i put my boy's used knock sensor in my car last week, and the misfire code went away.. so yesterday i throw in the brand new knock sensor just to have a new one in there.. got the computer scanned today, and the code came back!! WTF!!?? i'm about to go out in a few minutes and put the used one back in.. lol.. i just figured the new one would be stronger??? guess not... the car still feels strong though

 

i only have 77k on my car

 

I would still check the o2 sensor's, I have less miles on my car and one of mine went bad from running rich. I should have tuned the car sooner after I installed the headers and the o2 sensor would have been ok.

I had crappy gas mileage with rough idle plus the P0300 code and after I got the o2 sensor fixed, the code went away and has not come back, and car is running good...knock on wood...

 

interesting... so the P0300 code was the only code you had, and the O2 sensor fixed the problem?

 

Usually with this code it's probably your number 3 Coil or multiply miss fires. Try changing all 6 coils or the number 3 coil. If this doesn't work test your O2 sensors..........

 

thats pretty odd unless you happened to get a defective KS. I was thinking that you may have a bad valve cover, which would have oil leak into the spark plug chamber preventing the spark to fire the cylinder, but since the old sensor made the cel go away and brought your power back, i guess rule that one out.

 

i tried all that.. plugs, coils, vacuum pressure, knock sensor.. i guess the O2 sensors are next -sigh-

well, now that i put the used one back in there, i'm gonna take it back to get it scanned again in a couple days to see what comes up.. i replaced both valve covers with 04 valve covers.. however, there's still oil getting into the spark plug chamber.. but oil doesn't prevent the plug from firing anyway, so that wouldnt be it.. if that was the case then many many more 5.5 gens on this board would have the same problem.. lol

 

Well P0300 was not the only code I had. I had P1147 and P1167 also and once I fixed the o2 sensor and also added some resistors to my o2 simulator circuit then all the codes went away and have not come back. It has been almost 6-7 months since i have done that.

 

Did you replace all stuff at same time? If not it would be possible to rule out some. I suspect however, the P1147 and P1167 being secondary o2s could not cause the problem by themselves. How did you modify the sim?

 

Sorry I was confusing you with someone else from that nwp meet.

It was a combination of a bad sim at first, and then a wiring ****-up by the knuclehead that reinstalled the new sim

But when he was getting the 0300 and rough idle it was a primary o2. The cool thing about his car was that when I took it out I immediatly knew that it was the cause of the problem because it was rattling inside- clearly had a broken ceramic tip yet the ecu never ever came up with a code for that o2 sensor. I've seen them not rattle, not come up with codes, and still cause 0300's or 0420's enough times that I've lost count.

 

Good read. I have the same issue but it was right after the JWT cams went in (P 0300 code). And that was 4 years ago. I had 2 other performance shops look into it and nothing. Does yours check engine light blink if your sitting at a red light to long? When my car was out in C.A. the guy doing the turbo called JWT and told the story of my car, all the JWT said is my engine is bad. No help. Everyone told me its from the cams looping (mildly) and sending a code.

Can`t really help here but I`ll be watching to see if anyone can solve this problem.

 

Well good news, bad news. The good news is that my CEL (P0300) came on today while Kevin G. was looking at something else today and we discovered that the PCV hose had come loose so that was the reason the CEL P0300 code came on today.

The bad news is that the o2 sensor is 'probably' not the solution on fixing the dreaded P0300 code. Sorry about giving premature advice. I would recommend looking for vacuum leaks or checking the PCV hose...

 

All I can chime in about the O2 sensors + Misfire code, is that I had both at one point. I forgot the exact code, but it was for Bank 2 and this was solved by my ECM getting updated at the dealership. I had gotten a new AM600 MAF, then done the updated ECM program, and only the misfire code remained.

 

Its sounds like i have a vacuum leak around PCV valve area.. But everythings seems fine. Ive got a new PCV too

 

I have a 6th Gen and noticed my CEL came on with engine misfire after I installed headers and had it dyno tuned. I notice that the idle is a bit erratic and that there is a bit of a miss when I just barely crack open the throttle. I suspect lean idle. Can this be adjusted on a 6th Gen?

 

nice read...same code, replaced plugs with iridiums, bought coil packs(not grey dot), cleaned maf, was about to reporder grey dots this weekend but i think im gonna try the o2 instead.
rough high idle
not getting the power it should
thanks for the advice

 

I forgot to mention I replaced the spark plugs and cleaned Idle Valve too but still got the code.

 

interesting... i never thought about the O2 sensors.. now these would be the ones plugging directly into the headers right?

is there a way to test you O2 sensors to see if they're bad?

btw, i'm taking the car to autozone either tomorrow or wednesday to see if that P0300 code is gone now that the used knock sensor is back in there

 

If it is the o2's.. Would a o2 sim fix the issue?

 

ok, i got the computer scanned today, and the P0300 is still freakin there! WTF man... but the code said "pending..." what the hell does that mean?

 

Has anyone tried changing the fuel filter? I wonder if that could cause a misfire.

 

you gotta go inside the gas tank for that.. but gotdamn, at this point anythings worth a freakin shot man.. i'm at my wit's end...

 

Certain codes have a multi trip detection, basically they have to happen a certain amount of times before it wil trip the CEL & be considered a real code, but if it detects that code just once it will still store it as a pending code.

You can always perform a "boost leak test" to see if you have any vacuum leaks.

 

so it might not actually be a permanent code then? i'll get it scanned again soon.. i rented a tool from advance auto to do the vacuum test.. my vacuum pressure was 19 HG, at idle, which is considered normal

 

anyone wanna change the fuel filter and see what happens?

 

you know i just read over professor's thread about changing the fuel filter, and how that got rid of his P0300 code.. this is on my to-do list

i suspected something in the fuel system because for a while my gas tank wouldn't fill up all the way to the top.. like you know how the needle is supposed to go a little past the "F" line when it' full? well mine only went up to the F line for a while.. i was wondering what was going on, but didin't think it was a big issue

then one day i fill up my gas tank, and it filled all the way to the top... AND my SES light was gone it came back later that day, but i just thought that was very interesting.. so i'm gonna try this fuel filter thing and see if that helps

 

^^Good luck

 

mine just came on today - idle has been a bit rough, and my mpg has been between 24-25. checked for leaks; next step will be plugs. hopefully that will do the trick. hopefully i won't have to go through what some of you guys have!

 

When i first bought mine. It had the p0300. The dealer was about 200 miles from my house and about 20-30 miles into the drive it went away and didn't come back until i changed my plugs.

 

are your coils grey dot stk??

 

Anything new yet?

 

naa, nothing new.. i was gonna just buy a new coil and play around trying to figure out which one it is, but i'm taking it to my boy who works at a dealer and see what he can come up with

 

ok so i have the same problem with this stupid P0300. I put on the 02 sim this week and today the car started mis firing. soooo...im guessing if i take out the sim it will go back to normal??? I will try this tomorrow...damn, loss of HP isnt fun...

 

I just had the head gasket replaced on my 00 maxima with 217,000 miles. They also sent the heads to be machined. This had to be done twice because I guess they didn't do the heads right the first time and the car was super rough. They machined and adjusted the heads again and this time it was running smooth. But now I got the p0300 code all of a sudden. Whats going on?

 

UPDATE

Took the car to my boy who is a Nissan tech today. He scanned the computer, which said that there was a misfire in cylinder #2. The plug was good, so he threw a new coil in there, scanned it again, and the misfire code is now gone. However, I don't notice a difference in performance, and I still have a rough idle occasionally. Maybe the car needs time to adjust to the new coil??

 

May sound stupid but I was wondering how everyone was finding that they were pulling error codes from their ECU... Are they checking after their check engine light goes on or checking the actual ECU itself... The reason I ask is because I'm only getting around 286 miles to a tank which seems really low to me. I had a 90k done on the car a month or so ago even though the car has about 77k on it.. No plug replacement or coils...So I was wondering why such bad gas...How can I see if i'm throwing up errors on my ecu?

 

most people scan it after the SES light comes on.. i always took mine to autozone where they scan it and pull your codes for free.. how much were you getting to the tank before?

 

To all that are having this problem, which I am one of them! I talked to a mechanic friend of mine back in Chicago who has done a lot of work on Maxima's and run across this problem (not only in Max but other brands as well). I told me that there's a 90% chance it’s the CAT, which is clogged! 2 things you can do to test this, (1) Remove the CAT drive the car and get up to speed (just don't test at ideal), if it's the CAT, you should have your performance back and be a very load car. (2) If you don't feel comfortable with removing the CAT, start your car and let it run for a while (about 20 minutes or so). You should do this at night when its dark out, after the car has ran for a while, look underneath at the CAT and see if it is glowing. If it is, the CAT is the problem. He said that this only about 60% effective in testing this problem.

The problem is that CAT is clogged and creating back-pressure into the engine, because a lean-mixture, hence the P0300 code, no specific cylinder indicated in the misfire, all of them are misfiring. The fuel mixture has no place to go so it builds up and causes the poor performance, hesitation, sputtering and stalling. You might also be experiencing “intake back-fire”, that is because the fuel mixture only way to escape is out the way it came in.
I am going to test this out tonight when I get off from work and I will update. Please chime in if you try this and have success or failure. This is a complex problem and I know many of us are frustrated and want answers. This is what I was able to find.
GOOD LUCK!

 

Good stuff. This is probably my problem. I get the sputtering and it sounds like back pressure in the exhaust when I first start the car. After it runs awhile it goes away. I will try to see if the cat glows tonite.

 

Same here. I had a leaky seal around my 5th and 6th spark plug cylinders and it was throwing me an 0300 multiple misfire too. I'm just waiting on the new valve cover to come in now.

Seriously hoping mine isn't as serious as some of you guys too