Check Engine Light - P0304 - North American Motoring

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Check Engine Light - P0304

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Old 03-06-2019, 01:30 PM
motoring-58
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Check Engine Light - P0304

All, Today my amber check engine light came on, and engine began running rough - same time I was accelerating to enter the freeway.
Later I stopped at the car parts store and had the code read by the tech as P0304. Mini is one-owner 2012 Cooper S with 56,000 miles and was under extended factory warranty until last year, so all factory maintenance should be up to date.

Now for the puzzler...
I always use premium fuel in my Mini, but about 2 days ago I stopped at a gas station I don't normally use and accidentally tanked up with regular. This might mean nothing?? So later today I bought some octane booster and added it to the fuel, didn't make any difference to the light or improve drive-ability.

Where to go from here?
a) Should I swap coils between cylinders 3 & 4 and check to see if the code changes?
b) Could I have a tank of bad gas? should I have it drained, and change the filters? How could I test this theory?

Any assistance is appreciated, Thanks.
 
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Old 03-08-2019, 05:51 AM
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Yes swap coils is a good test. Clean the wire terminals, check the plugs carefully. Look for cracks in the ceramic. I doubt that the fuel is causing it.
 
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Old 03-14-2019, 02:01 PM
motoring-58
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Appreciate the response. I swapped the coils between 3 & 4, still ran rough, but the code changed to P0303, so starting to look electrical. First bought new plugs, all were pretty worn and need of change. #3 plug was wet when pulled. After changing plugs still ran rough, so i bought a new coil and changed it out on #3 and all is good now. I'm guessing I saved myself a few few bucks by doing this myself, plus the satisfaction of man over machine.

Thanks for the help, Joe.
 
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Old 03-14-2019, 02:32 PM
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Yep, bad coil. The swap trick is an easy diagnosis test. Glad you found it.
 
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Old 03-14-2019, 02:52 PM
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Can anyone explain to me why it's always the #3 coil position that deteriorates (and not 1, 2, or 4)? This evidently is a common problem.
 
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Old 03-14-2019, 03:31 PM
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Can anyone explain why my R52 will start on the second crank even when it’s been sitting overnight in 20 F weather but I can go in a store for 15 min, come out and it won’t hit a lick after 5-10 seconds of cranking? Turn it off and then it will start right up. Always starts right away when it has been sitting overnight. Hit and miss when it’s hot. Lots of quirks to these vehicles.
 
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Old 03-14-2019, 03:52 PM
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Originally Posted by motoring-58 View Post
Appreciate the response. I swapped the coils between 3 & 4, still ran rough, but the code changed to P0303, so starting to look electrical. First bought new plugs, all were pretty worn and need of change. #3 plug was wet when pulled. After changing plugs still ran rough, so i bought a new coil and changed it out on #3 and all is good now. I'm guessing I saved myself a few few bucks by doing this myself, plus the satisfaction of man over machine.

Thanks for the help, Joe.
At 56K miles I'd be tempted to replace all coils. If one has gone bad the others might not be in that good of shape.
 
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Old 03-14-2019, 04:47 PM
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Single coils go bad sometimes. Just let em run till they die.
 
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Old 03-15-2019, 06:17 AM
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Originally Posted by Tgriffithjr View Post
Can anyone explain why my R52 will start on the second crank even when it’s been sitting overnight in 20 F weather but I can go in a store for 15 min, come out and it won’t hit a lick after 5-10 seconds of cranking? Turn it off and then it will start right up. Always starts right away when it has been sitting overnight. Hit and miss when it’s hot. Lots of quirks to these vehicles.
I always wait a few moments to let the fuel pump build up pressure before I start the car.
It's a leftover technique from the original cars that had an SU fuel pump in the boot (trunk!). Once the click-click-click stopped you knew the carburettor bowls were full.
 
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Old 03-15-2019, 07:21 AM
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Originally Posted by MVPeters View Post
I always wait a few moments to let the fuel pump build up pressure before I start the car.
It's a leftover technique from the original cars that had an SU fuel pump in the boot (trunk!). Once the click-click-click stopped you knew the carburettor bowls were full.
Done that too, but it doesn’t explain why it starts immediately, without hesitation after it has sit all night. Literally I can turn the key to start and it will fire on the second revolution of the starter and run great. Runs great otherwise except it won’t usually start if I let it sit for over 5 minutes. Fuel pump is new. There is a loss of fuel pressure though after the fuel pump shuts off. It drops to zero. Haven’t figured out yet where the bleed off is.
 
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