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p0300 this comes usually when one of multiple cylinder are misfiring which actually means that the cylinder is not burning fuel adequately or not at all. there are many reasons for this as its one of the most wide scope code in automotive line it can start from the tip the air filter to the end the exhaust.its bit easy to diagnose if accompanied with other codes if not then the fault could be anywhere in anyform it's not that you can't fix it but it's a long procedure to narrow it down 

if left alone its a very nasty thing which can create many troubles like drivability issues

rough idle,high fuel consumption, weaken the engine mounts, ruin the catalytic converter,choke the catalytic converter which in turn will ruin the rings and fail the engine and or run the catalytic converter so hot that it could lead to a fire hazard.

the fix


The spark plugs

first off all is to pull the codes and see what actually is going on get some live reads from the diagnosis machine if its a advanced car if not then start from the basics like check the spark plugs if their ceramics been burnt at the base then it is time to change them

the air

air filter should be inspected and replaced if necessary

air metering sensor should be checked and verified if in specs

the throttle hose should be inspected for air leaks also the intake hoses and the intake manifold itself should not be ruled out too they too get bent or develop cracks that can be checked by spraying starting fluid and or carefully listen you can hear a hissing noise sometimes 

the ignition coils/plug wires

then check the ignition coils for any electricity escape burn marks it'll show up like rainbow color (if distributor less) just loosen up the ig coil and raise it a bit while the engine is running you will hear the ticks ticks at uniform speed if not then switch off and exchange with the one which does tick tick that way you can narrow it down to the ig coils or the wiring of that particular coil harness which can be corrected looking up the wiring diagram of the particular make and model if still it remain in the particular cylinder then the coil driver of the particular cylinder located in the ecm is bad

if the car is equipped with the distributor then wait for it to be dark or darken the place nicely and then open the bonnet and observe the plug wires for any lightning escape through the wires be careful though as its gonna sting real bad because of very high current

the injectors/fuel pump

it could be that the injectors are not working or its wiring could be bad that too can be checked exchanging the injectors place and again hearing the ticks of the injector using mechanics stethoscope if still not then the wiring of that particular injector needs to be looked at by using the wiring diagram also its important to remove them all and get them serviced at a good place so that you can know that the spray patterns and the spray quantity is good if still the problem persists in that same cylinder then the injector driver in the ecm is the problem

for some cars which have direct injection injectors you wont be able to do this as removing injectors in those means you have to put back new ones

the fuel pump pressure can be checked by fixing a gauge at the fuel rail and or a T joint should be put between the fuel rail and the feed pipe.

please bear in mind that if the car was standing for a long time then its better to empty the tank and start with fresh fuel.

the timing components

the timing belts or chains could skip a teeth or two and the engine will run out of timing and result in misfire like behaviour you always have to check the camshaft ,crankshaft and the balancers (if equipped) that they alin at the right timing marks (if present) you can look up the FSM's of particular engine's

the engine cylinders

to check these you have to remove the fuel pump relay so no raw fuel will contaminate the catalytic converters ( if equipped ) and stick a gauge in the spark plugs place and note down each cylinders pressure also (generally) be aware that no two cylinders pressure should be more the 20 psi apart. they should be above 80 to have a start condition for specific engine pressure please look in the manual

(to pin point ring and valve or leaking gasket problem apart you have to put oil in the cylinders to take the reading)

the exhaust

sometimes with a direct hit it crumbles or sometimes because of running hot the catalytic converter melts and chokes the pipe if it is in the right place of the pipe. it can stall or run very different then you are accustomed to as there could be very high back pressure which could alter the firing cycle


the waiver

those with heart conditions stay away from ignition components as very high voltage risk is involved.

the work explained above is very dangerous to attempt on your own.

there are many additional steps which have not been mentioned here but is not limited to like cover removal or the intake removal,timing cover removal which maybe required multiple times to complete the procedure 

 you will always need the help of someone who is professionally trained to handle this types of work. the risks involved can be of electrocution, burning (yourself or the car or the premise where you are performing these exercises ) amputation, respiratory illness, blindness 


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Would be nice if you at the very least pasted the link from where the article was copied. Credit should be given where credit is due.

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@desertdude @Gaurav google is your friend you can search articles from the internet and be kind enough to post the link here if its a word by word copy then i will be glad to remove this from here....? the only thing are the pictures that have been copied from the net


the link you posted here is from a ford manual and it is way different from what i have written please back your claims with some evidence or else have the decency to at least press the like button for my efforts and time instead of this childish behaviour 

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@shadow79 you misunderstood my comment, I was trying to help you with more info by sharing the P0300 code article written by professional and certified OBD II diagnostic expert with 25 years of experience.

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@desertdude if you can't back your spineless claim with a link please grow up some balls and apologize instead of accusing me of plagiarism

i really don't have any idea or understand how you see things from your perspective my head doesn't even reach that far up my *** 

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Relax mate, take a chill pill before you blow a gasket. 

All you had to do was say its an original piece and that would be the end of it. Absolutely no need of dragging balls and ass'es into it. 


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  • Similar Content

    • By DamasoSanoja
      What does this OBD II code mean? 
      This generic OBD2 code is set when the Powertrain Control Module (PCM) detects that misfires are present in the engine but can’t identify the specific cylinder. This may indicate an intermittent problem.
      Why does this OBD II code appear?
      The PCM is constantly monitoring engine performance in order to optimize the air/fuel mixture and achieve the most efficient combustion possible. When misfires occur, the PCM tries to isolate the source (identifying cylinder number). But when that’s not possible due to random misfires that jump from one cylinder to another the P0300 code is set.
      What symptoms may occur with this OBD II code?
      The following symptoms could be present:
      Difficulty to start the engine. Random engine misfires. The check engine light may be flashing, The engine may hesitate with varying degrees of intensity. Expect many of the symptoms typically attributed to engine misfires: poor fuel efficiency, lack of power under normal or heavy load, typical smell of gas fumes due to unburned fuel, etc. What are the causes that trigger this OBD II code?
      This code may be originated by:
      Deficient or faulty ignition system component: spark plugs, spark plugs wires, coil packs Deficient or faulty fuel system component: fuel injector, fuel pressure regulator, fuel volume regulator, fuel pump Vacuum leak in the intake manifold Leaked air bypassing mass air flow sensor Deficient of faulty emission system component: oxygen sensor, catalytic converter. Deficient or faulty auxiliary emission system component: EGR valve, air injection, EVAP Deficient or faulty crankshaft position sensor Deficient or faulty camshaft position sensor Deficient or faulty mechanical component causing low engine compression: burned exhaust valve, broken valve spring, broken piston ring, leaking head gasket, worn timing belt/chain. Defective PCM Diagnostic strategy for troubleshooting this OBD II code
      The recommended course of action to pinpoint the source of the problem is two-fold.
      The first stage is the standard information gathering:
      Using a professional OBD2 scan tool (preferably one with OEM capabilities) take note of all DTC present in memory including pending codes. Record freeze frame information (if present). Perform a manual fuel pressure reading using a proper fuel pressure gauge and adapters. This is crucial, even if the scanner is reporting the fuel pressure. Perform a manual vacuum reading using a proper gauge in the pressure regulator hose (if applies). Perform a manual vacuum reading in the intake manifold test port or in any direct vacuum hose with no direct relation to the fuel injection system (brakes, air conditioning, etc). Check for air leaks bypassing mass air flow sensor. Repair as necessary. Execute a comprehensive visual inspection with special attention to hoses and lines related to the fuel system. Execute a comprehensive visual inspection with special attention to hoses related to the vacuum system, also pay special attention to possible intake manifold leaks. Perform a test with an exhaust gas analyzer (preferably, a four or five gas analyzer).  Perform a manual inspection of exhaust system: using a digital automotive pyrometer take note of exhaust pipe temperature before and after each catalytic converter. Take note of any distinctive smell in the exhaust. Perform an engine compression test and/or a leak down test.  Query the vehicle owner about what, when and where the failure occurs. Does it happen with the engine hot? Cold? Under load? All the standard questions. Take note of the vehicle VIN and find a reliable source of technical reference. Finally, clear DTC memory and perform a complete driving cycle to activate KOER diagnostics. If the code P0300 disappears then inform the owner that one possible cause is an intermittent failure and further testing would be required until the code appears again. If the code does appear then continue to the next stage.
      The second stage is the hypothesis phase. With all information at hand, is time for testing all related components by order of importance.
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