P0300 misfire code / cylinders 1, 3, and 5
 

I finally discovered that the right bank on my engine is experiencing the p0300 code. I also checked the cats and found that the right cat is showing misfire. (There is a counter that shows how many misfires have occurred) I have had the car in at Infiniti and Nissan and neither of them could find the problem. Now that I discovered the misfires, with my $99.00 Harbor Freight OBDII reader, what is the solution? Anyone with any thoughts to remedy this problem?

Neither of them could find the problem? That makes me question their level of skills/knowledge.

Off the top of my head without searching (but definitely search for that code on here), I would consider new O2 sensors, spark plugs, vacuum leaks, you could have a bad cat as well.

How many miles are on the car?

100k miles, coil packs, plugs have been changed. Swapped out the MAF's and the misfires are still on bank 1, so the MAF's are good. I have Fast Intentions resonated HFC's that I installed 20K miles ago. Since it's on right bank, I would believe it be either the O2 sensor, probably downstream, or the cat. If I had a vacuum leak, wouldn't both bank's be misfiring? The reason that I'm thinking maybe the downstream O2 sensor is that I have already replaced the upstream sensor two years ago, for a code.

What is your afr reading for bank 1 and 2?
if the upper stream o2 (afr) is bad, and reads lean, it will lead to a misfire....

if you are experiencing random misfire all from the same bank i would say its more than likely your catalytic converter has come apart or its turned sideways causing backpressure to occur and in turn causing the misfire. you can easily check to see if you have a bad cat by hooking up and vacuum gauge to a vacuum port and checking engine manifold vacuum. if you have back pressure if would show on the gauge.

Thanks Sound and Crook, I'm going to check the cat today. I actually have a new front O2 sensor that I purchased when I changed one 4 years ago. I was going to replace both, but than only replaced the right bank, which is the one I'm now having issues with. Probably take a chance, since I already have the part and install it.

I R&R the bank 1, sensor 1 with a new Denso sensor and took the car for a spin. This is the same drive that I took yesterday after I swapped the MAF's. On that drive I had something like 10 misfires, today after the change out, no misfires on either bank. I'll continue to monitor the situation, but for now I believe that we have solved the problem, thanks!

Good deal (and for future user searches) a lot of these misfires can be cleared up on the cars by replacing the upstream afr sensors... (often confused as o2 sensors.)
I wish I had a clearer understanding of this before I spent a fortune at the dealership, and they STILL couldn't find my problem. I had to go buy the software, data log while driving, and figure out the problem myself.
Lesson is, when you have misfires always check your afr readings to make sure they are in spec. May save you a bundle.....

great to hear this resolved your issue OP!...now if only someone would do a DIY on replacing the Bank 2 upstream sensor....for the life of me I cant reach it lol