removing the two catalysts converters under the JK
09-19-2009, 05:09 PM
#11
JK Jedi Master
From what I see it looks like the second two are just resonators. The first o2 sensors(before the cats) dictate A/F ratio. The second o2 sensors(after cats) just monitor emissions.
So putting test pipes in way of the resonators won't be a problem at all. I'd want to hear the sound though. Resonators often take the raspiness out of exhaust notes. I've had friends take resonators out of stock exhausts before and it's sounded like ass.
To jump on what Redneck was saying about actually replacing the cats with test pipes is easier said then done. A o2 simulator could easily be used on the "after cat sensors" to "trick" the OBDII system into thinking the cats are still there.
My question would to worry about how much removing the cats would "lean" out the A/F when in Open Loop.
However, the downstream O2 sensors don't simply monitor emmissions. They keep track of how much O2 makes it through the catalyst as a way of tracking the age/effectiveness of the catalyst, based on the fact that when a catalyst ages, it loses some of its oxygen storage capacity.
In your last sentence, did you mean closed loop? Open Loop is before things warm up. Closed Loop is when everything is functioning, and the computer is using info from all the sensors. It is then a closed system.
09-19-2009, 05:24 PM
#13
It is true the upstream O2 sensors feed data to the computer for air/fuel ratio.
However, the downstream O2 sensors don't simply monitor emissions. They keep track of how much O2 makes it through the catalyst as a way of tracking the age/effectiveness of the catalyst, based on the fact that when a catalyst ages, it loses some of its oxygen storage capacity.
However, the downstream O2 sensors don't simply monitor emissions. They keep track of how much O2 makes it through the catalyst as a way of tracking the age/effectiveness of the catalyst, based on the fact that when a catalyst ages, it loses some of its oxygen storage capacity.
At Closed Loop the ECU will tune the A/F to 14.7 or stoich. Modifying exhaust componets don't really effect Closed Loop performance since the ECU will compensate.
Last edited by drumnatural; 09-19-2009 at 05:27 PM.
09-19-2009, 05:28 PM
#14
JK Jedi Master
Never heard that before. Regardless they can be tricked electronically or mechanically to make them think the catalyst is still there/working.
It's Open Loop I'm concerned with. In an OBDII system Open Loop is pre-determined by the ECU to add "x" amount of fuel. Open Loop occurs when you give it a certain amount of throttle. Closed Loop is when your giving it part throttle. The ECU will switch from Closed Loop to Open Loop based on throttle position.
It's Open Loop I'm concerned with. In an OBDII system Open Loop is pre-determined by the ECU to add "x" amount of fuel. Open Loop occurs when you give it a certain amount of throttle. Closed Loop is when your giving it part throttle. The ECU will switch from Closed Loop to Open Loop based on throttle position.
09-19-2009, 05:39 PM
#15
Thats not always a bad thing though. Most ECU's run the motors very "rich" from the factory.
You will actually gain power from leaning out. But there is a balance. Run too lean and the motor goes BOOM
Most vehicles can have long tube headers, no cats, and a larger diameter exhaust and not run dangerously lean though.
But I don't know how finicky the JK's are.
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Jeepjirau (12-25-2023)
09-19-2009, 05:49 PM
#16
JK Jedi Master
Kind of. If you open up an exhaust system it will "lean" out the Open Loop map.
Thats not always a bad thing though. Most ECU's run the motors very "rich" from the factory.
You will actually gain power from leaning out. But there is a balance. Run too lean and the motor goes BOOM
Most vehicles can have long tube headers, no cats, and a larger diameter exhaust and not run dangerously lean though.
But I don't know how finicky the JK's are.
Thats not always a bad thing though. Most ECU's run the motors very "rich" from the factory.
You will actually gain power from leaning out. But there is a balance. Run too lean and the motor goes BOOM
Most vehicles can have long tube headers, no cats, and a larger diameter exhaust and not run dangerously lean though.
But I don't know how finicky the JK's are.
09-19-2009, 05:56 PM
#17
So in Closed Loop the ECU will try to keep the A/F ratio around 14.7
What we need are dyno graphs with the A/F ratios taken.
I was just thinking on removing them in order to have a better sound. 
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Jeepjirau (12-25-2023)
04-14-2011, 05:33 PM
#19
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Is it true that as far as performance the A/F ratio would be 12.5 (something around there), I say that cause in tuning GSXR 1000's we seen 12.5or 12.7 to be great performance????? just askin where the best performance for a gas motor is, roughly.
