mmo and failed cat?

[k24a4]

I recently had the catalytic converter replaced on my '04 accord at the dealership and fortunately for me, under warranty, as the car has 74800 miles on it, after 8 months or so of an intermittent cel, code p0420. Every time I set an appointment, the light would go off. Finally, I got to the dealership with the cel on and to their credit they replaced the cat without a fuss.

Coincidence or not, I began using mmo at the recommended dosage in the fuel within the last year as a preventative and for its ucl properties, as advocated by some here. I have had no other issues with the car, and it is maintained by the book. Now, I can't prove that the mmo caused the bad cat, but it has certainly made me question the continued use of it in this application.

The only other abnormal thing to happen to the car is that a few years ago I ran the car for ~2 miles with a paper towel caught inside the air intake baffle (don't ask), so the rpm's shot up to 3-4k and the car struggled mightily to accelerate before I figured out what was wrong and headed back to the house trailing the stench of rotten eggs behind me. Fortunately, although ripped, the paper towel was extracted whole from the intake. Within that short period of time where the ecm I'm sure was frantically trying to sort out the a:f ratio, is it possible that unburned fuel got to the cat and degraded it? My understanding is that fuel on the converter substrate is like water on cotton candy: it bores right through.

So, just thought what others might think. I'm glad I got the converter replaced under warranty, but I've also chastised myself for being an idiot in the last instance with the paper towel, and perhaps the first one involving mmo.

 

[sciphi]

I'd lean to the paper towel instead of MMO use. Lots of folks use MMO with no trouble. Then again, you could be the one in a million...

 

[hardcore302]

I have had no problems. It could be failing for a few reasons. Tough to really nail it down.

 

[sunfire]

How does a 6+ year old car with nearly 75K miles still have warranty on any parts?

 

[Lethal1ty17]

if mmo caused a significant number of cat failures by now, we'd know. its been around for the larger portion of a century, and cats have been around for probably 30 years of that. like you said, you have no proof that it caused it. on the flip side there isnt any proof that it didnt cause it, but it is very unlikely to do so. sometimes you just get faulty parts, it happens, but raw fuel in a cat isnt ideal.

 

[stang5]

Originally Posted By: sunfire
How does a 6+ year old car with nearly 75K miles still have warranty on any parts?


emission systems have a longer warranty coverage...

 

[demarpaint]

My E-150 has been fed MMO since 1988 give or take, it still has the original CC. 1993 Aerostar with ~190K miles on it has been feed MMO for close to 135,000 miles now. Original CC and 02 sensor. I had an 85 E-150 that was fed MMO for over 150,000 miles and sold with the original CC in it.

I started my 08 Jeep on an MMO in the gas diet when it had about 300 miles on it IIRC. No problems to report in close to 3 years of owning it.

It could be a fluke, or a defective CC was installed the second time. I ran some pretty strong doses of MMO from time to time as well.

 

[Kaboomba]

Originally Posted By: k24a4

The only other abnormal thing to happen to the car is that a few years ago I ran the car for ~2 miles with a paper towel caught inside the air intake baffle (don't ask), so the rpm's shot up to 3-4k and the car struggled mightily to accelerate before I figured out what was wrong and headed back to the house trailing the stench of rotten eggs behind me. Fortunately, although ripped, the paper towel was extracted whole from the intake. Within that short period of time where the ecm I'm sure was frantically trying to sort out the a:f ratio, is it possible that unburned fuel got to the cat and degraded it? My understanding is that fuel on the converter substrate is like water on cotton candy: it bores right through.


I think the paper towel incident did it. Here's how I see it:

1. Paper towel severely chokes engine
2. ECM tries to satisfy acceleration demand (foot on go-pedal)
3. ECM defaults to full-rich, and possibly (most likely) spews unburned fuel out of the exhaust valves and into the cat
4. In the cat, air is actively pumped in as part of its normal function of converting "bad" stuff to "OK" stuff
5. The unburned fuel burns IN THE CAT, aided by the air from the air pump
6. The fuel burning uncontrolled (probably sort of weak and dirty) in the cat consumes most of a lifetime supply of platinum in just a few minutes
7. Over the following months you consume the rest of the catalyst in normal driving
8. When the cat is completely used up, you get a CEL+code

Eh?

 

[rslifkin]

If you had a rotten-egg stench after the paper towel, that means it was running very rich, and probably overheating the cat. Chances are, that's what did the damage, and it just took time for it to show up.

 

[J. A. Rizzo]

Originally Posted By: Kaboomba
Originally Posted By: k24a4

The only other abnormal thing to happen to the car is that a few years ago I ran the car for ~2 miles with a paper towel caught inside the air intake baffle (don't ask), so the rpm's shot up to 3-4k and the car struggled mightily to accelerate before I figured out what was wrong and headed back to the house trailing the stench of rotten eggs behind me. Fortunately, although ripped, the paper towel was extracted whole from the intake. Within that short period of time where the ecm I'm sure was frantically trying to sort out the a:f ratio, is it possible that unburned fuel got to the cat and degraded it? My understanding is that fuel on the converter substrate is like water on cotton candy: it bores right through.


I think the paper towel incident did it. Here's how I see it:

1. Paper towel severely chokes engine
2. ECM tries to satisfy acceleration demand (foot on go-pedal)
3. ECM defaults to full-rich, and possibly (most likely) spews unburned fuel out of the exhaust valves and into the cat
4. In the cat, air is actively pumped in as part of its normal function of converting "bad" stuff to "OK" stuff
5. The unburned fuel burns IN THE CAT, aided by the air from the air pump
6. The fuel burning uncontrolled (probably sort of weak and dirty) in the cat consumes most of a lifetime supply of platinum in just a few minutes
7. Over the following months you consume the rest of the catalyst in normal driving
8. When the cat is completely used up, you get a CEL+code

Eh?


I don't think his car has an air pump for the cat, and the ECU would only go full-bore on the fuel delivery rate if the O2 level and MAP/MAF were high. Presumably with a clog in the intake, these would be low, but the ECU can only trim the fuel back so far while the TPS beckons for more speed. That's probably where the excess fuel made it to the cat, but there it accumulated until the exhaust O2 level came up (coasting?). But if there was a rotten egg smell during this event, the converter was probably already somewhat fouled and the incineration was just icing on the cake (or water on the cotton candy). If the burning tore it up, it would probably shatter at some point and you would hear rattling.

Did MMO do it? Who knows? Should you quit the MMO business? IMO yes, but that's only because I haven't heard of any quantifiable benefits that would justify 1) expecting a system not designed to handle this chemical to burn it cleanly and trouble-free and 2) the added cost and complexity to the car ownership experience. Sure, people haven't reported many problems doing it, but I haven't heard many noteworthy benefits either.

 

[Familyguy]

I doubt MMO had any hand in the failure. Catalytic converters have a finite service life. While 74k is short, it's probably within a standard deviation or two of the mean for typical cat life cycles. They covered it because it is within the federally mandated time frame for coverage on emissions-related parts.

I'd place this firmly in the "shiznit happens" category.

 

[Trav]

Very doubtful MMO had anything to do with it.
Over the years I've seen lots of cats go bad for lots of reasons and some for no apparent reason at all.
2006 1/2 ton pick up with 32k ran fine one day and the next day
it came in on a hook,bad cat.Replaced under warranty no codes,fuel trim normal,now over 100k with no subsequent cat failure.

I would say between the MMO and paper towel i would take the towel as the primary culprit.

 

[Spazdog]

I have a pre-06 Mazda 6S, I have the sketchiest pre-catalytic converters in the world and MMO has done nothing to them.


...but thanks anyway. Now I'm going to worry about it.

 

[Spyder7]

Agree with the other posters who indicate its extremely unlikely MMO had anything to do with it, for the same reasons given. Also Marvel states on their site it is safe in fuel for emissions systems, sensors, etc. They hold themselves open to liability issues if that statement was false, and not being snake oil peddlers or some fly by night outfit, I take that claim as being legitimately made.

-Spyder

 

[cronk]

Originally Posted By: sunfire
How does a 6+ year old car with nearly 75K miles still have warranty on any parts?


Federal emissions law says manufacturers must cover cat converters and ecm for 8 years or 80k, whichever comes first.

 

[CharBaby]

k24a4, was your cat leaking or plugged? Most/all cat's have an 8/80K warranty. Honda's may be even longer. Some Honda's are warranty'd for 14 years " Beleive it or not ". I read the posted letter in a local reputable muffler/brake repair shop.

I replaced the cat under warranty in my wifes 2001 Lexus in 2006(5 yrs old) due to rotting on the weld on both sides of the hanger, where it's welded to the pipe going to the cat(all one unit). This one unit consisted of everything except the SS flex pipe on one end and muffler at the other. This consisted of(pipe, cat, pipe, resintor, pipe)all one piece. $1300. It too was throwing a code. Nothing really wrong with the cat itself but, where the pipe had rotted was just before the downstream O2 sensor and "it" was causing the poor performance, poor mpg and engine code. But the catalitic converter itself was actually fine internaly.

I have driven vehicles with plugged cat conv's and they run terrable...No power even if they start well. Can't get the vehicle to run past 20mph.

 

[sunfire]

Originally Posted By: cronk
Originally Posted By: sunfire
How does a 6+ year old car with nearly 75K miles still have warranty on any parts?


Federal emissions law says manufacturers must cover cat converters and ecm for 8 years or 80k, whichever comes first.


Thanks. Didn't know that.

 

[k24a4]

Originally Posted By: Char Baby
k24a4, was your cat leaking or plugged? Most/all cat's have an 8/80K warranty. Honda's may be even longer. Some Honda's are warranty'd for 14 years " Beleive it or not ". I read the posted letter in a local reputable muffler/brake repair shop.

I replaced the cat under warranty in my wifes 2001 Lexus in 2006(5 yrs old) due to rotting on the weld on both sides of the hanger, where it's welded to the pipe going to the cat(all one unit). This one unit consisted of everything except the SS flex pipe on one end and muffler at the other. This consisted of(pipe, cat, pipe, resintor, pipe)all one piece. $1300. It too was throwing a code. Nothing really wrong with the cat itself but, where the pipe had rotted was just before the downstream O2 sensor and "it" was causing the poor performance, poor mpg and engine code. But the catalitic converter itself was actually fine internaly.

I have driven vehicles with plugged cat conv's and they run terrable...No power even if they start well. Can't get the vehicle to run past 20mph.


I don't believe the cat was plugged. Acceleration and general performance were fine. My gas mileage dipped by 1-2 mpg, though. The bottom heat shield did fall off, however, just before the check engine light came on the last time, so, yes, the bolts were rotted away. I did not meet with the tech to ask him about the condition of the converter itself. The rest of the undercarriage is pristine; I wash and wax regularly.

I went to the dealership armed with the federal emissions warranty of 8yr/80,000 miles, and I also knew the code the ecm was throwing (P0420), but I kept my mouth shut out of the gate and was pleasantly surprised when the service writer gave me the news that I would incur no cost for the converter replacement. I don't go to the dealership often; I do oil changes and routine maintenance myself and it is, after all, a Honda, so I wasn't sure what to expect, knowing it could be a major repair in terms of cost. The dealership service experience was needless to say very, very, good so I promptly wrote up a positive review on 'yelp'. They will certainly be first in line should I need a new Honda.

Thanks for the responses. I'm going to stop the mmo for now to get a baseline mpg with the new cat, and then I may resume. It was because of all the interesting info here that I started mmo in the first place.

 

[Vikas]

Who is this Honda dealer in MA?