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2003 nissan maxima p0300

ok so i recently bought a 2003 nissan maxima 134k and i bought it with the p0300 check engine light on a looked at the engine and though it was an air box problem because they had previously installed a K&n filter so i wen to the junk yard and got a 2000 nissan maxima air box and new filter i changed the oil and checked the spark plugs they look new and the dates on the coils are 2012 and 2013 and still its misfiring. i bought it to a mechanic and he discovered a vacuum tank had previously broke and they glued back together so i replace that with a factory one today same problem still misfiring but it got better but now its a p0306 then i erased the code and p0304 came back i earsed it then p0302 came back then i change the cam sensors, and the crankshaft sensor and now it get a p0300.

*when sitting for a long time HARD TO START ( takes mutplie cranks to start it )
but once i leave it off for short time like 30 min it starts rigth up no problem

  • when stop at a stop light in drive i can feel small little explosions
    sounds like my car is beat boxing
    *performance is strong good acceleration no problem on that i just don’t want it misfiring

Get the compression checked, and post the results

Also have that mechanic hook up a fuel pressure gauge. This is what he should check

Pressure key on engine off
Pressure key on engine idling
Check the fuel pressure regulator
Does the pressure hold after the engine is shut off
Measure the resistance of the injectors . . . might have an open or a short
Do an injector balance test . . . do they all flow the same, is one leaking, is one restricted?

I hope you’re not driving it like this . . . the misfires may soon damage the catalytic converter

Most misfire problems on this car stem from not using Nissan parts. We always get the plugs and coils from the dealer on this model.

The small explosion sound at idle may be engine pinging. Causes can be spark plug electrodes too wide, distributor cap/rotor problem (if your car has those), ignition or valve timing too far advanced. ---- Edit: And using the incorrect octane rating for the gasoline. — It’s unusual to have noticeable pinging at idle without something seriously askew. Pinging is more often a complain only when the engine is under load, like going uphill.

i went to the mechanic today and he tested the cylinder 2,4,6 for compression and they were all normal he also check the power to the injectors and it was good however when we pulled out the spark plugs out they were black and the gap was bigger he also said that they used autolite not ngk what nissan uses. i remember pulling them out before they where looking new but i broke one of the coils pulling it out so now it idles rougher and im in the process of waiting for my shipment of that coil to come in but he has no idea whats causeing the starting problem


So you’ve got misfires on bank 2 only . . . the side closest to the radiator, I believe

if those plugs are black, it sounds like they may be fouling out due to some rich condition

What about that fuel pressure testing?

In my opinion, the autolite plugs are NOT the problem. If they were, the other bank would also be misfiring, and that doesn’t seem to be the case

Yea it only on bank 2 I never got a misfire code for cylinder 1,3,5, and we couldn’t check the fuel pressure easily because the 03 maxima does not have a port on the gas line to test it you would have to hook it up to to the fuel pump but he said because I didn’t have a problem with it. due to me not having reduced performance it wouldnt be the fuel pump and yesterday I was installing door speakers and came across a receipt dated 2-14-14 saying changed plugs and coils customer brought his own parts $150 labor the mechanic also so said the coils were cheap so any ideas I’m see if I can switch out my moms 03 pathfinder coils with my coils and drive it to see but give me your ideas.


I never really thought the pump was the problem

Food for thought . . . depending on where the fuel pressure regulator is located, if it’s faulty, it might be starving bank 2 for fuel

I’ve actually seen this, but on a different engine

In any case, you’d have to do some hard core diagnosis to confirm this, or disprove it

As far as the coils go, does each cylinder have its own coil, or are the coils “double sided”

If each cylinder has its own coils, I kind of doubt they are the problem. In that case, I would expect both banks to have misfires

OK and and each cylinder has its own coil and the exhaust in the more when I turn it on smells like gas and I see a small cloud of white smoke and it pops not like a continueous flow I’m guessing that’s from the misfire

The coils are not the problem, because if they were, both banks would be missing . . . in my opinion

Popping noises could be from unburned gasoline getting into the exhaust and igniting in the tail pipe. Or from an exhaust leak. An exhaust leak can confuse the fuel injection computer and result in too-rich operation. The only fix is to repair the leak. Have you asked your mechanic what they think is causing the popping sounds?

I like George’s idea

An exhaust leak on bank 2 would cause the PCM to command additional fuel for that bank only. And that could result in fouled plugs, which would lead to a misfire on bank 2 only

Now that you mentioned that exhaust leak I did notice at the bottom of the car the flexi pipe was rusted and that the mesh covering the spring was starting to move Away from the end I’m take a pic so you see can see it but I didn’t here any loud noise from the exhaust I’ll also record the starting up in the morning and thanks a lot guys I really want to save this car its really nice

What about a partially clogged converter on one bank? That can cause spark plug blackening and fouling.

OK here’s what I’m talking about