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hey guys i have a question about everybodys check engine light coming on when they put a header and downpipe on does that hurt the engine and what does it mean why does it come on all i know is it has to do with the 02 sensors thanks for the help

 
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it puts the car into some kind of "safe mode" so its not getting all the right settings that the ECU normally uses when the light is off. I would imagine you are losing power with the CEL on because its limiting factors like fuel delivery, etc.

 
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and my other question guys is there anyway to prevent the cel from coming on once you install a downpipe w/ free flow cat like any type of different 02 sensors or anything i dont want an 02 sim by the way

 
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why dont you want an o2 simulator

 
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o2 sim is the only way.

 
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I have the HP Race w/hi flo cat. I got a CEL 2 trips after install and reset ECU, got another CEL 2 trips after reset. Reset again and it didn't come back.
THERE IS NO NEED FOR AN o2 SIM!!!

Pull the F.I/ECU fuse in your engine bay when you get the CEL 2 or 3 times and it wont come back. It is a learning computer, there is no need to trick it with an o2 sim.
If you dont want to reset the ECU go ahead and pay 50+ for the sim.
Good Luck.

 
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you dont even have to reset the ECU just drive around for a day or 2 and it will turn off.

 
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...and everythnig will be back to normal and no more fuel limiter, etc?

 
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I trip the CEL about twice a week b/c of my turbo (always for an emissions code) and after about 25 minutes it turns off.

 
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if you go into "limp mode" then urn the key on and off real quick.

 
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mine turns on after like 50 or so miles after i reset it, im told that you can use an o2 sensor for the front in the back to override the CEL... i will let you know in a few days

 
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ok.. putting an o2 sensor from the front in the rear doesnt help any... GRRRR

 
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Have you tried the MIL eliminator?

 
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^^ whats that?

 
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http://www.7thgencivic.com/forums/sh...hreadid=111201

http://www.bigjoshracing.com/store/shop/index.html

 
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When it threw the CEL for the hiflo cat, it didn't put the ecu into limp mode, I still had regular fuel maps. Full potential..im not positive but i think it only puts the car in limp mode for certain codes...depends on what your problem is. It WILL go away..

 
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well.. my cat is a straight through design.. at least i think it is... cause i can see through the entire pipe, it keeps throwing a code i dont know what the problem is.. i guess ill drive it around for a while and see, but my friend and i are working on an o2 simulator, but we kind of are stuck on the wiring diagrams.. would someone like to point me out to the ecu wireing diagram so i can figure out the RIGHT wires to splice into?

 
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Yes you have a hiflo cat, there is no catalyst's (honeycomb) inside the pipe. I would just reset the ECU a few times. It will eventually go away.