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I have a 2011 Smart Passion with 85,000 miles. The other day the engine light came on and a little while later started blinking. It then started to run rough. I stopped at an Auto Zone store and they hooked up their diagnostic tool. Reading came back as a bad #2 plug. These were the original plugs so I bought a new set of plugs and an air filter. Changed the plugs tonight. The original plugs were worn to a gap of .o6o. After putting in the new plugs and changing the air filter I went for a drive of about 4 miles and she ran great. Power like new. About 15 minutes later I went to leave again and the engine light started blinking again and she runs rough again. I guess I'll go back to Auto Zone and have them read it again but was wondering if anybody here might have any ideas of what the problem might be. Thanks in advance.
Brett
 

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The 'bad spark plug' diagnostics could have been their idea of an engine miss code. It is possible you got a bad spark plug, or the coil for that cylinder is not working once it warms up, or even more severe, a drop in compression due to a valve or ring problem. When you get the code, My guess is it will be a P0302 which is actually an engine miss code and doesn't point to a spark plug, but a plug is a good starting point.

I would suggest a compression test, and either replacing the coil, or swapping with one of the others and see if the problem moves to another cylinder. I know, tough to do when you don't have a code reader, but they are fairly inexpensive for a generic reader that will work most of the time.
 

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Sounds like a valve problem in cyl # 2. Happened to me years ago on my first smartie, a 2008.
 

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Sounds like your engine is going through what mine did after it tried to have a conversation with burning (literally) oil.

Looks like you’ve already changed plugs, so next in line are the coils. First get the reading for what cylinder is missing from Autozone, then swap its coil for the coil on a working cylinder.

P0301 is cyl 1, P0302 is cyl 2, P0303 is cyl 3.

If after you swap the coils, the problem cylinder becomes the cylinder you swapped the “bad” coil to? Replace the coil and your issue should be resolved.

If after you swap the coils, the issue persists on the same cylinder as before the swap? Then you likely have a compression issue and/or carbon buildup in the #2 cylinder.

At that point, I’d use Marvel Mystery Oil and see what happens. I put MMO in my engine after all three cylinders began reporting misfires and sure enough the engine runs like a champ today. :) I also ran hotter than stock plugs for a short time, though I’m not sure what impact they had.
 

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Discussion Starter #6
Update: As I mentioned, after changing plugs last night the check engine light was still on and it seemed to run rough after a bit. I took it back to Auto Zone tonight for another check. It ran fine but the engine light was still on. It read the same code. Another Auto Zone employee asked the first one if he had cleared the code last night. He said he hadn't. I asked him to clear the code and the light went off. Just to be sure I took advice from you folks and swapped coils on cylinders 2 & 3, expecting the light to come back on at some point and I would check the code again. Went out and drove about 20 miles and she runs smooth and no check engine light now. Hope it lasts. Since I was going to change oil soon anyway I thought I might try the suggestion from Miss Mercedes about putting in some Marvel Mystery Oil to clean things up a bit. What is the safe and suggested amount of MMO to put in? Also thinking of putting some injector cleaner in the fuel to clean those too. I'll update if any changes. Thanks for all the help folks.
Brett
 

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If you get a check engine light, some will not reset when the problem goes away. the computer will sense a diminished output from one cylinder and shut it down to protect the rest of the engine. Hopefully you have solved the problem! a little MMO wouldn't hurt... I would only add one thing at a time to keep from confusing the computer too much.
 

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I would add the Marvel Mystery Oil (MMO) to the gas. The directions are on the bottle. Start with a double dose, about 8 oz. & then 4 oz. per tankful.
 

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I would add the Marvel Mystery Oil (MMO) to the gas. The directions are on the bottle. Start with a double dose, about 8 oz. & then 4 oz. per tankful.
The two times I tried MMO in the gas, I got a P0104 each time. That indicates EGR or catalyst issues so probably resulted from the oil base of the MMO not burning completely or properly.

MMO worked well in the crankcase as a mild solvent.

Sent from my SM-T813 using Tapatalk
 
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