Hello,

After getting gas today my mazda 6 started struggling to accelerate and shaking pretty good after which the check engine light appeared. When I checked the error code it points to random misfire (P0300) I tried replacing all the spark plugs (to no avail). Does anyone have any suggestions about what else to try next ? Maybe the crankshaft positioning sensor or ignition coils ? The check engine light has since disappeared after replacing the spark plugs but the car the car is still shaking even when idle and struggles to accelerate past 20 mph.

Any help is much appreciated, thanks.

 

Welcome to the forum


Unfortunately that universal DTC P0300 is sort of like a commuter talking and saying "there is or maybe an issue not confirmed and not in my program to exactly identify".

I would recommend STOP replacing random parts until you confirm what the problem is and was caused by!

*The first thing is to check for any more DTCs, also the monitors to see if any are in fault. Clear all DTC and reset monitors. Restart engine after it completely cools off which is generally overnight. Restart drive and see what if any DTC gets generated.
*ALWAY connected directly to the OBDII Diagnostic connector.

This is the best suggestion for a DIY. In the shop, me personally would be plugging in the Solus..

PS for all other getting the fuel was most likely not the cause and simply the act of turning off the engine and then restarting it. The except would be if the tank was run completely empty and the system had no fuel anywhere and even then maybe? I don't think diesel or E85 was accidently used instead of gasoline either.

 

Find someone with a scan tool that can display individual Cylinder miss fire counts. This may help you determine which cylinder is to blame. I would be getting a fuel sample examined by a experienced mechanic.

 

Ok turns out coil pack on cylinder 2 is bad and swapping the coil pack moves the problem to the new cylinder. Confirmed this by unplugging coil pack with the engine running and noticing NO change in idle. Should I replace ALL the coils (4) or just the bad one ?

Thanks,

 

Before you buy new coils......
Odd that you did not get a DTC relating to the first condition and then none when you swapped the coil??
I would swap it one more time and then do a coil check using a digital volt/ohm meter.

 

The check engine light didn't come back on after swapping all of the spark plugs, for some reason it went away without me forcing it to be cleared. I also didn't drive it to try and get the light to come back on. It was pretty obvious that the issue persisted, car was still shaking on idle and didn't respond well to throttle. As a side note, my dad helped with all this and he has converted manual trucks to automatic before so he knows a thing or two. Appreciate all the help guys !

 

Thats easy it is the other way around that is challenging...

Ok well I hope you get it solved and back up and running well.


As for the P0300 if you read why that TC is used then you would understand why it did not return after you swapping coils.