What is the benefit of decat?

[addertooth]

Some states (Like California) has stricter rules, but most states have the same basic rules. Some states carefully check the vehicles anually; some states do not check or enforce the rules unless you live in a major city (Like Arizona).

[antinym]

Florida doesn't check anything at all, ever.

[Gunpilot]

Alabama doesn't check anything either. You can drive a smoke generator here and they thank you for helping out the skeeter truck driver. I saw my neighbor throw his used motor oil away last week in used milk jugs but it's also legal to dump it in your yard.

[Secret Chimp]

Removing the catalytic converter decreases the backpressure in your exhaust system. In order to actually see any performance gain from removing your cat, you need to have your ecu retuned.

[irox]

Don't know if its the same; but when I re-cat'ed my Esprit to 200 cells, I did a hard reset on my ECU causing it to retune (relearn).

But Elige have MAF, not MAP sensors... That could be the controlling item

[Secret Chimp]

Originally Posted by spree

Don't know if its the same; but when I re-cat'ed my Esprit to 200 cells, I did a hard reset on my ECU causing it to retune (relearn).

But Elige have MAF, not MAP sensors... That could be the controlling item

I have no idea how a v8 Esprit works, unfortunately. I don't have a lot of experience with my Lotus Exige as of yet either...But I do have lots of experience with other cars.

When you remove the cat from most OBD-II compliant cars, a cel is often triggered because the oxygen sensor that sits post-cat in the exhaust is no longer happy. To be happy, the ecu wants to see a differential in the readings between the o2 sensor that sits pre-cat and the one that sits post-cat. That is how the ecu can tell that the cat is working. If it thinks the cat is not working, the ecu can/may/will do a few things.

1. It can throw a CEL. "Hey, I think something is broken. I should let the owner know."
2. It can start adjusting the a/f. "I'm seeing weird numbers. I should adjust the a/f till I see the readings I want."
3. It can stick itself into closed loop mode. "I don't have all the data I need to safely/properly adjust the a/f. As a result, I'm switching over to a map that I know will work until we get fixed."

All these things can lead to decreased performance and increase fuel usage.

So, what I'm getting at is, if you remove the cat and you do not have a way of tricking the ecu into thinking the cat is operating as it should (via adjustments to the ecu or an 02 sensor hack), you will often see no performance gain by removing your cats.

[creaturekris]

You will need something like this to go along with the cat delete to move the second sensor out of the exhaust stream.
O2 Simulator, angled, cel fix

[irox]

Originally Posted by Secret Chimp

I have no idea how a v8 Esprit works, unfortunately. I don't have a lot of experience with my Lotus Exige as of yet either...But I do have lots of experience with other cars.

When you remove the cat from most OBD-II compliant cars, a cel is often triggered because the oxygen sensor that sits post-cat in the exhaust is no longer happy. To be happy, the ecu wants to see a differential in the readings between the o2 sensor that sits pre-cat and the one that sits post-cat. That is how the ecu can tell that the cat is working. If it thinks the cat is not working, the ecu can/may/will do a few things.

1. It can throw a CEL. "Hey, I think something is broken. I should let the owner know."
2. It can start adjusting the a/f. "I'm seeing weird numbers. I should adjust the a/f till I see the readings I want."
3. It can stick itself into closed loop mode. "I don't have all the data I need to safely/properly adjust the a/f. As a result, I'm switching over to a map that I know will work until we get fixed."

All these things can lead to decreased performance and increase fuel usage.

So, what I'm getting at is, if you remove the cat and you do not have a way of tricking the ecu into thinking the cat is operating as it should (via adjustments to the ecu or an 02 sensor hack), you will often see no performance gain by removing your cats.

It's exactly as you described (excellent desc, BTW); except for the ECU tune part. The Esprit's ECU tunes itself (learns) after a hard reset. No external tuning avail, except by tricking the sensors as you recommend. I installed bung extensions as "insurance" even though I did not do a full de-cat; only dropped from ~600 to 200 cells which should have maintained an acceptable differential.

The part I'm not sure of is if decatting changes, increases, the air flow measured by the Elige MAF sensor; whereas the Esprit measures air pressure which remains the same.

[Formula1]

I just installed a 2bular decat with my 2bular GT3 muffler. I didn't reset the ECU. I felt a decease in low end torque. I have a mini-cat O2 bung solution that was suggested to me by 2bular and it works great (no CEL). The question is should I reset the ECU? Will that help the low end torque loss or is that due to the lack of back pressure inherent to a free'r flowing exhaust?

Btw, I have a 2011 Exige RGB with the S260 factory tune.

Thanks!
John

[Secret Chimp]

Yes, you should reset the ecu. It's usually good practice to reset after each mod.

If nothing else, it's a free and easy way to help diagnose your issue. If resetting the ecu doesn't help, the decreased torque might be normal (I doubt it though since you are supercharged) or it might be due to some other issue you created when putting in the new exhaust (air leaks in exhaust prior to o2 sensors).

[Formula1]

I'll go ahead and reset it. Honestly, I may revert back to a cat. Since I don't plan on heavily modding my car, I just don't know if it's really worth the negative environmental impact. If so, I'll be selling the decat with the mini cat. It's been on the car for ~500 miles, basically brand new!

Thanks!

[Saketome]

How do you reset your ecu?


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[Formula1]

Originally Posted by Saketome

How do you reset your ecu?


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I assume its as simple as disconnecting the battery. Correct me if I'm wrong!


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[irox]

Don't know about the Elise/Exige; the Esprit OBD command set supports an ECU reset... I forget the hex values... But would probably be different anyway. A battery disconnect might do it...

[Saketome]

Originally Posted by Formula1

I assume its as simple as disconnecting the battery. Correct me if I'm wrong!


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Im just wondering... How come when I disconnect and reconnect the battery the odometer trip meter reading is still the same and the radio channel and setup don't change. Unlike my other cars the trip meter goes to zero and radio channels and setup changes.


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[Saketome]

Anybody?...


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[EricH]

This conversation is drifting from the thread title but -
My radio always resets.. both the time and all the stations. I've never looked at the trip odo. My Exige came factory with an Alpine CDE-9872.

[shay2nak]

you need the Lotus Scan3 tool to actually reset the ECU. go to the dealer.

[Saketome]

Originally Posted by EricH

This conversation is drifting from the thread title but -
My radio always resets.. both the time and all the stations. I've never looked at the trip odo. My Exige came factory with an Alpine CDE-9872.

Sorry for the off topic.. My elise came with a blaupunkt.

Originally Posted by shay2nak

you need the Lotus Scan3 tool to actually reset the ECU. go to the dealer.

I see, thanks.


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[Drew09]

this:

FLAME THROWER & Loud Revs: Lotus Elise with Arqray Euro Tip Exhaust - YouTube

FLAME THROWER & Loud Revs: Lotus Elise with Arqray Euro Tip Exhaust - YouTube