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I don't have 7th gen, but a 99 Civic with the 1.6 Vtec. I just recently got the Ignition coil replaced, changed the fuel filter,and installed new spark plugs. Ever since this maintenence the check engine light has come on as well as the exhaust tone has changed. By the exhaust change i mean from a loudass shake the car tone to not loud at all. I took my car to autozone for the code to the check engine light and it threw a PO420. The reason for the changing of the coil and plugs: is running the car untill the plugs lost resistance and caused the coil to quit. Not my fault but the previous owner.With this code thrown, I took off the intake hoping to solve the problem. It keeps coming back on. My exhuast is just stock with a highflow rear muffler without the mid cat(resonator)(sp). Whatever the deal,changing the plugs and coil caused my car to come from 32MPG to 43MPG a HUGE improvement. However the check engine light is on, and I lost the exhaust tone that I loved. Any suggestions?

 
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i would go to autozone or somewhere and they check ur CEL code for free. See what it is and go from there.

 
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If you read the topic, you will see that I did that. It threw a PO420 code.

 
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P0420 = Catalyst System Efficiency Below Threshold

Maybe it is time for a new cat

http://www.troublecodes.net/honda/

 
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Hmmm. I wonder if that can be the cause of the exhaust tone? I hate to buy a new cat and that's not the problem.

 
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I believe emissions system warranties are the longest lasting for any vehicle, the stealership should replace a faulty catalytic converter for free.

 
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I've already gutted the cat..That solved the problem..