Mitsubishi Repair: 1998 Mitsubishi Mirage, clogged catalytic converter, mitsubishi mirage

Question
QUESTION: I have a 4 door, 4 cylinder, automatic, 1.4 liter 1998 Mitsubishi mirage. I have not had any problems with it until just recently. My alternator went bad. we fixed that and have had nothing but more problems. both my dad and my brothers are mechanically inclined and can not identify the problem. it has had a full tune up the computer has been changed the timing belt has been changed and the car will not start. My brother got it to run but it had no power and shortly after it stopped running again. we have taken it to a mechanic and after some time looking at it he said that it has to do with the august system and that there is so much back pressure it wont start. that does not seem to be the problem after 4 hours of looking at it and we are baffled we can not even think of what to look at next do you have any suggestions?

ANSWER: Elizabeth,
It is possible that you have a clogged catalytic converter or other exhaust component.  An easy trick your mechanic can try is to remove the O2 sensor before the catalytic converter to easy the pressure on the system.  Else, he can pull and replace the cat converter entirely.  I recently had a friend that was in your exact situation.  He replaced what was thought to be a bad alternator, and later turned out to be a bad cat converter.  But because he delayed replacing the cat, the back pressure got so bad it blew the engine.  Have your mechanic try working on the exhaust to rule out a clogged exhaust.  The price of a new exhaust is a lot cheaper than a new engine.
Good luck!

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QUESTION: We ruled out the cat we took the whole exhaust system apart and blew air through it and there were no clogs so we are back to square one. A guy at the part store said that it could possibly be the fuel pump and the mechanic thinks it could be the cold start sensor. Might you have any other advice?

Answer
Elizabeth,
Checking the fuel pump is definitely worth doing.  If you have yet to replace the fuel filter, you should do that.  The fuel pump can be activated by simply applying a 12 volt source to it.  Your mechanic can hook up a pressure gauge to the fuel line to see if the pump is performing nominally.  Your mechanic can also check the "cold start sensor" (there are several sensors in play during a cold start) by simply bypassing those senors with specific resistors to mimic a warm engine.  Your mass air sensor holds a couple of those sensors, so your mechanic may have luck looking there.
Good luck!