setup, but will it be hot enough? too hot? too restrictive? too "loose"? etc etc etc. These are the kinds of unknowns that give the mechanic pause regarding the efficacy of the universal parts. I think the chance that the universal units would NOT WORK AT ALL is low. Unless they're like, mock ups or some other nonsense. I think you could just BYPASS the flippin converters all together and the car would still run, but you'd be passing untreated emissions. But the car would run.

Does this help?

[Lamplighter]

V: Once that catalyst is destroyed, doesn't the exhaust develop a really stinky smell.

I've been behind cars that had such a stinky exhaust,
and I humored myself by thinking it was a bad converter.

[BigV]

Could be. ??

Stink is often sulfur, and I associate sulfur with diesel, not gasoline, but certainly, if you're not treating the exhaust as designed, there could be such a side effect.

[tw]

Originally Posted by Clodfobble

It definitely is the catalytic converters failing. Both failed at the exact same time? Yes, because apparently what happened is the one failed, and then the added strain on the other was too much for it to bear so it failed very shortly after.

That type of failure means one converter failed months earlier. And the oxygen sensor only for the failed converter was reporting that failure long before a second converter failed. You did not report those those symptoms.

To have both converters fail so quickly requires something that causes complete damage in maybe one day. For example, contaminated fuel that permanently damaged both converters.

A catalytic converter simply burns gasoline that an engine did not. Converts unburned gasoline (and other pollutants) into nitrogen, oxygen, water, and other non-pollutants. A failed converter does not reduce gas mileage. It just stops converting gasoline, et al to non-pollutants.

Only way a converter can reduce mileage is to collapse and restrict exhaust flow. This becomes obvious from a noticeable reduction in acceleration and decidedly changed engine noise. Two converters do not fail within the same hour. I would get a second opinion.

What will a mechanic do when changing a converter? Automatically replace oxygen sensors that might be defective. Then the vehicle owner can only assume the mechanic was correct.

A P0174 error code is unrelated to the converter. Implies an engine problem; not a converter failure.

The vehicle is a six cylinder engine. Usually, two converters mean one for three cylinders with no connection common to all six cylinders. If all cylinders connect to a common pipe, then much less expensive is to design one converter for all six cylinders. All six cylinders connected to both converters leaves me suspicious. A third reason why I have trouble with his conclusions.

What happens when one oxygen sensor fails? It reports a too lean mixture. So the engine dumps too much gas into cylinders and converters. While dumping maximum gasoline into the engine, a failed oxygen sensor still reports “too lean” - error code P0174. A resulting overheated converter fails due to burning too much unburned gasoline. I don’t believe this is your problem. But it is another example of what better describes your symptoms.

[ZenGum]

Big V - excellent description.

Lamplighter - stinky exhaust can also be a car running on LPG or even biodiesel.

TW - yeah, that bit about one cat failing thereby "putting extra strain on the other"... assuming they're parallel, this makes no sense.

But could they be serial?

Come to think of it, probably not, because it doesn't explain the LH and RH codes. Ideas, anybody?

[Clodfobble]

Originally Posted by tw

And the oxygen sensor only for the failed converter was reporting that failure long before a second converter failed. You did not report those those symptoms.

Which symptoms was I supposed to report? My check engine light was not on prior to this episode. It was running fine; still is.

In fact, the check engine light has not yet come back on, since it got shut off yesterday after the diagnostic. I'mma keep waiting...

[Lamplighter]

Originally Posted by Clodfobble

Which symptoms was I supposed to report? My check engine light was not on prior to this episode. It was running fine; still is.

In fact, the check engine light has not yet come back on, since it got shut off yesterday after the diagnostic. I'mma keep waiting...

Think horses, not zebras.

If your mechanic reset the check engine light and you are driving with "good" gas,
I'll suggest that both converters did NOT fail at the same time, or at all.
Instead it was a loose gas cap or something like that.

If the check engine light comes back on right within just a few miles, that's one thing,
but if it stays off for a longer, I suggest it's your mechanic that is failing.

Get a second opinion, or third, from a reputable establishment.
.

[Clodfobble]

Yeah, when the other guy shut it off for me on the sly, it came back on within 2 days I think. So we'll see. I'm certainly not having any work done on it if the light stays off.

I also went ahead and ponied up for a guy at justanswer(.com.) Basic freelance expert site, about $18 for a conversation as long as you need it to be, I've had success using them before. Anyway, he said yes, the catalytic converters in a Mazda MPV are in parallel, but if one is mostly plugged up, then it will cause exhaust to back up into the engine and thus be forced by pressure into the other one, leading to the "added strain" effect. He said it was kind of unlikely, since the parts are the same age, it's not like I have one terrible one and one that's fine, unless maybe one sustained damage at some point (which is possible, I did go over a really violent pothole over the summer that knocked my alignment way out of whack.)

He noted, however, that there are also two O2 sensors, and one wouldn't affect the other, so even if it is actually sensor issue we're still looking at two sensors going bad at the same time (which is pretty much the issue tw noted, except instead he accused me of not mentioning that the first O2 sensor must have been failing months ago. ) He said the only other possible thing that might cause these codes is an exhaust leak somewhere up the line that might be confusing both O2 sensors, though he said again this would generally cause a sensor code, not a converter code.

[tw]

Originally Posted by Clodfobble

Which symptoms was I supposed to report?

If a first failed converter put extra strain on the second, then you reported a failure of the first converter a month plus ago. A second converter failed only recently. As I said, those are the symptoms you were supposed to report if the mechanics diagnosis was accurate. You did not report those symptoms.

You did report symptoms that, for example, report a failing oxygen sensor. It was probably first failing as much as a year ago. Could have been seen long ago by a computer attached to the diagnostic ports. But only recently got bad enough to cause an error code. Do not confuse that oxygen sensor with others on the converters - which, in hindsight, I believe you and others were doing.

Meanwhile, the mechanic's analysis (bad converters) do not explain error code P0174.

An intermittent error code implies your always existing failure is slowly getting worse. Or only gets reported when detected in consecutive engine restarts.

Furthermore, error code P0174 may not cause a check engine light. May be detected repeatedly by the engine computer. But only reported on its diagnostic port.

Some designs have a ‘diagnostic plug’ that, when attached, causes unreported error codes to appear as a flashing check engine light.

Driving conditions (and even different gas) may cause a marginal problem to be worse. Always there and detected by monitoring numbers from various sensors. Those codes can be created by a long list of possible suspects. Blaming two failed converters was way down the suspect list.

Suspect list could be shortened significantly by monitoring numbers from various sensors, as noted above. But you cannot do that without a maybe $120 computer that plugs into every car's computer (ie Car Chip). Check engine light can be cleared by that layman’s tool, or sometimes by a ‘diagnostic plug’.

A least expensive solution is to watch this problem. Wait for it to become so obvious that any mechanic can fix it the first time. However if a check engine lights repeatedly, then fix it now to avoid possible future engine damage.

I suspect a P0174 error code still exists. That error code, alone, does not trigger a check engine light. But my wild speculation is based only in experience - not in facts required from the shop manual. Speculation is best anyone here can do without further information from that plug-in computer (sold even in Sears and Wal-Mart) and from a shop manual.

Your best suggestion is in a paragraph that starts, "A least expensive solution ...". I, on the other hand, have a nasty habit of doing things on cars that also exposed Saddam's WMDs and Tokyo Electric's lies about Fukushima. Ruthlessly, finding numbers and irrefutable facts (that explains all three error codes) requires information currently not available.