Rep Power: 0

Hey all! I need some help with my car troubles. My 2003 Honda Civic Lx is misfiring (P0301, P0302, P0300) and I am trying to figure out why. I have recently replaced the fuel injectors, plugs, coils, cat converter, both o2 sensors and air/oil filters with a high mileage oil change. The car has 217K miles, but has run great for a long time other than recently. However, I have been getting the misfire codes for the past few days and today the car stalled 5 times (twice in traffic!). Upon inspection, the cat converter was noticably red (clogged?). Would the cat converter cause the stalls and misfire codes? No codes for o2 sensors or cat converter at this time.

 
Rep Power: 518

The cat is glowing because it is trying hard to burn all the raw fuel your misfiring cylinders are passing into it.
Cat can definitely be damaged by getting it that hot, and it doesn't even take a minute to ruin it.
Does not matter that it is new, it only takes a minute to ruin it.
This is a secondary problem.

Your issue of the misfiring cylinders appears to be the primary problem.

Got compression test results?
Got valve adjustment?
Recheck compression after valve adjustment?

 
Rep Power: 156

That's a lot of variables to throw at your car at one time. It seems like the fuel is getting into the engine since the cat is red hot. I would look at your plugs and coils and make sure you're getting a spark.

 
Rep Power: 0

****UPDATE****

Ok guys, I appreciate all the quick responses and I apologize for my delay in getting back about this issue. I finally figured out what was wrong with the car.

Apparently, my head gasket failed and was leaking between two cylinders (not a cheap fix). Since this problem was out of my skill set, I had to go to the shop to get the gasket replaced and the cylinders machined...

However, the root of my problem was most likely caused by my radiator. While in the shop, I explained my problem and requested a full inspection to just confirm everything (including all the things I had replaced such as coils, sparks, cat converter, O2 sensors, and fuel injectors). During the inspection, the mechanic noticed (and I saw this too) that my radiator had a crack (crap).

Sooooo....long story short, I had to replace my head gasket, radiator, get the cylinders machined...all this after I had also replaced the other parts. Whew....what a head ache.

But things are not done yet. Now I get P1456 and P1457 errors. I replaced the gas cap as that typically corrects the P1457 error (since this is what I got first). However, today my car through on its engine light again and spit out the two errors. I recently changed my oil and filter. I noticed a couple drips on the exhaust pipe not far from the front-center of the car. However, I thought nothing of it since I had driven through a small puddle of water.

Upon inspection this evening, I see there is still a small wet spot close to the front driver-side behind the oil. No leaks from the oil from what I can tell, but I have not yet lifted the car to fully check it out.

My question is, could the leak be related to the P1456 and P1457 errors? If so, is there anything I should check first to not waste time and money? I plan to inspect the wet area tomorrow.

 
Rep Power: 0

I have the exact same car and its not the cat! Yes you may have an old cat but it's either a head gasket or battery issue. I had the same misfires. I replaced my battery and payed for the head gasket work. I also replaced a few spark plugs, my car runs fine now.