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.

Typically the misfire code is triggered by a failed/failing coil.

The knock sensor code is likely trigger by the misfire.

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.

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.

Agreed. Cheap and easy. Be sure to use the right NGK plugs.

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.

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..

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.

Now how about those front spark plugs?

:sprint: o, and welcome to the p 0300 club, enjoy!!!!! :D

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.

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.

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.

Looks like bad luck on these injectors. Sucks but looks like it's getting towed. Time to do it all over again...

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. fuk, and my optima yellow top is also going south, dammit!!!!

Maybe you damaged an oring, maybe you need to use the ole school timing light to ensure it's not a ignition coil issue!

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.

Update Y'all, the car is back up and running! Ended up being the injectors, the replacement ones on the other cylinders were still stuck open causing it to run rich resulting in black spark plugs. Flow testing and making sure they're spraying correctly is key to avoid flooding the cylinders and making sure it runs smoothly. Hopes this helps out fellow members out there with this fuel problem! Just know even if you replaced your injectors, they could still be defective! Don't go out replacing other parts when in reality it could be just bad injectors.

Items replaced:
-All 6 Injectors
-All 6 spark plugs
-New oil, Flushed out coolant and put in new coolant, flushed brake fluid, put in new fluid. Brakes work much better now with new fluid! old was dirty and haven't touched in a couple yrs.
-Intake manifold gasket
-Intake boot (old one was hard as a rock)
-New air filter
-New Fuel filter
-New Coolant Hoses
-Draining out gas from cylinders due to stuck open injectors.
-Refilling the tank with new gas

Took it for a drive for 3 hours, even sat overnight, couple days etc and starts up the way it should. It runs beautifully! No overheating or anything. Being that it sat for 3 1/2 months of not moving/starting.

I'm glad to hear you FINALLY took our advice and your Max is back on the road. :)

Josh, glad you finally took Wizards advice. That SoCal dude knows. I think you should always flow test new injectors, since so much junk is now on the market..... lots of fakes out there.

Mind telling us where you got your new (and old) injectors from so some others don't go down the same road?

I was about to spring for new NGK iridium plugs off of amazon the other day, 6 for $34 seemed like a great deal:


But then I read the comments and several posted that they were counterfeit NGKs that caused problems when installed-- if you compared them side by side vs actual NGKs there were some subtle differences you could spot confirming they were fake. Amazon sure doesn't seem to care....