Mazda 6 Forums banner

Normal operating cat temps?

3K views 16 replies 5 participants last post by  KirkSwag 
#1 · (Edited)
LONG STORY SHORT ;)

My check engine light is on for 421 and 431. Ive suspected it was the cats and not the O2 sensor. My cats have never gotten red, glowed or had any issues with sputtering like they describe when its clogged. Exhaust has pressure when I put my hand over the tailpipe ends. Exhaust pipe temps are roughly the same throughout so it seems hot air is moving through just fine.

My problem is, I finally got around to saving some money to order the parts but I'm noticing my cats normal temps are 900 to 1200 driving to work (non highway) and from what I can tell, this is totally normal. When cats are clogged they are upwards of 1700 or so.

I think the guy before me gutted the cat to fix that issue but in turn still has the same CEL, just the engine wont blow itself up now.

actual question way down here
Best way to check this is remove the O2 and put a light in the bung and look for the honeycomb/mesh? I assume you can see it from the hole.
also was wondering if anyone had their normal operating temps for their cats?
(google yields 600 to 900 degrees and again 900 to 1200 degrees and again 1000 to 1600 all are normal for the Mazda 6 and well, im pretty sure thats not true :p and most of those cars had issues because the variance is too big)

Thanks!
 
See less See more
#3 · (Edited)
Thanks for the tag!
I am assuming in my OBD2 the cat11,cat21 and cattemp21 are before cat, after cat and the temp at the cat? I should of included my averages are 900 to 1200 with around town driving. (All 3 temps in my scanner are always the same, which is part of why im thinking I may not actually have precat material inside)
 
#4 · (Edited)
LONG STORY SHORT ;)

My check engine light is on for 421 and 431. Ive suspected it was the cats and not the O2 sensor. My cats have never gotten red, glowed or had any issues with sputtering like they describe when its clogged. Exhaust has pressure when I put my hand over the tailpipe ends. Exhaust pipe temps are roughly the same throughout so it seems hot air is moving through just fine.

My problem is, I finally got around to saving some money to order the parts but I'm noticing my cats normal temps are 900 to 1200 driving to work (non highway) and from what I can tell, this is totally normal. When cats are clogged they are upwards of 1700 or so.

I think the guy before me gutted the cat to fix that issue but in turn still has the same CEL, just the engine wont blow itself up now.

actual question way down here
Best way to check this is remove the O2 and put a light in the bung and look for the honeycomb/mesh? I assume you can see it from the hole.
also was wondering if anyone had their normal operating temps for their cats?
(google yields 600 to 900 degrees and again 900 to 1200 degrees and again 1000 to 1600 all are normal for the Mazda 6 and well, im pretty sure thats not true :p and most of those cars had issues because the variance is too big)

Thanks!
I seem to remember somewhere in the 700 range. The catalytic reaction speeds up when there is more fuel put in (rotten egg smell). Those P042/P0431 codes are given because your second (downstream) O2 sensors are inverting their signal too much. When an O2 sensor contacts an un-burned fuel it changes the voltage that it produces. When the changes in the downstream sensor oscillate like the upstream sensor the computer tell you that there is not enough catalyst to maintain a reaction.
If you dump fuel into the exhaust the converter will heat. If you dump too much fuel (poor ignition) the converter will overheat. When it overheats the catalyst matrix begins to break down.

I just had to replace a manifold last month because it broke free inside the housing and was shaking around as I drove.

Broken Walker catalytic converter 2004 Mazda 6 pre-cat making rattling sound
 
#5 · (Edited)
Rectangle Font Screenshot Electronic device Parallel
Font Screenshot Rectangle Parallel Multimedia

No smell from the back of the car at all thankfully, I do smell a little gas/exhaust when car first starts up but im fairly sure theres a small leak at a flange somewhere near the firewall thats hard as crap to get to.

and thats disconcerting, my temps are way over. My o2 sensors have always looked similar, oscillating like normal, all of them the same though. Low volts to about .8

Ill grab some forscan results on the way home to see how its doing. (Temps AND o2) Ill give it a bit more gas than I do in the early am, see if the temps raise higher as well.

Thank you for your input!
edit
Nice car by the way! Ive never seen another 6s wagon other than my own in real life :p
 
#6 · (Edited)
Font Screenshot Technology Electronic device Audio equipment
Font Screenshot Technology Electronic device Audio equipment
Font Line Screenshot Parallel Technology
Font Line Screenshot Audio equipment Technology
Font Technology Parallel Screenshot Electronic device


It wont let me upload the CSV or the zip of it. But yeah, my o2 sensors look off =/
This car, I swear to jeebuz, one thing after another :D (im sure due to previous owners shennigans)
With a bit of throttle and only 40mph I can hit 1400 with the cats, so it does seem to be letting gas through. I cant even think of how bad it is on the freeway or up long hills.

So it does seem atleast to me, the cats are most likely bad. This is too bad, the transmission is slipping randomly too, only once or twice a month. On a good note, I dont also need a new engine? =/

Thanks for the input!
 
#7 ·
When you say “no good,” do you mean no longer catalyzing efficiently, or do you mean semi-plugged in the sense of restricting exhaust flow noticeably more than ‘normal?’

How are your fuel trims?
 
#10 · (Edited)
Fuel trim is 1 and 2 in graph, they look pretty good to me but again, no expert. The graph shows cat temps, throttle, o2 and trim. I finally got the CSV to load into an awesome graph but did not realize the forum wont let me post those files, so I just copy pasted a section that showed all of the values. Low on both of -3.12 and a high of 3.91 for fuel trims. (yay, figured how to post the graph!)

It does look like too much fuel is going through, i believe the negative is when its retarding fuel

-2.34-0.78
-1.56-0.78
-1.560.00
-1.560.78
-1.560.78
-0.781.56
-0.782.34
-0.782.34
0.003.12
0.003.12
0.003.91
0.003.91
0.003.91
0.003.91
0.003.91
0.003.91
0.003.91
 
#8 ·
Your cats would overheat if your car is not burning the air/fuel mixture completely, or if they were clogged. If they are "no good" as in the catalyst is poisoned or otherwise not working, you would have lower post-catalyst exhaust temperatures than normal. The catalyst's function is to catalyze unburnt fuel and oxygen. This releases a lot of heat when it is doing a lot of this work. The EGTs downstream of the cat will usually be higher than upstream when the engine is under load.

Otherwise, if you have any concerns that you may have a broken or clogged catalyst, you really need to leave the car in the garage until you determine whether that is truly the case. It is a surefire way to destroy a motor. If the catalyst has actually clogged and not just disintegrated, then it will be very noticeable (significant loss of power). If it is disintegrating and going out the tailpipe, there is still a significant risk of your engine inhaling catalyst dust, but you would not see high EGTs in this failure mode.

I don't know if that will help but as I read this thread, it occurs to me that you may be going about your diagnosis wrong.
 
#9 · (Edited)
Your cats would overheat if your car is not burning the air/fuel mixture completely, or if they were clogged. If they are "no good" as in the catalyst is poisoned or otherwise not working, you would have lower post-catalyst exhaust temperatures than normal. The catalyst's function is to catalyze unburnt fuel and oxygen. This releases a lot of heat when it is doing a lot of this work. The EGTs downstream of the cat will usually be higher than upstream when the engine is under load.

Otherwise, if you have any concerns that you may have a broken or clogged catalyst, you really need to leave the car in the garage until you determine whether that is truly the case. It is a surefire way to destroy a motor. If the catalyst has actually clogged and not just disintegrated, then it will be very noticeable (significant loss of power). If it is disintegrating and going out the tailpipe, there is still a significant risk of your engine inhaling catalyst dust, but you would not see high EGTs in this failure mode.

I don't know if that will help but as I read this thread, it occurs to me that you may be going about your diagnosis wrong.
Could be, if I knew what I was doing It'd be fixed :p Only time ive dealt with a cat was years ago and I just paid to have it replaced. (it had broken and a piece fell and obstructed exhaust to the point the car wouldnt move-easier to diagnose ;) ) I dont really know how to test a cat, this car has so many problems I get to learn all kinds of things. So I figured I would visually look to make sure the mesh is in place, if it is go from there. I didnt think it was obstructed as the temps dont have any major hotspots or restrictions when checking with a temp gun.

The cars been like this since I got it, I didnt realize the check engine light was on until one night I noticed there was no check engine on start up(I should of realized earlier but, entire dash was dim), after I fished all the plaster of paris out of the instrument cluster so I couild see the light, this fun repair journey started, but, about 8 months ago, this is the last few codes I need to clear. Car no start, electric and similar I can do fairly well but a cat, biggest tests ive done are heat, check for obstruction for flow out the tailpipe and visual inspect.

With the cats people tend to argue its the o2 sensor or something else fairly often, so just trying to get all my ducks in a row before the weekend. Car seems to have normal power and get up and go, unless the transmission decides to not shift for a second before lurching. (another issue that I didnt notice until after the test drive due to him putting who knows what in there)







When you say “no good,” do you mean no longer catalyzing efficiently, or do you mean semi-plugged in the sense of restricting exhaust flow noticeably more than ‘normal?’

How are your fuel trims?

Will check fuel trims on the way to work. and I say no good, it doesnt seem normal to go from 900 to 1500 in temp without much effort/throttle, most of what im reading that doesnt look good. Could be more unburnt fuel making it through, Id expect some other code, or would hope for one. Either way will report back with fuel trims in a few hours!

Im going to be replacing the valve gasket, pcv, a few other gaskets, 2 heater hoses and another connector this weekend so figured this would be the best time to tackle that project as well since so much will be out of the way.
 
#11 · (Edited)
@KirkSwag I took some temps today with the engine idling and radiator fans turning. I read 330 degrees F just below the O2 sensors.

As for the shifting, I had that too and solved it by draining the trans fluid and replacing it. I ran it a bit then drained it again and replaced. I did that for a total of 3x. From that point on I drain and refill every 30,000 miles as maintenance.

Just because the catalyst matrix is still present does not mean that it is flow compromised. I have been on here for a few years and this issue comes up often. Everyone always want to believe it is the O2 sensors but the older the sensor the slower it reacts and the less likely it will report a P0421/P0431 code. It certainly does not hurt to replace them because they have a service life of 100,000miles and will need to be replaced with the manifold converters anyhow, (at least the upstream ones for proper fueling)
 
#12 ·
Thank you for checking!

Was this the o2 in the front or underneath the middle?
I had checked the front, I get 550 on the bung of the o2, 400 on the first shield directly around it and 180 on the shield slightly further down.

I went ahead and ordered some oil, air filter, oil filter, spark plugs, valve cover gaskets (its leaking on the front right) some more hoses in random sizes just incase for just regular upkeep. Ill be able to get some transmission fluid on Friday, if it helps with that I may as well try. Do you have a suggestion for the trans fluid?

Bringing my thread back on topic :D other than o2 which usually seems a wish and a dream, are there some more common reasons for it to throw this code that isnt the cats? Ive been googing a ton, just started on this issue as it seemed the most expensive so I saved it for last. At worse after I figure how to test and confirm I can give them a go, the front doesnt seem that bad, the rear I havent looked at.

Thanks again
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top