P0300 random misfire
P0421 warmup catylyst efficiency bank 1 below threshold
P0301 cylinder misfire

 

can someone please advice me the best steps to resolve this problem does my car have individual coil packs or do they come in a pack. Also i was thinking about changing the spark plugs but i am not sure which one to go with i have 2010 mazda 6 V4 and i would lilke some help with the catalyst issue and how to fix it thanks any help would be greatly appreciated

 

The spark plugs are due to be changed at 75,000 miles. Change them now. You may also have a bad ign coil. Ign coils from dealer are expensive and are individual.

Now for the Good News : The Catalytic converters are warrantied for 96 months (8 years, 80,000 miles i believe) as per: Mazda Factory Warranty | Automotive Warranty | Mazda Canada
Provided you kept up your services.

If your car is not covered, look here: https://www.mazdaforum.com/forum/maz...3-0-ltr-30510/ and every other car.
The code comes on @ 5% inefficiency and can be cleaned, see post in above thread for more!

Do not drive very long while car is misfiring otherwise your cat will be destroyed due to the raw fuel being dumped in the exhaust and igniting in the catalytic causing it to melt: How can I tell if my catalytic converter is... — Yahoo! Autos
AND CLICK HERE: http://reviews.ebay.com/Reasons-for-...00000002803746

Click here to see how to test your cat, not easy:

 

i might add:

Make sure there is no oil in the sprk plug wells. Oil would indicate a Valve cover seal leak and the vavle cover seal would need to be replaced along with the ignition parts.

The catalytic converter may still be fone but it cant handle all the fuel coming by because of the misfires. In other words the P0420 may clear up. But why not take advantage of the warrenty?

Good luck.

 

Had my Mazda 626 for 3 yrs. check engine light started coming on going up hills and it literally crawls up hills. We have brought to several mechanics!! Reads misfires. Changed spark plugs twice, spark plug series twice, coil. Still does it. Cat converter is ok far as I know. One mechanic said due to misfire and other said due to open flap - oil? Very frustrated as no no on seems to be able to pinpoint problem. In PA and need to pass emissions test. This seems to be a common problem. Have already put in over $1500 just in parts tying to troubleshoot and everyone that scans car comes up with different codes. HELP!! It amazes me that no one has been able to actually find the problem and fix it. Next stop Mazda dealer?? Suggestions anyone?

 

I had a long reply and accidentally "X"'d it out.

READ and do it: https://www.mazdaforum.com/forum/new...-avatar-30905/

Missfires Can Be Caused By a Million and One Things,

Vac Leaks
Wiring Issues
Spark Plugs(Even Fresh Spark Plugs That Are Crappy Quality.... E3 And Such)
Ignition Coils
Alternators (Search EMI)
MAFS
Injectors
Injector O-Rings
Intake Gaskets
TB Gaskets
PCV Hoses
PCV’s
Malfunctioning EGR
Malfunctioning CAS
O2 Sensors
Aftermarket Intakes
Intake Hoses
Vac Lines
Timing Chains
Timing Chain Tensioner
Broken Cam Gears
Malfunctioning Cam Sensors
Incorrect Crank Gears(The I4 Has Like 40 Different Configurations For Whatever Reason)
Incorrect PCM Flash
Issues Within The PCM
PCM Wiring
Bad Diaphram Within The FPR
Issues Within The Fuel Pump
Dirty Fuel Filter
Dirty Fuel Lines
Pre-Cats/Poor Exhaust Flow

If the above gaskets/seals have not been changed, change them. Clean your MAF sensor, throttle body.
Change your PCV valve and probably that short hose as well.
Inspect the intake accordian tube for cracks. Inspect for vaccuum leaks.
Put in a good Fuel system cleaner: Red Line Synthetic Oil - Gasoline Fuel Additives - SI-1 Complete Fuel System Cleaner
Inspect wires. Re-set ECU after doing above.