i just installed my Magen race header on my eclipse gs and it's acting strange. it's a little jumpy/hopping and the engine light came out. any clue of what it is'?

Take your car to auto zone and get the code checked and then report back.

Make sure you have everything nice and tight; sounds like you have an exhaust leak. Listen for hisses, if that doesn’t work put it on the scanner...

Did you screw your O2 back in and block off the extra port?

MB

You could also do the keydance and find out what your CEL is. The exhaust leak one is something I'd look into as well. Check the seal for the gasket and make sure everything is bolted up well.

Also Mark's advice is great as well. On the headers with the cap-off on the opposite side of the header, make sure that's nice and tight and that your 02 sensor is tight as well. You might want to think about getting the cap just welded shut.

Good luck man and hope you get your problem fixed.

yeah we used an airgun to bolt everything back in idk how there could be a leak.... i'll check on the engine check light though. but it turns out i need new front drivers side motor mounts and the rear motor mount. thanx again

Question number 1) is it a 4-1 race header or a 4-2-1 race header?

2) Are you sure you put all the gaskets on and that there weren't any tears in them?

3) If it is a 4-2-1 design, does he middle section connect with a gasket or does one side slip over the other?

4) Front O2 sensor placed back in the new header?

Anyways the popping is normal, especially when coming down the gears from higher speeds. When you place your hand near all of the connections/gaskets of the header do you feel any air?

CEL light feels like an O2 sensor problem to me, did you make any other changes to the car during this install?

Anyways if you can answer all of these questions, then you should be good. And the CEL Should be a different problem.

Lastly, Air tools are usually good, but when you run into a problem like this, its a good idea to torque everything by hand at the end of a job.

I'm with mark and randy here. Front o2 sensor.

^ +1