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Strategies to keep cats from melting

tosha

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The way I understand it,
The front O2's has a rich/lean switching rate that is directly from the engine operating conditions. Easily seens in the lamba PID. It changes rates with load and RPM. This switching rich/lean "depletes and fills" the catalyst of stored oxygen. Oxidation and reduction cycles of the three catalyzed reations.
To test the catalytic converter, they are concerned with its oxygen storage capacity. below a threshold of oxygen storage, and it gets reported as failed/ ineffecient.

To test this, steady state conditions need to be meet for long enough to run a test with fuel being controled by the rear O2 sensors. Theres a few steps and it will abort in the middle of any of them if conditions are not maintained.

When it controls fuel from the rear sensors, the switching should be slower the more oxygen the catalyst can store slowing the oxygen signal(transport delay) from reaching the sensors, so they overshoot lambda more than the fronts would. If this overshoot isn't enough, the catalytic converter is considered failed/ ineffiecent.

Attached is a picture of what im talking about. When they start to fail/ become ineffecient the switching becomes less noticable in the logs. Probably best to just wait for a MIL light and let the ECU do its job, rather than comb logs looking for early signs, which would actually be harder to notice the more ineffecient the catalytic converter becomes.

Of course if its temperature related and melting failure, you probably wont see signs of it in a log until after it happens and the car sounds, smells, and runs bad. Some failures they will crack first, then melt, but as far as I know when they melt, its quick with out advanced warning.

Catalyst test.jpg
Thanks a lot. The problem that I have is that I started getting P0430 errors, but my dealer keeps insisting that these are tune ralated and they are working with Roush on analysis and getting an updated tune from them. One update that they installed recently did not really fix anything. As long as the cat is not melted and I don't end up with a failed engine, I'm ok to let them figure it out. Thinking about it more, it seems that datalogging won't help me much, as it would show same conditions that already lead to CEL. What's the best way to inspect physical condition of the cats? Does it make sense to get one of these inspection cameras and use sensors holes to do a visual inspection? I want to double check what I'm hearing from the dealer.
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tosha

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See post #65 in this thread.
Thanks! That helps, but guess my question was more about operating conditions during the test. Should I be doing it while on cruise control going at certain rpm, or just driving around, or logging at idle while car is stopped? Any other things to take into consideration?
 

engineermike

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The problem with just looking at the rear sensors at any point in time, is they are not in control of the fuel and therefore the oxygen stored in the converter. When the fronts control the fuel, its much much faster than the rears can display, and so the rears show rich from the lack of oxygen, when really its just been bouncing around stoich. Maybe if you start seeing the rears looking exactly like the fronts, but i'm willing to bet the monitor test catch it losing effeciency long before you see that….
You know the rears are narrows band right? They basically just toggle high/low, almost like a digital signal.

I’ve never tried to diagnose a bad cat before the pcm identified it, but twice I failed a cat and used rear o2 data to confirm. It’s pretty obvious when looking at steady state interstate-speed cruise.
 

engineermike

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... As long as the cat is not melted and I don't end up with a failed engine,…. What's the best way to inspect physical condition of the cats? Does it make sense to get one of these inspection cameras and use sensors holes to do a visual inspection? I want to double check what I'm hearing from the dealer.
The most recent cat I failed (and verified in log data) looked perfectly fine to the naked eye. These can degrade in ways that are not visible.
 

engineermike

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Thanks! That helps, but guess my question was more about operating conditions during the test. Should I be doing it while on cruise control going at certain rpm, or just driving around, or logging at idle while car is stopped? Any other things to take into consideration?
It’s most obvious at steady speeds in the 70 mph range.
 

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tosha

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The most recent cat I failed (and verified in log data) looked perfectly fine to the naked eye. These can degrade in ways that are not visible.
Understood. If it loses efficiency, but still maintains the flow and does not create a risk of engine failure, I would let dealer figure it out. I'm just looking to confirm that I can keep driving the car while they are working with roush on whatever the issue is.
 

engineermike

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When I installed the EGT sensors, my goals was to determine if the cat temp model was accurate. The data I got was not what I was expecting, particularly the high downstream temps in the ~1+ minute after going Wot. The temps being higher than inferred cat temp made me question the validity of the cat temp model (in ways I can not calibrate) and accuracy of my EGT.

Ive since swapped the EGT’s and got the same result. Plus the collector EGT looks very reasonable, so I am confident in the data.

Ive also talked the issue over with a chemical engineer and now understand that it is entirely possible for the downstream temp to be higher than the catalyst temp.

So, now that I have more confidence in the data and cat temp model, the question is “does my cat temp input data, particularly the engine EGT data, need further calibration?” I swapped out the Whipple EGT data for gt500 data, which is about 200 deg higher iirc. This seems directionally correct to me based on the number of Whipple cars failing cats. The gt500 data is higher/hotter than both Roush and Whipple, so it will trigger cat protect sooner. One might argue this is due to the compression ratio, but I would point out the relative frequency of failed cats on Roush and Whipple cars vs stock gt500’s.

One valuable learning for me was that my downstream EGT never exceeded about 1580 deg F, while the inferred cat temp was around 1680. This gives me some peace of mind that my inferred cat temp isn’t grossly wrong.

At the moment I’m only running 9-10 psi boost and 22 deg timing. I think I’ll re-check the EGT when I go back to 15 psi and 17 deg timing to see if it still looks reasonable. Then I’ll consider some strategy to run richer in PE to delay COT. It might be faster to run .72 all the time at wot rather than starting at .77 then going to .69 after a few seconds.
 

markmurfie

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You know the rears are narrows band right? They basically just toggle high/low, almost like a digital signal.

I’ve never tried to diagnose a bad cat before the pcm identified it, but twice I failed a cat and used rear o2 data to confirm. It’s pretty obvious when looking at steady state interstate-speed cruise.
Yes I know that, but we are talking about commanding stoich which both sensors can do feedback for. Other cars that have front narrow bands do the same and have the same diagnostic test principal as well. Wide band or narrow band, stoich is stoich. Switching lean/rich or rich/lean around stoich is a time transport delay that can be compared pre to post sensor, with an efficient cat slowing the switching of the post sensor causing an increased transport delay. I'm referring to looking at the transport delay time and it becoming exactly the same.

The second idea I posted is for monitoring different materials in the catalytic converters. Don't think our cars have that, but future cars may. It delays MIL tho so may never be used with standards getting stricter. MIL will come on sooner if the cat is removed, so maybe it will. Then If some one is interested in putting a wideband behind their car to monitor it. The MIL will just catch the cerium loss first most likely.

Load and RPM has a far greater effect on transport delay, than sensor location. Thats why when people say you need to add 50% to it for long tubes that move the sensor slightly farther away from the engine, just don't understand what transport delay is.
 
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ProChargerTECH

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I'm interested to hear of Procharged experience on cat temps. My car seems to run very cool, even hot lapping at the strip. Has anyone melted the cats with a P1X?
We used 6 thermocouples mounted in locations very similar to what @engineermike posted. and found the inferred temps to be way off from reality.

My personal experience has been, that ANYONE with ANY forced induction of ANY brand, that runs a car with cats that were not designed for forced induction and high HP, up to very high speeds (Like a long highway run)... will at some point, fail the cats. (and cross your fingers it doesn't take out the motor).

I don't want to get into an internet war (especially with people that might not be around supercharged and turbocharged cars on a daily). But its just facts... its not IF they will fail, its WHEN.

Anyone that says it can't happen, is either clueless or lying.


What shows in the log when they fail or start to fail? Inferred temp change or trims etc?
When the knock retard goes from 0 to 8 degrees of knock instantly, I knew the cats had failed and clogged the exhaust. (Which once we pulled them down, the drivers side was about 80-90% blocked and the pass side was about 60-70%)
 

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LSchicago

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We used 6 thermocouples mounted in locations very similar to what @engineermike posted. and found the inferred temps to be way off from reality.

My personal experience has been, that ANYONE with ANY forced induction of ANY brand, that runs a car with cats that were not designed for forced induction and high HP, up to very high speeds (Like a long highway run)... will at some point, fail the cats. (and cross your fingers it doesn't take out the motor).

I don't want to get into an internet war (especially with people that might not be around supercharged and turbocharged cars on a daily). But its just facts... its not IF they will fail, its WHEN.

Anyone that says it can't happen, is either clueless or lying.




When the knock retard goes from 0 to 8 degrees of knock instantly, I knew the cats had failed and clogged the exhaust. (Which once we pulled them down, the drivers side was about 80-90% blocked and the pass side was about 60-70%)
I limit my throttle bursts to 10 seconds, or just enough to get thru the 1/4. I have no desire to try to hit top speed in the car. Hopefully that helps them live longer. I need to keep the cats for emissions testing.
 

engineermike

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Interesting log today; I did a 50-135 blast and on the Whipple 3.625 pulley. I stated earlier that model seemed to overpredict the cat temp. Well that’s true to a point. On this log the egt and mid-bed cat temp rose all the way until I let off, getting up to 1625 deg max. This is short of the danger zone of 1680, but the bothersome part is that going into cat protect and running .68 lambda didn’t prevent it from continuing to rise. I was pretty conservative in tuning cat protect mode, so anyone running a Roush, whipple, or most aftermarket tunes can expect numbers even higher than this, not to mention for longer durations.
 

LSchicago

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Interesting log today; I did a 50-135 blast and on the Whipple 3.625 pulley. I stated earlier that model seemed to overpredict the cat temp. Well that’s true to a point. On this log the egt and mid-bed cat temp rose all the way until I let off, getting up to 1625 deg max. This is short of the danger zone of 1680, but the bothersome part is that going into cat protect and running .68 lambda didn’t prevent it from continuing to rise. I was pretty conservative in tuning cat protect mode, so anyone running a Roush, whipple, or most aftermarket tunes can expect numbers even higher than this, not to mention for longer durations.
Was this on E85 or pump? How much boost?
 

engineermike

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Was this on E85 or pump? How much boost?
This is pump 93, 1.7 load (~13 psi), and 15-16 deg timing. Normally my timing runs higher but on this pull the cams fell off their snap line and the timing started pulling from a lower borderline table. The retarded timing didn’t help any but most pump gas supercharged gen3’s can only manage about that timing anyway.
 

K4fxd

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The whole adding fuel to cool the cats seems a bit out of sorts to my mind. Sure the liquid fuel will cool from evap but won't the cat react the fuel causing the temps to rise?
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