Dealer says Low Compression Cylinder 8

[moses19]

Hey guys looking for some advice here. Yesterday car threw a Cylinder 8 Misfire and Misfire on Startup code. Took the car into the dealer and they said cylinder 8 has low compression(see pictures). I was hoping that at worst it would be the Intake Manifold issue thats pretty common, but it doesnt seem to be.

They gave me 2 options. Order a longblock and be done with it or do a teardown and see what potentially might be wrong. Car has the Ford Performance Power Pack 2 and exhaust, that is it. Only symptoms were a slight rumble at idle and a weird start up. Also, I am out of warranty so unfortunately im going to have to eat the cost. Any advice? Any specific questions I should ask them? What would you guys do? Thanks.

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[Smunczen]

Did you contact Ford Performance and ask them about helping with warranty repairs. Just a thought.

 

[moses19]

Did you contact Ford Performance and ask them about helping with warranty repairs. Just a thought.

Hmmm you think they would help with anything? Not sure it was because of their tune. Never had any problems and always used 93 octane.

 

[ice445]

Cracked ringland on #8 is common, its the cylinder that often gets the hottest due to how the cooling circuit is designed. Detonation damage to the piston or scoring of the liner is also possible. Given the amount of labor to tear it down, I'd at least do a leakdown test to find where that compression is going. If it's going into the crankcase then you'll just want to order a new shortblock.

 

[moses19]

Cracked ringland on #8 is common, its the cylinder that often gets the hottest due to how the cooling circuit is designed. Detonation damage to the piston or scoring of the liner is also possible. Given the amount of labor to tear it down, I'd at least do a leakdown test to find where that compression is going. If it's going into the crankcase then you'll just want to order a new shortblock.

Thanks for the reply, I'm not too saavy when it comes to in depth workings of an engine.

So I can ask them to do a leak down test? What would be the other outcome if it's not going into the crankcase? If it's going somewhere else would that mean something else is broken?

 

[CJJon]

Mileage? Still paying on it? Do you want to keep it long term?

 

[ice445]

Thanks for the reply, I'm not too saavy when it comes to in depth workings of an engine.

So I can ask them to do a leak down test? What would be the other outcome if it's not going into the crankcase? If it's going somewhere else would that mean something else is broken?

I would ask them to do one. Plus borescope #8 for a visual inspection. It's unlikely, but a bad valve or seat could be the problem. A new head is cheaper than a long block by a lot.

The test they did is called a power balance test, its accurate but doesn't determine the cause. No real tear down is necessary to get a good idea of what happened.

 

[moses19]

Mileage? Still paying on it? Do you want to keep it long term?

Yeah still paying on it, and would like to keep it long term. Nothing else really interests me at the moment. 55k miles bought it at 27K miles.

 

[moses19]

I would ask them to do one. Plus borescope #8 for a visual inspection. It's unlikely, but a bad valve or seat could be the problem. A new head is cheaper than a long block by a lot.

The test they did is called a power balance test, its accurate but doesn't determine the cause. No real tear down is necessary to get a good idea of what happened.

Awesome man thanks for the info. So in your opinion in which situation should I ask for a short block vs a long block?

 

[CJJon]

Did you get a quote? Gonna be spendy. Short block cheaper.

When you are done you will have a nice fresh motor!

 

[Blwnsmoke]

Yeah still paying on it, and would like to keep it long term. Nothing else really interests me at the moment. 55k miles bought it at 27K miles.

What year? More then 5 years old?

 

[moses19]

Did you get a quote? Gonna be spendy. Short block cheaper.

When you are done you will have a nice fresh motor!

Yeah teardown itself is about 1,800 plus finding the issue and fixing it. Longblock and install us about 9k

 

[moses19]

What year? More then 5 years old?

Yeah unfortunately, it's a 2015

 

[btcarmd]

All they have done is a relative compression test and power balance test. I would want to see actual compression on that cylinder as well as leak down test. Then you could better determine best repair.

 

[moses19]

All they have done is a relative compression test and power balance test. I would want to see actual compression on that cylinder as well as leak down test. Then you could better determine best repair.

You're right. But I think it's safe to say that the relative compression test show there's something wrong there? They also switched around the plugs and the issue stayed at 8.

Definitely asking for a leak down test tomorrow. Do you know what the possible outcomes of that can be?

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