P0300 Random Misfire Code

[marisp]

I've been getting the P0300 code popping up on my OBD computer for some time now and am having quite a bit of trouble pinpointing the problem.

Started back in December, when I got it sitting idling for some time in a snowstorm in Vermont. Came on once, and after clearing it, it didn't return until late January again. Happened again in February, then a second time in February, then a few times in March. Next thing you know its coming up a couple times a week. Finally decided to get a tune up done, and changed the plugs, distributor cap, wires, fuel filter etc. Code came up again right after. Also did the timing belt, tensioner, and water pump. Cleaned up and oiled my aftermarket air filter and checked my mass air flow sensor to see if it was acting up. Seems fine. Problem seems to have gotten worse and worse and for about the last month, it comes up virtually everytime I drive now. It's not blinking, just comes up when the engine is warmed up and i'm in stop and go traffic in the city, i.e. I stop at a light. The problem never occurs on the highway, as i've recently drove up north 3 hours and back without a hitch, and 2 weeks ago Toronto to Montreal and back without the CEL coming on. The truck does have a slightly rough idle at times, and shortly after is when I get the CEL. I have a small crack in my exhaust manifold, but doubt that has anything to do with it. In any one trip, if I clear the code at a stoplight and continue driving, the code does not come up again until I shut the engine off and drive somewhere again, meaning, it never comes up 2x in a trip.

I've asked a couple people what they might think it is, even took it to a dealer, and after an hour of looking at it, they were able to replicate the problem and bring up the code, but they can't tell why its happening, and told me that instead of changing all kinds of parts, I should wait until the problem worsens. I figure its pretty bad now already, as it comes up everytime I drive!

Anyone have any idea what might be causing this?

[Adam]

My dads r50 has a similar issue. It will run ok for about 20 seconds then you can feel that somethings not right and the CEL comes on and starts blinking and then goes solid (it has an evap code too) when you start to drive again. We did a tune up, timing belt and all that as well. The shop said it's the cat's that are plugged up partially and the engine can't push the exhaust out properly at idle. I don't know if I believe that but maybe it will help you.

[marisp]

Thanks. I have a few month old custom exhaust with new cats. Mine doesn't blink and runs just fine as beyond the light and idle, you wouldn't think anything was wrong. The idle is only slightly rough, in that there is a minor shake to the truck, that doesn't always happen, but seems to go hand in hand with the CEL.

[marisp]

ugh....P0300...clear...P0300...clear...P0300...clear...P0300...clear... (since my last post)

Anyone?

[sandor]

I had a 0306 (misfire on cylinder 6) about this time last year. Nissan techs here in town suggested a few things including a fuel injector service. Before breaking down and getting them to clean the fuel injectors, I poured a can of seafoam in with the fuel, and let the engine inhale some more seafoam through a vacuum line, and a few days later it went away and never came back.

Possibly you have dirty injectors?

[marisp]

I had a 0306 (misfire on cylinder 6) about this time last year. Nissan techs here in town suggested a few things including a fuel injector service. Before breaking down and getting them to clean the fuel injectors, I poured a can of seafoam in with the fuel, and let the engine inhale some more seafoam through a vacuum line, and a few days later it went away and never came back.

Possibly you have dirty injectors?

Every now and then, the code came up P0304. But when I say, every now and then, I mean like 4 times out of the 50 i've got the CEL in the past few months. Otherwise, its random. I can try Seafoam or a similar product to see if it works. Thanks for the tip and your experience. Could be its injector related. Got to start narrowing this down somehow...

[marisp]

Got a couple of cans of Seafoam, and plan to use it in every way to see if it helps with my problem...can in the fuel tank, a little in with the oil before an oil change, and also wanted to try and get some into all cylinders through a vacuum line. On the last point, that's where I need some help. Where is the vacuum line that I would pour a little into?

[superchargedx]

Hey there,
I acually have been having the p0304- #4 misfire code coming up myself for ages!!! seems to only happen when the weather
changes (not in the wet weather if your thinking plug wires LOL.... cold to warm). Had a Nissan tech tell me that he has seen alot of our generation se/sc 's with some sort of a small coolant leak that dribbles from the intake manifold into cyl #4??? Has anyone else heard of this??
I am a tech myself, and we have recently been using seafoam alot at work with great success!!! Plan on using it in my fuel tank and through vac line just before next oil change!!!

Dont know if any of this will help...... just thought I would mention my issue also to see if any of the Nissan guru's have heard of this issue??

Sean

[Simon]

Yep, the VG33's are common for that leak. There's an o-ring that deteriorates and allows coolant to seep out near the throttle body. The part is pretty ridiculously priced, as the whole thing has to be replaced, as Nissan doesn't just sell the o-ring.

[marisp]

Well, so far i've been running a can of Seafoam added in to a 1/2 full tank for 2 days and have not seen the CEL come on yet. Lately it would come up on every drive. I've even been driving more aggressively to see if I can force it to come up, but so far so good! I'm starting to think it must have been something injector related, as I do find the car idles better now, and seems generally a lot more responsive (almost like it was a few years younger).

I added some Seafoam to my oil too this morning, drove about 50kms around the city, and then got an oil change. Oil was pretty dirty. Truck seems much happier.

I still do want make some smoke signals for my neighbors and let some in through a vacuum line, but not sure which one it is...any pointers to the right hose would be appreciated.

[Jayman]

I still do want make some smoke signals for my neighbors and let some in through a vacuum line, but not sure which one it is...any pointers to the right hose would be appreciated.

Search for the seafoam how-to thread, there are a few pics of which ones you can use...

[superchargedx]

Thanks Simon!! How much approx is that part?? And how much of a pain is it to replace??
Any info would be great!!

Thanks Simon,

Sean