# 2015 Fiat 500 Sport Misfire



## 110year_old_fixer (Feb 7, 2021)

Hello,
So I have a 2015 Fiat 500 sport with 102k miles. Three days ago I started my car and got a violent misfire. I checked the OBD2 and got p0304 misfire cylinder 4. My first go to was to replace the coil pack. Once the coil was replaced I started the car everything was running smooth for a couple days. Now I’m getting a much more soft misfire still from cylinder 4. 
My spark plugs where changed at 94k miles so that’s only around 8k miles on the plugs.

-Is it possible that when the coil pack went out it caused some damage to the plug? 
OR
-Should I start troubleshooting the fuel injector?
I do run Lucas high mileage fuel injector cleaner ever few fill up.

Thanks for your input and advice.

p.s.
Just to be clear I’m not have random misfires only cylinder number 4.


----------



## HotRodx10 (Aug 24, 2017)

I would start by pulling the spark plug and replacing it. Also check the plug wire and boot for any sign of scorching. New plugs can go bad, too, and when they do, they can fry the coil. It usually doesn't happen the other way around, though. I don't know if it's even possible for a defective coil to ruin a spark plug.

While you have the spark plug out, unless it's obviously bad, I would run a compression test on the cylinder. If the compression is what it should be, install the new spark plug and see how it runs. If the problem persists, my next step would be to swap the injector for cylinder 4 to a different cylinder, and see if the misfire follows it.


----------



## slipparee (Jun 12, 2017)

I had one of those cars well both a pop and an abarth quite a difference.

Anyways on the regular 500 pop/sport engine like yours has one of my cylinders would always have corrosion down inside the spark plug well. Water getting in there usually from what looked like rain. I never bothered to figure out why it was happening. I just changed the cheap copper plugs every 10k miles which was about when it would start missing.


----------



## 110year_old_fixer (Feb 7, 2021)

Sadly the plugs for my car cost 35/ea for OEM replacement.
But it dose look like rush inside the cylinders. It was in two of mine. They do have a rubber seal I was thinking about replacing those.


----------



## BigJim (Sep 2, 2008)

110year_old_fixer said:


> Sadly the plugs for my car cost 35/ea for OEM replacement.
> But it dose look like rush inside the cylinders. It was in two of mine. They do have a rubber seal I was thinking about replacing those.


Move that plug to another coil and see if it still misfires. If it doesn't, move the coil to a different plug and see if you have a misfire. At least that will tell you if the coil or plug is bad.


----------



## slipparee (Jun 12, 2017)

It is the plug. Well I mean a seal somewhere is fouling the plug getting it corroded and then it misses.

Let me know if you do find the culprit. I was never inclined enough to want to take things apart when I could just put a new plug in there and it was good for another 6 months.


----------



## 1972bigdaddy (5 mo ago)

My son has 15 500 pop non turbo. He's not mechanical in any way. He had his cel come on do he tool to dealer who said he needed a plug for #2 it was fouled. So he paid to replace it. He said he drove home 62 miles and next day cel came on after a minute and car shook violently and cel was flashing. So he didn't drive it. He called dealer they said most likely coil so he replaced that. Problem occurred 10 sec after startup. Yes the codes were reset/cleared. He decided to tow it to local shop who don't know fiats and they broke a bunch of stuff. Even cut some bracket and said its out of warranty so it don't matter. Did full tune up and replaced remaining coils and cleaned injectors and carbon in cylinders #2 had alot. They reset code and said he should be good. Well nope it happened about 5 minutes after leaving. Seems none of these shops or dealer is being definitive about the diagnosis. Anyone else who is monitoring this thread have a thought. Not sure if they did a compression test or not and the plugs weren't oily. May and map sensors checked and pcv is good.


----------



## HotRodx10 (Aug 24, 2017)

1972bigdaddy, do you know what codes were set? And when you say "it happened again", do you mean the light came on or that it started running rough?


----------

