Tune question - failsafe cooling mode to keep cats cool?

[robertwsimpson]

Guys,

I have this issue where if I accelerate (not wide open, but maybe 50% throttle) to about 3k RPM, and then push the clutch and let off of the accelerator, the RPMs fall to about 2250 and level off for about a second and a half before falling the rest of the way to idle. I can make it do this pretty much every time I try. This in and of itself is not that bad, but I can feel it doing this when I'm in gear as well... when I let off of the pedal, I don't get the engine braking I'm expecting.

Tuner is telling me that this is part of the factory settings to protect the cats. I don't understand this. Does E85 run hotter than 91 octane?

mods are JLT intake, Borla cat back, Bama flexfuel tune

Please don't come here doing the normal bama trash talking. If you have valid information, I'd appreciate the input!

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[Nerass]

think its like a rev-match thing to make it easier to shift into the next gear idk

 

[Jay-rod427]

Clutch in rev hang is normal to make engaging the next gear easier. The non engine braking is because it doesn't go into defco(decel fuel cutoff) for a couple seconds after clutching. IMO has nothing to do with cat protection. Cat protection only applies when you've been on it hard and the cats get hot it will dump extra fuel to cool them back off.

 

[robertwsimpson]

hm interesting. Whatever it is, I do not like it at all.

 

[Kahboom]

Rev hang is a pita at times with Manual cars. It's annoying that's for sure. It would be nice to have it completely removed in a tune.

 

[arghx7]

Some of it is to reduce deceleration shock. Slam the throttle shut on an old throttle cable car and you can feel the chassis move. On electronic throttle they dampen and filter the pedal torque request signal as you tip in and tip out.

The other part is emissions related. It keeps too much unburned fuel from passing through (depends on fuel shut off pattern) or too much oxygen getting into the cat causing high NOX.

 

[robertwsimpson]

he said that if I do a cat delete, they tune it out completely.

 

[Kahboom]

Who is your tuner

 

[robertwsimpson]

Who is your tuner

Luis

 

[wildcatgoal]

I don't see how that has anything to do with the cats...

 

[robertwsimpson]

I don't see how that has anything to do with the cats...

He's saying that the engine pushes air and fuel through to cool the cats... He said that's in the stock tune and they don't mess with it unless you take the cats off.

I kind of get it, but also kind of not.:frusty:

 

[dev1360]

He's making stuff up, or you're interpreting it wrong.

The rev hang issue is simply the car hanging to help with shifting into the next gear. It is as simple as a button to turn it off in HPTuners (assuming your tuner is using HPT).

COT (Cat Over-Temp) is the car richening the mixture at WOT after a certain threshold to help cool the cats. COT is not active any other time than at WOT after a set amount of time or inferred cat temp. It just gives extra fuel to cool them.

 

[robertwsimpson]

ah thank you for your explanation. I was wondering how burning more would cool things down. Richening the mixture, I understand how that would be cooler than leaning it out.

I live fairly close to AED. I hear they are very good... after a few more go fast parts, I think I'll run out there to see what they have to say.

 

[arghx7]

ah thank you for your explanation. I was wondering how burning more would cool things down. Richening the mixture, I understand how that would be cooler than leaning it out.

I live fairly close to AED. I hear they are very good... after a few more go fast parts, I think I'll run out there to see what they have to say.

It's complicated.

The cat can heat up from going WOT, even though it's rich. If the fuel is cut on tip out of the accelerator pedal, and a lot of oxygen flows through the cat, it can cool the cat down. However, when you tip back in, the catalyst may not be able to process the NOx emission. There's a model inside the PCM to calculate how much oxygen is in the catalyst. Too much oxygen is bad for NOx emissions, too little oxygen is bad for HC and CO emission.

If the engine is under heavy load but not in power enrichment (stoichiometric air fuel ratio), the scavenging effect of the valve timing and manifolds can push extra oxygen in the catalyst, which heats it up.

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