hey guys i am new to this site and i just got me got my lancer oz rally last week . the car came with 135000 miles on it and all the changes i did so far are
1.new spark plugs
2.new brakes pad and rotors
3.drained oil and changed the filter
4.power steering flush
5.new battery

but today i went to auto zone because the check engine light came on with P0421 Warm Up Catalytic Converter Efficiency Below Threshold and since then the car has been acting strange as its misfiring . Any ideas on wether i have to change the coil , cat converter or o2 sensors .

 

mods on the car?

 

no mods at all car is fully stock

 

i have tht exact same code come up on mine p0421 with 75kmiles 03 oz... i think tht code refers to the o2 sensor off the header.. mine has been like tht since april and i have no issues driving or starting up engine. the lancer drove fine to cypress, ca from san diego and back for mod 11....

have u check the plug wires/coil packs? the price of the first o2 , the one that sits on the header, sensor is under $20 last i check.. id replace the first o2 sensor first.. if the second o2 is bad, tht one sits on the cat itself and is more exp, tht one is around 300 last i check at autozone.

i havent bothered to replace the sensor on mine since i passed smogg in feb of this year...

 

I had the problem on mine. Its an 02 sensor problem or in my case a problem with factory relay that I had them do the recall on. Funny, it had 108k miles and they did the recall on it. anywho, I put an o2 fouler on the rear one and it fixed it for me.

 

thanx do you know where i can find the o2 sensor for less than 20$

 

also guys today i found out my alternator is bad keeps making my battery smelling like rotting eggs so i think i will buy this one and have my brother put it in http://cgi.ebay.com/ebaymotors/NEW-A...ht_2128wt_1103

 

check pepboys,autozone etc for the o2.. the first one is cheap .. but like juan said get the o2 fouler and see if it fixes it for you

 

ok will do this tomorrow early in the morning and i will let you know how it goes

 

i got the same thing but i replaced the 02 sensor on the mani,still there so im going to replace the downstream one and see what happens. oh if you know where to get an 02 sensor for less than $20 LET US KNOW cause their goin for $55-$90 lol but for that price not sure if id trust it.

 

Hey guys it was the spark plugs that were bad i changed them with the coils and the car has been running smooth now thnx for the help