CEL question - Hyundai Performance Forums

uncgelantra · 02-05-2004, 09:06 PM

Okay I installed SS 4-2-1 headers and removed the cat a while ago. The CEL didn't come on until 3 days later and then I had an AEM CAI installed yesturday and the CEL went off. Now it's about a day later and the light is back on. I don't mind as long as it's not affecting performance, but what can be causing this? The installer removed the battery so that should have been enough time to reset the ECU right? thanks.

Kemper · 02-05-2004, 10:00 PM

To play it safe, you should really get some kind of cat installed on your car. The very small performance increase is not worth environmental damage and any fines/emission control problems (with your state, county, city, etc.) you may have. The CEL may be the least of your worries.

Disconnecting the battery would reset the ECU long enough for the CEL to blink off for while.

01IMPORTSHARK · 02-06-2004, 12:10 PM

yeah. prob cuz u have test pipe. and its making the 2nd O2 sensor, if you have one read a shitty reading. mine is doing that but i have cat and no 2nd 02 bung. im have CEL too and im finishing my catback this wknd so it should be fixed

turbulence · 02-11-2004, 05:38 PM

the cel i got after the header install was something like "slow response from 2nd o2 sensor"

elantrax · 02-11-2004, 08:30 PM

ya if your ecu is reading a funny signal from the o2 sensor where the cat is it would pull back the performance from the motor. mostly the front o2 sensor does that like it would say something maybe like running to rich or lean then the engine would compensate for that being most likely loss of hp and performance. id put the cat back on you aint gaining any hp out of it not being there and with todays new cars they learn to make cats the least thing to worry about when coming to hp and power tuning from the factory.

nyne · 02-11-2004, 10:25 PM

the 2nd o2 sensor is to measure the effiency of the catalytic converter.
the first o2 sensor, is used for air/fuel mixture.

there is obviously a performance gain for replacing your stock catalytic onverter with a test pipe.(very simple here, smaller diameter catacomb'd path, vs. a straight piece of pipe, nothing preventing free flow of exhaust gasses, matched to the catback. However there are enviormental and legal issues regarding the modification.

I have a 'test pipe' for now, and I am going to be replacing it with a 2.5" high flow cat, and adding an o2 bung after my catalytic converter make everything nice and legal