so i have had this problem for over a year now and no mechanic has been able to find the problem. my car is misfiring all 4 cylinders. p0300 p0301 p0302 p0303 p0304. this all started happening after i changed my catalytic converter after having p0420. it was replaced with an aftermarket magnaflow cat, along with it i got the exhaust done with a magnaflow muffler and custom piping and secondary cat delete. will this cause the misfires? i just talked to 2 of my buddies that build race trucks and they said theyre positive thats the problem. just looking for some feedback on that.

they said that the secondary cat delete was not making enough backpressure

 

secondary cat shouldn't cause misfires. Plenty of ppl around with 2nd cat delete (aka catback exhausts). May have something to do with the primary you replaced. It might be messing up the flow (or wasn't installed properly). Run a set of catless headers or swap manifolds with someone to see if the problem still persists.

 

Yeah, that primary cat that you had replaced is smoked. You were exactly right about the back pressure but it's about the primary catalytic converter. It will not allow exhaust gas to exit properly, once the gas pressure builds up, it will be pushed back into to the combustion chamber and re-mix with the clean air. This will not allow the clean air and fuel mixture to ignite properly causing misfires. Get that sucker replaced with something else like Justin said. Let us know.

 

thanks guys. now i feel more confident about dropping some more money on trying to get this fixed. i've had this problem for a year now and no mechanic was able to find the problem. i changed ignition coils, spark plugs, and checked everything that can possibly cause a misfire and nothing. im gonna order the stock manifold/cat, down pipe, and catback exhaust, have it installed and let you guys know how things go.