2018 Mustang Ecoboost Check Engine Light Issues.

[zShadox-]

Hello, around 3 weeks ago I got the check engine light with code P0303 misfire on cylinder 3 and had a Goodyear shop solve the issue under the dealers expense, they replaced the active grill shutter and the check engine light was gone. Now about 2 weeks after the check engine light came on when I started my car with same code P0303 misfire on cylinder 3, which could be the issue now? The car has 42,900 miles on it and it's my first car so I would appreciate any information that can be provided, Thank y'all.

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[Deleted member 35644]

Ok, let me start by saying WTF is up with tinkering with the grille shutters to fix a misfire? DO NOT EVER TAKE YOUR CAR THERE AGAIN.
Let a Ford dealership diagnose and repair the issue, which could be one of several things, like a coilpack, spark plug, fuel injector, etc. Anything on with that cylinder that is part of the combustion process can be the cause. Grille shutters, not so much.

 

[ORRadtech]

Where is your coolant level?
Any odd odors in the exhaust on start up?
Any unusual smoke/steam/mist from the exhaust on cold start?

I don't know your comfort DIY level but if you want to make some diagnosis yourself try;
Switch coils #3 & #2 - or whichever you choose. Does the code change to where you moved the #3 coil?
Pull the #3 spark plug and compare it to another.
Or take it to a competent mechanic and ask for a borescope of #3, a leak down test and check the coolant for exhaust gasses.

The bad news, in short is, you're looking for a headgasket leak. Something these 4 cylinders are prone to.

 

[zShadox-]

Ok, let me start by saying WTF is up with tinkering with the grille shutters to fix a misfire? DO NOT EVER TAKE YOUR CAR THERE AGAIN.
Let a Ford dealership diagnose and repair the issue, which could be one of several things, like a coilpack, spark plug, fuel injector, etc. Anything on with that cylinder that is part of the combustion process can be the cause. Grille shutters, not so much.

Yeah that's exactly what I thought when they told me that, as long as I didn't have that light on I was ok with whatever they did. Good thing I wasn't the one that paid $1200 for that repair lol. I just hope is nothing serious, and thanks for the reply

 

[zShadox-]

Where is your coolant level?
Any odd odors in the exhaust on start up?
Any unusual smoke/steam/mist from the exhaust on cold start?

I don't know your comfort DIY level but if you want to make some diagnosis yourself try;
Switch coils #3 & #2 - or whichever you choose. Does the code change to where you moved the #3 coil?
Pull the #3 spark plug and compare it to another.
Or take it to a competent mechanic and ask for a borescope of #3, a leak down test and check the coolant for exhaust gasses.

The bad news, in short is, you're looking for a headgasket leak. Something these 4 cylinders are prone to.

I just checked and coolant is under it says MIN. Also today when I started up the car in the morning there was white smoke or mist coming out, not sure if it's because it was really cold outside.

 

[ORRadtech]

Yeah that's exactly what I thought when they told me that, as long as I didn't have that light on I was ok with whatever they did. Good thing I wasn't the one that paid $1200 for that repair lol. I just hope is nothing serious, and thanks for the reply

Yeah those people were pretty useless IMO.
I wish you luck but mine started the same way P0303. Three months later Ford returned the car to me after a headgasket replacement. Don't be surprised if that's what you face.
The good news is if you're under a warranty, it's covered.
Oh, and don't dawdle on this. If it's the a coolant leak as I suspect, it WILL destroy your catalytic converter too.

 

[ORRadtech]

I just checked and coolant is under it says MIN. Also today when I started up the car in the morning there was white smoke or mist coming out, not sure if it's because it was really cold outside.

Get an appointment with Ford asap to have them diagnose it. I recommend calling tomorrow.

 

[zShadox-]

Get an appointment with Ford asap to have them diagnose it. I recommend calling tomorrow.

Oh God, I will make sure to call tomorrow and get that appointment. I also just checked and still have every warranty from factory until august of next year, bumper to bumper is expired already. I also have the warranty from the dealer I got the car "Carmax". Do you think factory warranty will cover it just in case? Also should I tell Carmax that I want my car to be serviced at a ford dealership specifically? Btw how could I check for a coolant leak?

 

[ORRadtech]

I don't recall the factory warranty details. The power train warranty may well still be in effect. A Ford dealer can tell you. If it's still under a Ford warranty then I'd have them do the work.
I don't know what to say about the Carmax warranty. It certainly won't hurt to call them and ask.
As for the coolant leak question, reread my first post. Those things will point you to an answer.
On mine I could see coolant drips with a borescope. T hen Ford did a leak down test and verified exhaust gas in the coolant. I also sent an oil sample to Blackstone who confirmed traces of coolant in the oil.

 

[zShadox-]

I don't recall the factory warranty details. The power train warranty may well still be in effect. A Ford dealer can tell you. If it's still under a Ford warranty then I'd have them do the work.
I don't know what to say about the Carmax warranty. It certainly won't hurt to call them and ask.
As for the coolant leak question, reread my first post. Those things will point you to an answer.
On mine I could see coolant drips with a borescope. T hen Ford did a leak down test and verified exhaust gas in the coolant. I also sent an oil sample to Blackstone who confirmed traces of coolant in the oil.

Alright, I will make sure to have them check everything. Thanks for your time, really appreciate the help.

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