Subject: Passing smog
Question: Hi, I have a 90 Mitsu. Eclipse Gs, that Iam can't
get to pass, I have Done EGR,Cadlettic Cov. still
on the Smog it shows RICH- would the OXYgen sencer
need to be Changed.
Help. any ideas ???????
Thanks Mike
Answer: Mike,
Your oxygen sensor is definately a possibility for causing the smog sensor to get a RICH reading. When the oxygen sensor fails, your car's computer can no longer sense the air/fuel ratio, so it ends up guessing. Your car performs poorly and uses more fuel than it needs to.

Another possibility is that you have a dirty air filter. If you haven't changed your air filter in past 12k miles or so, this is a good time to do it.

If neither of those things helps you pass, you may want to have your ECU inspected (your car's computer). There is a problem with older Mitsubishi cars that is becoming more and more common. Very few people (including Mitsu mechanics) know of this issue. You can read about this problem here:
http://90gsx.com/eclipse/cap/caps.htm

Good luck!