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Check engine light appears twice in 8 days

13razorbackfan

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8 days ago I purchased a 2018 GT Premium 5.0 convertible automatic with right at 38k miles. Someone obviously drove it a ton in 2 years and it is super fun to drive.

So when I first started the car at the dealership the check engine light came on but drove it around anyways checking it out. Other than some small rock chips in the black paint the car is in excellent shape. I told the dealer I would make him an offer once I found out what the check engine light was all about. So he drove it around to service and said due to it being sitting on the lot for a week or so without it being so much as started it had a cold start misfire. It had been getting down in the low 20's all week and in the low to mid 40's as the high. So they cleared the code, I made a offer and after some negotiations bought the car. Love it to death.

Been driving it every day since I bought it, it has been warmer outside probably in the high 50's and even a couple 70° days. Then all the sudden yesterday the temps drop. Didn't drive the car at all yesterday because it was Thanksgiving and stayed home all day. Before I forget the car is not in my garage but outside in the elements.

Get in the car this morning and notice the check engine light is on again. Take it back to dealer and same thing. Cold start misfire cylinder one although I don't remember if I was told when I bought the car if it was the same cylinder. Talked with a tech and he said that it's possible that low grade gas was put in the car and then left to sit. He said that could be all it is. Said the computer showed it started a little rough then after a few seconds would even out. He said it probably needs a new plug/coil and if it did it again they'd replace it. Being the Holidays I didn't want to leave it over the weekend.

Having said all that I own a lawn and landscape business and run nothing but ethanol free gas in all my equipment to keep it from collecting moisture and gumming up and destroying fuel lines and other rubber components in these small air cooled engines.

When i bought the car they drove it down to the gas station and filled it up I'm guessing with the cheapest lowest grade fuel they could find in my case that 87 with ethanol mix. I ran it down to about 1/4 or a bit less during those warm days I was driving every day then stopped to fill it up with 93 ethanol free gas. This was Tuesday I believe then all the sudden the cold hits again, car sits for 36 hours and it throws the code.

So what are y'alls thoughts on this? Keep driving it and using the 93 octane ethanol free gas and if it throws that code have them replace the plug and/or coil? I'm a newbie so take it easy on me fellas
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Lime1GT

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The car is designed to run on 87 octane which can have I think up to 10% ethanol so that shouldn't be your problem. Look in your owners guide for fuel spec. If you want help here you have to tell us the code/s produced. Clearing the code as the dealer did twice then sending you merrily on your way will not fix the problem. If you take it back again get them to show you the code, find a person/shop to read it to you or buy a cheap code reader to find yourself. The dealer should have looked after you better. No sense throwing parts at it until the code/s are listed.
 
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13razorbackfan

13razorbackfan

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The car is designed to run on 87 octane which can have I think up to 10% ethanol so that shouldn't be your problem. Look in your owners guide for fuel spec. If you want help here you have to tell us the code/s produced. Clearing the code as the dealer did twice then sending you merrily on your way will not fix the problem. If you take it back again get them to show you the code, find a person/shop to read it to you or buy a cheap code reader to find yourself. The dealer should have looked after you better. No sense throwing parts at it until the code/s are listed.
Yes I agree. My brother has a code reader he's bringing tomorrow. I want to get the code to reproduce itself so I can get them on it asap. I am a very squeaky wheel so I'll make them fix it right which they should have already but I digress
 

drive_55_not

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1st thing I'd change the plugs,, Then the intake, there's been several that have had their's replaced due to them being cracked.

.
 
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13razorbackfan

13razorbackfan

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1st thing I'd change the plugs,, Then the intake, there's been several that have had their's replaced due to them being cracked.

.
Yeah I saw a video where there is a rod that goes down each side of the intake that is opened by an actuator. This one particular intake the right side rod had snapped off even through the actuator was activating the rod wouldn't open the butterfly valves correctly thus throwing the random misfire code. That's why I want to see what specific code the car is throwing with my own eyes. I'd do it today but my brother decided to wait till tomorrow to drive in town with the reader and besides I've having some paint correction done to take out some small chips and swirls on the black paint. I bought a DA and some pads along with Meguiers 105 and 205 so I can start doing this myself in the future.

But I do agree plugs then intake
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