Cat questions

[bottomline2000]

Moving your front 02 sensors downstream only delays how long it takes the computer to read the exhaust flow. I don't think you want to move them further downstream, kinda like moving a wideband sensor further downstream. I can see the delay in my wideband and it's reading of the exhaust flow and it's just past my downstream O2s which are tuned out.

If the cats haven't failed u are probably better off keeping them. I've heard even stock cats are high flow..

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[kbuskill]

I emailed Lew, from Diablew, which is who did my custom tune...

Here is my email to him...

"Hey Lew,

I have a couple quick questions for you.
You had mentioned down stream O2 codes and it got me to thinking.

Q1. Can you turn off the down stream O2 sensors on my 2008 Suburban?

Q2. If I hollowed out the cats and disabled the rear O2 sensors would there be any benefits/gains in power or torque?

Q3. If we did disable the rear O2 sensors because I hollowed out the cats.... Would it make sense to move the up stream O2 sensors back to the downstream O2 sensors location in the pipes by using wire extensions?

These are just some thoughts that I have been running through my head and since you are the tuning guru I figured I would ask you to get some better understanding.

Thanks for your time, Ken"

And his response to me...

1 - yes the rear o2 codes can be disabled if you remove cats, add headers, etc..

2 - no benefits... wouldn't gain you much of anything.. you will have more raw fuel smell...

3 - And noooooo!!! you can't do that man.. the front o2 sensors HAVE to stay in the front where they are! those are the important ones, those control the fueling/fuel trims.. the front o2 sensors have to be installed where they are, in the front.. you can not remove them or put them in the rear.
Thanks!
-- Lew
-- a.k.a. DiabLew / 06MonteSS
-- www.diablewtune.com

I don't think he quite understood what I was meaning about moving the O2 sensors back.

I can understand it being an issue if the cats weren't removed, but with the cats out of the way I don't see where it would be any different other than them being further from the heads and therefore it might possibly read cooler numbers than normal.

 

[kbuskill]

Moving your front 02 sensors downstream only delays how long it takes the computer to read the exhaust flow. I don't think you want to move them further downstream, kinda like moving a wideband sensor further downstream. I can see the delay in my wideband and it's reading of the exhaust flow and it's just past my downstream O2s which are tuned out.

If the cats haven't failed u are probably better off keeping them. I've heard even stock cats are high flow..

Sent from my SAMSUNG-SM-T377A using Tapatalk

That makes sense... like I said... just a dumb idea I had... lol

So since you have your downstream O2 sensors tuned out...

Can you still see your "cat" temperatures on a scanner like torque pro???

I was under the assumption that the cat temperature was gathered from the downstream sensors (after the cats) BUT when I look at the title of those sensors on torque pro it say "Bank 1 sensor 1" and "Bank 2 sensor 1" so that leads me to believe that the temperature is actually pre cat temps.

 

[swathdiver]

Without those downstream O2 sensors or something to replace them, I reckon his computer does not see them anymore.

I have no recollection of our cars being smelly or raw fuel smell running without cats. Now we can even tune for it. Is everyone afraid to say to do it these days? LOL Besides, if you're running FlexFuel, is not going to smell of gasoline anyways!

I like the idea of the small tube shorties, everything to make torque down where we drive is good to me.

1. Baseline the truck for three passes.
2. Install Shorties and make three more runs.
3. If you gut the cats, make three more runs.
4. If you have done #3, then move the O2 sensors and make 3 more runs.

I've been looking at Banks' iDash 1.8, two of them on a pillar pod would provide a mountain of information while driving.

 

[kbuskill]

Without those downstream O2 sensors or something to replace them, I reckon his computer does not see them anymore.

I have no recollection of our cars being smelly or raw fuel smell running without cats. Now we can even tune for it. Is everyone afraid to say to do it these days? LOL Besides, if you're running FlexFuel, is not going to smell of gasoline anyways!

I like the idea of the small tube shorties, everything to make torque down where we drive is good to me.

1. Baseline the truck for three passes.
2. Install Shorties and make three more runs.
3. If you gut the cats, make three more runs.
4. If you have done #3, then move the O2 sensors and make 3 more runs.

I've been looking at Banks' iDash 1.8, two of them on a pillar pod would provide a mountain of information while driving.

My plan is similar to what you stated..

1. Baseline the truck for three passes.
2. Install Shorties and make three more runs.
3. Remove the cats and make 3 more runs.
4. Have the truck returned with rear O2 sensors tuned out and make 3 more runs.

Gonna see if Lew can send me an updated tune with the rear cats deleted so I don't have to stare at a CEL while I am logging to get the new updated tune.

I am still trying to figure out the logging on the Torque Pro app.

I set the graphing up earlier to record HP, TQ, KR, and ethanol content but then closed the app and when I went back into it the stuff hadn't saved... I guess you have to set it up every time.

Can you think of any other sensors that would be good to graph, from a performance stand point, while making those runs???

I was also thinking of just finding an app to record this screen...


while making those runs.

 

[swathdiver]

My plan is similar to what you stated..

1. Baseline the truck for three passes.
2. Install Shorties and make three more runs.
3. Remove the cats and make 3 more runs.
4. Have the truck returned with rear O2 sensors tuned out and make 3 more runs.

Gonna see if Lew can send me an updated tune with the rear cats deleted so I don't have to stare at a CEL while I am logging to get the new updated tune.

I am still trying to figure out the logging on the Torque Pro app.

I set the graphing up earlier to record HP, TQ, KR, and ethanol content but then closed the app and when I went back into it the stuff hadn't saved... I guess you have to set it up every time.

Can you think of any other sensors that would be good to graph, from a performance stand point, while making those runs???

I was also thinking of just finding an app to record this screen...
View attachment 214516

while making those runs.

Looks good but too much to look at while racing err logging!, so you'll want to record and watch it later. You're just making three runs and not changing anything between them other than the mods. Are the cat temps serving as a poor man's EGT gauge?

Oh, can it calculate MPH at the end of the 1/8 and 1/4 mile? How about distance to 60 mph and 60 foot times? Those are muy importante!

 

[kbuskill]

Looks good but too much to look at while racing err logging!, so you'll want to record and watch it later. You're just making three runs and not changing anything between them other than the mods. Are the cat temps serving as a poor man's EGT gauge?

Oh, can it calculate MPH at the end of the 1/8 and 1/4 mile? How about distance to 60 mph and 60 foot times? Those are muy importante!

Yes on the poor man's EGT gauge... lol

That was actually one of my questions... if I have the rear O2 sensors turned off will the "cat" temps still read?

What I mean is, do those readings come from the front or rear O2 sensors???

Yes I believe it tells you at the bottom of the 1/8-1/4 mile gauges what your speed was but I can't remember for sure... not something I play with every day. I know it shows you how long it takes for sure.

It does 0-60mph times... not sure about distance or 60ft times.

 

[swathdiver]

Yes on the poor man's EGT gauge... lol

That was actually one of my questions... if I have the rear O2 sensors turned off will the "cat" temps still read?

What I mean is, do those readings come from the front or rear O2 sensors???

Yes I believe it tells you at the bottom of the 1/8-1/4 mile gauges what your speed was but I can't remember for sure... not something I play with every day. I know it shows you how long it takes for sure.

It does 0-60mph times... not sure about distance or 60ft times.

I think so Ken. They are calculated and not actual too.

 

[bottomline2000]

That makes sense... like I said... just a dumb idea I had... lol

So since you have your downstream O2 sensors tuned out...
9i
Can you still see your "cat" temperatures on a scanner like torque pro???

I was under the assumption that the cat temperature was gathered from the downstream sensors (after the cats) BUT when I look at the title of those sensors on torque pro it say "Bank 1 sensor 1" and "Bank 2 sensor 1" so that leads me to believe that the temperature is actually pre cat temps.

I have an Autocal and my truck is Efi Live tuned. I'm going to check some datalogs tomorrow and confirm but I don't think my rear cats still show in the log. My EGR is also tuned out, but my wideband is now connected to that port to datalog A/F ratios. Justin must be able to see the EGR port since he adjusted my tune after a log and it's right at 12.5 at WOT..

One thing I think is helpful us I can see my longterm/short term fuel trims and that will give me an idea if my cats are acting up too if either bank has a big deviation from 0.

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[LanceD]

I deleted my cats. Sounds better and seems to have a little more power.