So my cat started rattling. I took to a buddy of mines muffler shop. I told him a shop emptied it out years ago so a straight pipe should work fine. Well someone messed with it but they didn't empty it out so there was the rattle. Well it doesn't like the straight pipe. I tried disconnecting the battery hoping it would relearn, it tries to run good but then it will ping on and off and eventually throw a check engine light. It always says cylinder 5 misfire. Why just 5 I don't know. Since Cats are ridiculously expensive right now is there a chip or some kind of fooler to get around this? I have had it since new. Changed the intake around 5.2 throttle body cat back 3 inch exhaust, throttle body spacer, electric fan. Its always responded to changes fine. My ultimate goal is a Hemi swap but I've got a couple of cars in front of that project yet. Thoughts comments,

 

Lose the throttle body spacer, it isn't doing you any good.

Need to find out why it is missing on number 5. The cat isn't going to have anything to do with that. Something else is going on.

 

Most ham-handed hacks that hollow out a converter just drop a pipe down the hole until it reaches the other end. They don't empty it completely. Magnaflow universal cats are around a hundred bucks at autozone. Might get it cheaper elsewhere.

On the miss, move the spark plug to a different cylinder, and the plug wire to still another cylinder. If the problem follow you know what the problem is, if it doesn't change the distributor cap. If that doesn't solve it, it's probably the fuel injector.

 

I thought of this but just thought it to be a strange coincidence that the cat had been rattling for quite a while before I had the chance to take it in. I didn't drive 15 minutes and it started to act up. The tune up has just under 10,000 miles on it. I've seen a couple of people mention an o2 defouler but I can't find anything on that with that name

 

https://www.google.com/search?q=o2+s...hrome&ie=UTF-8

 

The O2 "adapter" is a spark plug defouler, which spaces the O2 out of the exhaust stream but still lets a bit through. The theory is that less exhaust passing fools the sensor into thinking there's still a cat, but it really only worked for the earlier iterations. Whether it will work for you or not is hit or miss. To really eliminate it you need something like HP Tuners, to just turn the rear O2 sensor off. I keep mine turned off because 99 percent of the time the only failure the rear O2 reports is a rear O2 failure. If the cat goes bad you have other problems like low power or awful smells.

It'll be a coincidence that your #5 cylinder started acting up at the same time. If the cat was causing a problem you'd be seeing problems across all cylinders, not just one.