Cylinder 3. Misfire 2015 GT

[mike Hunt]

I have 15 GT base manual. all stock except a full cat back system right around 70k on the car. 2nd owner I've had the car for about 3 years. Pretty well maintained. The Car has never had a issue until now

I go out to start the car in the morning. Instant check engine light starts flashing full limp mode. I run the code cylinder 3. Misfire so I changed the plug with A motocraft. That didn't work so I swap coils still no luck still on cylinder 3.

It seams to be at idol. If I'm at a light you can feel it start to mis and you can hear it more. Sometimes it will flash and bogged down a little bit . but most of the time the light is steady and it it runs fine. No power loss not enough that I can tell at least.

At that point I take it to a independent shop they do a diagnostic. And think it could be the intake manifold. We replaced it with a New OEM manifold misfire stayed on 3. They then boriscope it " AGAIN " they see scoring on the cilinder but it had good compression.

I end up having a friend who is a Diesel mechanic look at it and he says that he didn't see any scoring on the cylinder so I don't know which one to believe.

I have done all 8 plugs since then swapped all of the coils around cleaned the MAF and put on a new air filter. And yup you guessed it it's still there.

I'm stuck and don't know where to go from here. Any suggestions or thoughts and possibilities would be appreciated..

Thank you.... Sorry for the lengthy story. I just wanted to give all the information I could

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[Timbuck]

Has anyone done a Compression check ? I brought a $50 screw in test ( not the push kind) and found my cylinder 3 was toast it’s very quick and easy to do.

 

[mike Hunt]

I have 15 GT base manual. all stock except a full cat back system right around 70k on the car. 2nd owner I've had the car for about 3 years. Pretty well maintained. The Car has never had a issue until now

I go out to start the car in the morning. Instant check engine light starts flashing full limp mode. I run the code cylinder 3. Misfire so I changed the plug with A motocraft. That didn't work so I swap coils still no luck still on cylinder 3.

It seams to be at idol. If I'm at a light you can feel it start to mis and you can hear it more. Sometimes it will flash and bogged down a little bit . but most of the time the light is steady and it it runs fine. No power loss not enough that I can tell at least.

At that point I take it to a independent shop they do a diagnostic. And think it could be the intake manifold. We replaced it with a New OEM manifold misfire stayed on 3. They then boriscope it " AGAIN " they see scoring on the cilinder but it had good compression.

I end up having a friend who is a Diesel mechanic look at it and he says that he didn't see any scoring on the cylinder so I don't know which one to believe.

I have done all 8 plugs since then swapped all of the coils around cleaned the MAF and put on a new air filter. And yup you guessed it it's still there.

I'm stuck and don't know where to go from here. Any suggestions or thoughts and possibilities would be appreciated..

Thank you.... Sorry for the lengthy story. I just wanted to give all the information I could

Has anyone done a Compression check ? I brought a $50 screw in test ( not the push kind) and found my cylinder 3 was toast it’s very quick and easy to do.

Not that I'm aware of the shop said that it had good compression but did not give me a value or a number.. I was heading in that direction. Do I have to pull all of the plugs or can I just pull a few to get a baseline

 

[mike Hunt]

Not that I'm aware of the shop said that it had good compression but did not give me a value or a number.. I was heading in that direction. Do I have to pull all of the plugs or can I just pull a few to get a baseline

Thank you for the reply

 

[Timbuck]

Sounds like they might of already did a compression test if they stated that it was good. Personally I’d check it again to give you peace of mind , and yes you can just do a few but why not do them all to give you a good base line.
Weird they would replace the inlet manifold that the last thing I’d do.

Make sure there is no broken wires to that coil and also to the injector on that cylinder.

Also worth checking that cylinder 3 fuel injector isn’t stuck or blocked.

 

[Wsvi]

mine did the same thing on cylinder #1 ended up being a broke ring land on the piston ,had a 12% psi compression loss on that cylinder

 

[mike Hunt]

mine did the same thing on cylinder #1 ended up being a broke ring land on the piston ,had a 12% psi compression loss on that cylinder

Thanks for the info.
That's what I'm leaning towards after doing more research I'm starting to think it's cooked.

I picked up a compression test kit from harbor freight and I'm going to do it today after golf if I'm still sober enough or tomorrow when I sober up... lol... I'm hoping for a miracle but judging by your two stories I'm pretty sure I'm done for with no warranty.

Happy Easter

 

[MyStang]

Did you move the coil pack to another cylinder to see if it follows or is it still misfires on cylinder 3 with a different coil pack?

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