[Yet another] how do we make cats live thread...

[engineermike]

In this 145. Greg Banish on Calibrating Vehicles, Compliance, and the Aftermarket - YouTube video, Banish discusses how going into DFCO/DFSO right after WOT does damage to cats. I've long said that I had my doubts that absolute temp is what is damaging our stock-style ceramic-substrate cats, and it appeared to be more thermal shock (mechanical damage) than degradation of the wash-coat due to heat. DFSO cuts off the fuel and as a result, pumps ambient air into the cats.

As a result, I started looking for ways to prevent DFCO/DFSO after going WOT. You might initially think to just disable it completely, but I think there are legit diagnostics and tests done (e.g. crank learn) during DFSO.

I found parameter auF41670 in PCMTec "Maximun inferred catalyst midbed gas temperature to allow reactivation of cat after a DFSO, avoid high temp lean" and tested it to determine if it would work. I don't think this parameter is defined in HPTuners.

This is using the OEM setting of 1750 deg F (Roush F150). The inferred cat temp never exceeded 1750, so DFSO kicked in as soon as I let off. You can tell because the Inj cyl 1 pw and fuel flow dropped to 0.

The inferred cat temp dropped 500 deg F in 9 seconds.

I lowered the 41670 parameter to 1350 deg F, and this is the result:

DFSO did not activate this time. You can see the inferred cat temp stayed steady or even rose a little and only slowly cooled back down.

Is this the silver bullet for OEM cat life? I don't know but I'm going to run it this way on one of mine and see how it holds up.

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[Mikepol2]

Do you have any speculation as to why the OEM values are what they are? If this parameter change can extend cat life, you'd think Ford would want to use it unless there are offsetting downsides to it.

 

[engineermike]

The factory cats on a stock engine don't seem to fail very often, so it seems to be set adequately for an unmodified car. I'm only speculating here but the heat loading from a supercharged engine is higher and the fuel loading into the catalyst is higher as well, so we may need some more "cushion".

 

[Grimreaper]

Nice find. I wonder what the gt500, hellcat and z06/zr1 cals do with this parameter.

 

[engineermike]

The gt500 has it set to 4096 deg but there could be some other means to control it. It’s a different os that I’m not as familiar with. The 2021+ Whipple f150 lowered it 100 deg to 1650, and 2024+ mustang doesn’t have the parameter at all, again, probably just controlled differently.

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