P0300

[Subzero2012]

I need help please, I have a 2000 Millenia S. lately I have been experiencing p0300 but the car drives great and normal except for slight slow pick up. The engine light is solid and I'm getting code p0300 and also the car is running rich . I can smell gas from the exhaust at start up which is accompany by a smoke for like 5seconds


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[milly00]

Just google the code man. Not hard. Its a misfire. Most likely a spark plug.
OBD-II Trouble Code: P0300 Random/Multiple Cylinder Misfire Detected

If you got them changed recently I guarantee the shop only did the front 3 on your car and charged you for doing all 6. This is notorious on the S.

Do a simple tune-up. Spark plugs, wires, etc......

[mazda-fla]

What spark plugs are you running, what gap? The S is very particular about what plugs it likes. If it is not the plugs or the coil packs, then it might be that one of the fuel injectors is going bad. There is a wire coil winding inside the fuel injector solenoid that breaks, and the signal jumps between the break as the wire touches, but over time the gap in the break gets wider and wider, and then misfires more. It gets worse over time, until eventually you have a constant misfire on that cylider. It starts out being worse when the engine is cold or you are at idle. But when the engine gets warm or higher RPM, the coil winding expands and touches together again and starts to work.

Do you get trouble codes on any specific cylinders? PO301-PO306.

[Subzero2012]

MadzaFla, you are absolutely correct. I have a check engine light for random misfire but no flashing CE light after awhile it register to p0306 but i change spark plugs and coil. I use the NGK laser platinum 3741 with .32 gap. I need help to figure out what it's because i have change coil and plugs and it didn't fix the issue. my gas mileage is bad too but my car performance is great. What can it be. How can i check if it's my injectors. Do anybody have a write up with pictures.

[yel-low]

I have a write up in the tech section for the 2.5 but the 2.3 is essentially the same.

[mazda-fla]

If you are getting a misfire on cylinder 6, and have changed (or swapped) the spark plug and coil pack, and still get the misfire. Then the fuel injector has a broken coil winding inside the solenoid.

You can test it with a multimeter at the pigtail connector for that side of the fuel rail. Do you have the Factory Workshop Manual? It shows how to test it. I have a 99S, and the manual is wrong, it show the 2,4,6 upside down as 6,4,2 when testing. Or you can remove the screws on the plastic connector on top of the 2,4,6 side. And test each injector individually, which is probably easier because the pigtail is impossible to touch the connectors without small alligator clips.

[mazda-fla]

I'm thinking the coil winding is broken in that particular injector. If it tests at about 13 ohm, it is good. If it tests as open circuit (probably would read zero on the multimeter depending on the brand), then the coil is broken. The injector would need to be replaced.

Here is yellow's post for the 2.5. Basically you do the same thing for the 2.3, but the pinout may be different. Then my write up after that. Between the two write ups, and the factory workshop manual, you should be able to test and swap out the injector.

I replace all 6 of mine. But if you don't want to put a bunch of money into this, you could just replace the single bad one with a reman injector for less than 50 bucks.

Write up for testing How to diagnose a bad injector – (KL Engine only)

Here is my write up for replacement.

(1) Remove battery.
(2) Loosen right-hand intercooler.
(3) Remove left-hand intercooler.
(4) Remove all bolts and nuts from CAC assembly.
(5) Remove the two vacuum hoses that run under the left intake manifold and the PCV hose that runs through the intake manifold.
(6) Remove the four 6mm hex head bolts from the left intake manifold, and the two nuts.
(7) Remove the 17mm banjo bolts holding the fuel line into the fuel rail.
(8) Lift the CAC up about 3 inches, and gently wiggle out the intake manifold and fuel rail as a one piece unit.
(9) Take the unit over to a bench and remove the fuel rail from the intake manifold.
(10) Remove each fuel injector from the fuel rail. Wiggle and twist them out, you can also get them started by prying them out a few millimeters with a flat head screwdriver on the notch along the side of the injector, just a bit so you can break them loose.
(11) Clean up the injector holes in the intake manifold and fuel rail with a rag dipped in gasoline.
(12) Dip your finger in fresh motor oil and lube up the 2 o-rings on the replacement injectors.
(13) Install the replacement injectors into the fuel rail by turning left-and-right while pushing them in gently.
(14) Reinstall everything in reverse order.

You also need new copper crush washers for the fuel lines. I also replaced the fuel injector insulators (rubber/metal washers that sit in the intake manifold), but it looks like you could probably clean those up gently with a rag dipped in gasoline and reuse them.

[Subzero2012]

Thanks yellow and MadzaFl, I thinks it's the injector too. Where can I purchase one at. How much do you think a shop would charge me? So I buy a multimeter and remove the coil #6 connector and test it with a multimeter .


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[Subzero2012]

I found one at autoparts by my house and it's $49.99 but now I need to know how to take out the fuel rail. Honestly without a picture it kinda hard for me to do because this car is hard to work on and once you make a mistake that's it. And is the fuel injector for the 2.3 located by the throttlebody area? I will try to buy a multimeter and the injector tomorrow.


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[Subzero2012]

Guy honestly I'm so stressed out and frustrated with this car and the misfire. Today the engine light started flashing and it's p0306 but I already change coil and plugs. But my car performance didn't change. Now I see why mechanics are scared or shy to work on this car. I have been doing most of the work myself.


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