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P0300 Random misfire

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Old 10-10-2018, 09:07 PM
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P0300 Random misfire

155k miles..Hello y'all I had a misfire issue that came up about a month ago or so. The car was flashing NON-STOP while driving. The codes were P0306 on old injectors and P0301 due to stuck open injector after replacement..

So what I did was replaced all injectors and that seemed to fix the problem only for 20 miles. Check engine light came back on flashing with a misfire, bogging on idle, missing like crazy. Realized one of the injectors was stuck open, o2 sensors running rich all the time and the spark plugs in the rear were bad.

Fixed the injector that was stuck open, replaced both o2 sensors, replaced rear spark plugs.. Now the car drives beautifully!! However. When coming to a stop it misses sometimes, also has a hard time starting sometimes, I also noticed there's a beating rhythm coming from the exhaust... No smoke whatsoever...

I drove it on the highway 50 miles, did some stop and go traffic... The car ran so smooth...Then I turned off the car, turned it back on. Left it on idle and the check engine light came back on flashing for maybe 30 seconds. I took it for another drive for 50 miles and the check engine light remained SOLID.. No more flashing. The car remained to drive smooth and did not misfire like crazy but can tell it has that little bit of "miss" going on... I feel like there's something that isn't functioning as it should and I think it may be one or two more things to really smoothen things out. Pulled the codes and It came out to

-P0300 Random misfire
-P0325 Knock sensor.


With that being said, should I drive this car with the check engine light being remained solid and no more flashing? Or should I address this random misfire before I drive this car further? It's driveable, it's smooth, doesn't bog like crazy anymore, however in idle it has a bit of miss going on, No noise going on, has a starting issue sometimes but still turns over. But not smooth as I imagined it to be...Any advice on what the problem can be would be greatly appreciated.

Last edited by JoshG; 10-10-2018 at 10:13 PM.
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Old 10-11-2018, 05:17 AM
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Typically the misfire code is triggered by a failed/failing coil.

The knock sensor code is likely trigger by the misfire.
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Old 10-11-2018, 09:42 AM
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You mentioned replacing the rear spark plugs.

Is there any reason why the front ones were not replaced at the same time?

I'd replace the front ones now. Might solve your problem.

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Old 10-11-2018, 09:50 AM
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If I'm understanding your story correctly, you installed 6 new injectors and the flashing cel issue went away. But the car still had missing issues and you determined that one of your new six injectors was bad so you replaced it. Now the car is almost perfect but still has a slight miss and is slightly hard to start. I think the answer is clear, one of the six injectors is still not operating perfectly.

Since the CEL is not flashing, I'd say it probably ok to drive until you get it fixed for good.

What was your source of the six new injectors?

Haven't you replaced your coilpacks with genuine parts within the last year? I don't this is a coilpack issue. It's still an injector issue IMO.
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Old 10-11-2018, 09:51 AM
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Originally Posted by JvG View Post
You mentioned replacing the rear spark plugs.

Is there any reason why the front ones were not replaced at the same time?

I'd replace the front ones now. Might solve your problem.
Agreed. Cheap and easy. Be sure to use the right NGK plugs.
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Old 10-11-2018, 04:18 PM
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I had the front ones replaced roughly 2 years ago and they're still fairly new. So they were left alone. The rears were all rusty. I also had replaced all 6 ignition coils back in June of '16 with HITACHI. They haven't given me any issues within those two years until this came up.

I also took the car for a drive today, It's starting to miss alot more on idle and not as smooth as it was yesterday, It rev's beautifully... I also noticed the whole exhaust system is shaking like mad... The exhaust has a beating rhythm to it when standing in front of it with no smoke coming out from it. Though the CEL remains SOLID.. No more flashing.. It's not a pleasant drive at all. I don't feel like driving it until it gets fixed.

What should I do from here..?

Last edited by JoshG; 10-11-2018 at 04:22 PM.
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Old 10-11-2018, 04:27 PM
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Originally Posted by JoshG View Post
I had the front ones replaced roughly 2 years ago and they're still fairly new. So they were left alone. The rears were all rusty. I also had replaced all 6 ignition coils back in June of '16 with HITACHI. They haven't given me any issues within those two years until this came up.

I also took the car for a drive today, It's starting to miss alot more on idle and not as smooth as it was yesterday, It rev's beautifully... I also noticed the whole exhaust system is shaking like mad... The exhaust has a beating rhythm to it when standing in front of it with no smoke coming out from it. Though the CEL remains SOLID.. No more flashing.. It's not a pleasant drive at all. I don't feel like driving it until it gets fixed.

What should I do from here..?
Clear the codes. Start car and let it idle. Go for a short drive. With any luck, the specific cylinder will identify itself......ie 0303. All it takes is one bad injector to cause your symptoms.

You also didn't confirm my understanding of what has transpired, and where you got your injectors.
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Old 10-11-2018, 04:28 PM
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Originally Posted by The Wizard View Post
If I'm understanding your story correctly, you installed 6 new injectors and the flashing cel issue went away. But the car still had missing issues and you determined that one of your new six injectors was bad so you replaced it. Now the car is almost perfect but still has a slight miss and is slightly hard to start. I think the answer is clear, one of the six injectors is still not operating perfectly.

Since the CEL is not flashing, I'd say it probably ok to drive until you get it fixed for good.

What was your source of the six new injectors?

Haven't you replaced your coilpacks with genuine parts within the last year? I don't this is a coilpack issue. It's still an injector issue IMO.

Correct, 6 injectors put in, one of the 6 was stuck open, replaced both o2 sensor due to the computer reading it was running rich all the time, rear spark plugs replaced. It still misses on idle after all those were replaced. CEL remains SOLID.. Has a hard time starting too but still turns over.. Starting to miss more on idle after a day of replacement and CEL still remains SOLID... Though it's not representing a p301-p306 code.. Just a P0300 Random misfire code..

Last edited by JoshG; 10-11-2018 at 04:33 PM.
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Old 10-11-2018, 04:32 PM
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Originally Posted by The Wizard View Post
Clear the codes. Start car and let it idle. Go for a short drive. With any luck, the specific cylinder will identify itself......ie 0303. All it takes is one bad injector to cause your symptoms.

You also didn't confirm my understanding of what has transpired, and where you got your injectors.

I cleared the code yesterday after having the CEL on for 50 miles. It drove beautifully at the time. Though It eventually triggered the CEL and still presents P0300 Random misfire. Cleared it again, took it for a drive, starting to miss worse than before.. triggered the CEL again but remains solid.. Random P0300 Misfire.

When the injector was stuck open. The car would misfire like crazy and the CEL would Flash NON-STOP while driving.. This isn't the case anymore as far as the CEL no longer flashing while driving.

Also the injectors I used were Hitachi, new O rings as well.

Last edited by JoshG; 10-11-2018 at 04:38 PM.
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Old 10-11-2018, 08:39 PM
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Now how about those front spark plugs?
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Old 10-11-2018, 09:21 PM
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Originally Posted by Turbobink View Post
Typically the misfire code is triggered by a failed/failing coil.

The knock sensor code is likely trigger by the misfire.
o, and welcome to the p 0300 club, enjoy!!!!!
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Old 10-12-2018, 03:03 AM
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I have the Torque app. It can tell you fuel trim numbers. I read up on it and those numbers can tell you about lean vs rich system.

Can you check into fuel trim? It might really give you solid answer. And o2 voltage readings.

Try BG44k fuel treatment. If one of the injectors is dirty for some reason it should clear it up. But your injector is new so idk.

Or buy 2 new coils and start swapping rears and fronts for isolation if it's coil.

Last edited by MichMaxFan; 10-12-2018 at 03:05 AM.
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Old 10-13-2018, 02:34 AM
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Originally Posted by max ride 41 View Post
o, and welcome to the p 0300 club, enjoy!!!!!
yeah honestly it sucks... I have not got to drive the car much due to this problem for almost a month and a half now. I'm getting frustrated and want it fixed. :/ I honestly thought after the stuck open injector, o2 sensors and rear plugs was going to smoothen things out. but nope.

im honestly thinking my catalytic converter is shot... idk I could be wrong. I have the original exhaust that is 24yrs old!! It has a large crack across the whole thing so i don't know if thatll effect any air flow.. I think the car needs some exhaust work at this point because I have not touched it at all.

With some new exhaust I think the car would run 20x better.. it's running on 24yr old orginal parts!! I think it's tired by now.. lol. The damn entire exhaust system is shaking so bad that it shouldn't be.. it's annoying the crap outa me. Lol

Last edited by JoshG; 10-13-2018 at 02:38 AM.
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Old 10-13-2018, 04:18 AM
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Are you going to keep the car?

If so, feel good about putting a little $$ into it, replacing old parts.

I’m not necessarily a proponent of throwing parts at a fix, but you’re right ... some of these parts you’re thinking are contributing to your issues are 24 years old. I don’t consider replacing those parts, failed or not, as a waste.

I’d likely start by replacing the coils ... all of them.

If I’m not mistaken a full set of 6 Hitachis are available from Rockauto for about $220.00
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Old 10-13-2018, 09:51 AM
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I've had some interestingly good luck with old original coils running copper NGK 6953 BKR5E-11 V-Power Plug. Copper plugs provide the best spark, they just don't last as long as other harder metals.

So I need to change them every 25,000 miles (2 years), but I like to check on how my plugs are burning and if there are any valve cover oil leaks at that interval anyway. No big deal.

Also at approximately $12 for a set, the price is right.
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Old 10-13-2018, 11:43 AM
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Originally Posted by Turbobink View Post
Are you going to keep the car?

If so, feel good about putting a little $$ into it, replacing old parts.

I’m not necessarily a proponent of throwing parts at a fix, but you’re right ... some of these parts you’re thinking are contributing to your issues are 24 years old. I don’t consider replacing those parts, failed or not, as a waste.

I’d likely start by replacing the coils ... all of them.

If I’m not mistaken a full set of 6 Hitachis are available from Rockauto for about $220.00



yes I do plan keeping the car because of it's condition it's in. The paint job still shines, no body damage,little rust on the car. Now if it had paint issues, body damage, rust, a whole list of problems then I'd dump it by now but that isn't the case. Clean 4th gens are becoming harder and harder to find as time goes.

I've already replaced a lot of things on the car and when I get to fixing it it's either old or on original parts. I don't wanna give up on this car because of a misfire..this isn't also my only car. It once was my only car but I have another car that isn't as old as this because the car is going to break time to time and I needed something fairly newer just in case the maxima is down.

Last edited by JoshG; 10-13-2018 at 11:50 AM.
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Old 10-20-2018, 04:28 AM
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This started to come out of the exhaust, it has a beating rhythm to it.. it's white smoke. And lots of strong fuel smell.
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Old 10-20-2018, 04:30 AM
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Hey y'all I need some advice here.. so I started the car after a week of it sitting and now it just has white smoke coming from the exhaust... lots of strong fuel smell. This is the worst I've ever seen the car at. but again it's an old car so something is tired and needs to be replaced.
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Old 10-20-2018, 04:40 AM
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Injector(s) failure.
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Old 10-20-2018, 05:36 AM
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I'd figure it's that... but I replaced all 6 with hitachi. One of them was stuck open.. fixed that.. now back to square one. Is it ok if I drive it 10-15 miles to get it where I need to or have it towed? This whole thing became more of a mess than it should. so disappointing.

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Old 10-20-2018, 05:47 AM
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Your symptoms are classic injector failure.

I’d surmise that the liquid spewing from your exhaust not only smells like raw fuel, it is raw fuel.

Am I right?

Perhaps something got damaged, displaced or mis-aligned during installation of your new injectors.
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Old 10-20-2018, 11:26 AM
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Josh,
I said it once, I'll say it again. It's your injector(s) still. Just because you replaced 7 of them doesn't mean you're out of the woods. Wherever you bought them from, it's clear you got bad ones.
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Old 10-20-2018, 12:34 PM
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Looks like bad luck on these injectors. Sucks but looks like it's getting towed. Time to do it all over again...
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Old 10-22-2018, 11:53 PM
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i had the fuel smell josh, replaced the 2 front 02 sensors and crank sensor and iacv. i finally got a specific code for the p0300, it was p0304. cylinder 4 misfire. yay!! i'm hoping it's a coil and not an injector. just replaced the 3 rear injectors a few months ago. replacing my plugs soon as well, they gotta have at least 25 to 35,000 on them. o, and i had to spend 410.00 to replace my transmission cable that took a crap on me 2 weeks ago. ***, and my optima yellow top is also going south, dammit!!!!
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Old 10-23-2018, 06:38 AM
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Maybe you damaged an oring, maybe you need to use the ole school timing light to ensure it's not a ignition coil issue!
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Old 10-23-2018, 08:20 PM
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My brother’s 3.5 swap is plagued with this code but no flashing CEL. Just the rough idle and similar exhaust tone.. I’ve done new valve cover gaskets, spark plugs, coil packs, rail and FPR with injectors, upper/lower/elbow and TB reseal along with fuel pump and fuel filter. He’s got codes for both front O2s as well but don’t think they’d throw off the ECU enough to throw a P0300.. Plan on doing a smoke vacuum leak test and going from there.
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Old 10-24-2018, 12:03 AM
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02's will def make the engine light come on, usually a p0300 like i had. i also have to do a coil and new plugs. just did 2 front 02 sensors and the car runs better, almost done i hope.
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