My check engine light came on last night while driving on the highway. I had a loud backfire while accelerating, then the car ran like crap. After I shut off, and checked everything, it started up and the idle was a bit off, and stumbling.

Car: 2005 Cavalier, Ecotec, Automatic


When I got home I put a scanner one it, and it came up with two P420 codes (catalyst system efficiency below threshold). The code scanner is a INNOVA scanner and has the OBD monitor. Its also showing these below have failed:

EV - Evaporative System Monitor
O - Oxygen Sensor Monitor
C - Catalyst Monitor
OH - Oxygen Sensor Monitor


I have a pacesetter header, downpipe, Magnaflow 91036 cat, 30 inch resonator, 2.5 pipe, Magnaflow muffler. The front O2 sensor is new (10,000 miles ago). My exhaust it a lot louder than before, and when I start it up is smells like its running rich... But goes away after 5 minutes. I also have a significant loss of power all the way to 65mph at WOT (haven't gone over 65 ph yet). My gas mileage has also gone way down, I used about 1/2 of a tank to drive 100 miles (most of it on the highway). About a week ago, installed new spark plugs (iridium A/C Delco) and the spark plug spring inserts from Greg B (jersey devil).

Any ideas on where I should start?

New car upgrade :

seriously, i would start by the cat....with all those codes i think the cat is bad, and if the cat isnt doing its job, the rear sensor will go bizerck......

the cat breaks down thr EXTRA gas that is not burned and turns it into "safe" gases for the car to emit. if it is not doing its job, then the exhaust coming from ur car is almost straight "vaporized" gas, which would cause the rich smell. and all this in turn would cause all the codes, and cause the sensors to go crazy, and casue the computer to try to adjsut for everything, which would cause all ur issues......CAT IT IS!!!!




Edited 2 time(s). Last edited Friday, October 03, 2008 2:44 PM

Well mabye you should spray the throttle body out with carb cleaner.. and tighten your front 02 censor and look at your rear and decide that its too much of a pain to get at.. then tap on your cat and resonator until your ears hurt.. and have a couple cigarettes with me until we take off your evap lines and put them back on (not doing anything to them.. just taking them off and putting them back on again) Then take it for a test drive and really give it some gas.. OH then stop in a puddle and do a burn out (X2 for effect).. mabye that will help.. OH WAIT! we did that.. and it DID WORK!

Good job us..

lol is all i can say to that