I have done a search and I know the code my car is throwing is a Random misfire (PO300), but before I get to my question here is a bit of background leading to it.

List of problems:

- Axle back flang rusts and blows off. I take muffler off since I ordered a new Cat-back. During this time (I still havn't received my cat-back) the car develops a random misfire code, but doesn't loose any power.

- I figure this problem is due to spark plug, and with over 145,000 km's on the car I change my spark plugs.

- After changing plugs (NGK R Platinum plugs bought from Nissan Dealer) I accidently plug in harness for cylinder 2 into cylinder 4. I put everything back together and get a knock combined with mis-fires and what not. My buddy and I pull everything apart and put it back together again. Same thing.

I got frustrated and drove it home (about two blocks away). I pull everything apart and check the color of the plugs. Figure out the problem and motor runs fine.



NOW, the problem is my car is producing a random mis-fire code again and struggles with power above 3000rpm. Massive power loss in all gears and the only code I'm getting is P0300. I am also hearing a rattling from my exhaust. Any suggestions?


I'm possibly thinking it's the cat on my left bank that got plugged due to the mass amounts of fuel dumped into it, and then maybe the exhaust back pressure into the left bank is high-enough to bring the exhaust back into the cylinders and not allow complete combustion. Could I be right? Or wrong?

I apologize for the lengthy post, but I need to figure this out.


****EDIT****
car is 100% stock

 

Anything? From anyone?

**update**
I also get some sort of a burning smell coming from the car when/if i give it. It's not plastic, no rotten egg (sulfur smell).

I also heard a hissing sound from one of the coil packs, but I pulled the plug and saw it was running rather lean (as oppose to rich which usually happens with malfunctioning coil packs).

 

Take it to the dealer. It sounds too serious to troubleshoot online.

 

Sounds like a big leak on your plenum (the hissing and lean problem).

 

That won't cause a burining smell...

 

I'm gonna be hollowing out my cats when my exhaust gets in. I will see if the problem persists after that. I'm starting to believe there is an issue with coil-packs, but I'm hoping otherwise. I will keep updating, thanks for the suggestions.

 

I would guess Ignition Coils.

If its a random misfire that would be my first guess...that and plugs (but you already changed the plugs)

A quick test is to pull an ignition coil from the plug and see if it changes the way it is running. Coil packs from the dealership are like $80 a piece. You might be able to find some in the marketplace.

 

Modern low cost price low quality reduced coil packs are getting close to being just like spark plugs or plug wires............replace them as a package. Especially after 100k.

 

Thanks for the advice guys! So far I have done the ignition coil test. However, this really brought no luck. The engine reacted how it should after each coil was unplugged. Being a random misfire code, I could only assume that it happens just as described, random. I've only ever gotten the flashing CEL when the car was under heavy throttle load.

I have my exhaust, just waiting for my test pipes to come in so I can rid some of my assumptions.

 

I've never heard of cats being clogged and causing back pressure enough to throw a code...

 

**UPDATE**

for those who might have a similar issue, it was indeed my catalytic converters. They were actually clogged to a point where there was no flow coming out of the left bank. I could have only imagined that the cat's were on their way out already and this last event just killed it.

I am now currently running test pipes (temporarily) until my HFC's come in. I have all power back, and the car is not throwing any more mis-fire codes.

 

I had very simluar problem with wise-1. My friend changed my spark pluggs and got the P0300 (multiple misfire) code. Thinking the coils were bad, I've replaced the coils but still was causing the problem. I ended up taking it to the dealers and found out my friend mixed the coil wires. After that, everything was back to normal, so I've thought. Now I don't have check engine light on, but I have another problem. My exhaust sounds different (sounds very heavy, like something is clogged), sounds like vibrating and/or has a hole somewhere in the exhaust. When I place my hands on the exhaust, air flow seems even, don't know what's the problem. Also, I have massive power loss. Currently I am trying to replace my exhaust and hoping the problem will go away, but I would like to ask if anybody have any clue what is causing this.

 

This has happened to other people too.

 

NikkiJS,

I suggest you try replacing your exhaust. This problem was highly irritating for me b/c I was never 100% sure if it was electrical/mechanical/exhaust related.

At first I thought coils, but I swapped them out with a good set and drove around. Still same problem. As I awaited my exhaust's delivery, I just drove around with a choked up exhaust and no accelaration. Definately dis-heartening, especially since everyone knows our cars definately put out some decent power.

Anyways, I hope people who have similar issues find this thread.


**ALSO LISTEN FOR CORE RATTLING FROM CATALYTIC CONVERTERS!**

 

your "test" to feel the pressure out of the back is not valid since the exhaust is a single midpipe to dual mufflers so there is no relevance between the pressure from either exhaust tip and the cats since both cats are combined into 1 midpipe then split to 2 tips..