What causes a car to misfire?

Today I replaced all four spark plugs in my car and I notice my car car still misfires. What do you think could be the cause?

No need for rude comments! Just getting people’s opinions.

Update:

My car is a 2011 Honda Accord SE 2.4

20 Answers

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  • Anonymous
    1 month ago

    Low compression will make it run terrible, get a compression gauge and check. High miles = it's probably at the head low compression point needing a head/valve rebuild.

  • Anonymous
    1 month ago

    Never Assume that because a plug is new, it is fault free.    On my 4 cylinder I bought 4 plugs, returned 3, put in the 3, and returned 2 and THEN I WAS finished.  I had an unlucky day  with plugs as I had to catch a ride to get plugs...over & over again.  Always hang onto the old plugs because while they are not perfect the car still ran.  That means you pull the plug wire while the engine is running, if it stumbles then that plug works. Save it as an extra just in case instead of pitching them all into the garbage for the garbage truck to take away.  Better to have 5 or 6 plugs "just in case" of a possible premature failure.   This is the simplest. First you got to locate which cylinder is misfiring and that is done by when the engine idles, then pull off a spark plug wire off a plug. Grab it by its boot and wiggle it off.  If the engine  now idles rougher...or stalls You know that plug is good. So put the wire back on the plug and restart the car and pull the next wire off.   You are looking for the wire that does not matter if it is on or off the engine misfires the same.   That is your plug & piston.  You could if you have the tool, check the compression of that cylinder while the plug is out.  If you got 0 PSI then there is a problem in that cylinder(so you need to see a mechanic)   If you got 100+ psi then it is not a compression issue(engine) so you are left with fuel system or electrical. Always blame electrical first which is the spark plug and most likely that will be the correct thing to do.

    . when you pull a plug wire off a spark plug and slowly put it back you can SEE the blue spark or hear the "CRACKLE" of it sparking so the coil is working.

    It is more wordy than actions.

  • david
    Lv 4
    1 month ago

    It could be a few different things from poor timing belt set to an overly hot cylinder point that 's causing preignition or detonation in the cylinder. 

  • 1 month ago

    This may sound rude - but actually troubleshoot your car before throwing parts at it.

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  • garry
    Lv 5
    1 month ago

    timing is out , see a mechanic to fix it .make sure also you have a full tank of fuel .

  • Ron
    Lv 7
    1 month ago

    If it's misfiring then the CEL is illuminated

  • 1 month ago

    If the plugs were replaced with the correct OEM spark plugs then the coils are the next thing to test.

  • 1 month ago

    Assuming your replace all the plugs and the new plugs are all good, the problem could be the plug wires or the ignition coils.

  • Will
    Lv 7
    1 month ago

    Are you sure it is misfiring? If the idle seems rough or wacky, check if a fuel injector has gone bad. Not that the fuel injectors in a 9 year old car should have gone bad, but this just happened in my '87 Pontiac Firebird and what the engine was doing was trying to compensate for a single bad injector by pumping more fuel than needed, flooding the engine basically, and it resulted in a rough idle feeling, a sporadic oil pressure gauge, and unstable volt meter. Like I said before, I can not imagine the injectors of a car that is only 9 years old going bad as opposed to my 33 year old car which everything has been going out one by one over the last few years. 

    If it is in fact misfiring just get everything leading up to the plugs inspected.

  • arther
    Lv 5
    1 month ago

    something else is wrong with it ? What did the plugs that came out look like? can you see which cylinder is missing? Type of car and ignition system might help you get a useful answer. a bit pointless telling you to check the leads if its a coil on plug arrangement 

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