Rebuild or Replace motor?

[Gturo_5.0]

So I've had my 2011 5.0 for about 6 months. I bought it with 85k miles and now its at 92k. A couple of months ago my cyl 8 started misfiring so I pulled the plug and noticed it was black asf, so I changed all of them. 3 days later my misfire comes back so i pull the plug again. Oil. Damn. So cylinder 8 is done. When i bought it, guy said it had a BAMA 91 Race tune and an Airaid Intake. Guessing the tune is what did the most damage. Anyway i get a misfire at idle and a quick puff of smoke out of the exhaust pipe from bank 1. So i'm guessing its the rings. Specifically the oil control rings. That's based off of basically just a guess. So my question is, in this case do I get another engine? Or can i just get that one piston ring replaced? Not that i can affored either right now lol.

 

[Revvv]

Without putting a borescope down the hole it's hard to say. You could possibly get away with a cylinder hone and a new set of rings. Then again, you could have something else that can only be assumed.

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[Silbult14]

Don't be too quick to decide #8 is shot. A bad coil pack on that cylinder will cause a misfire and oil and carbon on the plug. Try moving a coil from one of the other cylinders to #8 and putting the #8 coil to wherever you got the coil from and see if the misfire code changes cylinders. If it's still #8 then a compression test, leak down test and bore scoping it would be in order. If any one or all of these three tests indicates a problem then a tear down is the next step. If all the other cylinders check out good, just fixing #8 might be OK, but considering the mileage and not really knowing about the first 85,000 miles a complete rebuild might be in order. Another option would be a low mileage used engine with a warranty. Several years ago I bought a 3.8 six cyl. with 52,000 miles for my old '01 SN95 DD from LKQ for $550.00 with a six month warranty. It's still going strong now with over 200,000 miles on it. I am sure a Coyote will be a good deal more, but it might still be cost effective.

 

[Riddick]

a leakdown test will tell you if there is an issue and where it is. If it's oil it could be as simple as a bad valve stem seal. Don't assume the worst. I'd do a compression test and leakdown before deciding anything.

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[Gturo_5.0]

Don't be too quick to decide #8 is shot. A bad coil pack on that cylinder will cause a misfire and oil and carbon on the plug. Try moving a coil from one of the other cylinders to #8 and putting the #8 coil to wherever you got the coil from and see if the misfire code changes cylinders. If it's still #8 then a compression test, leak down test and bore scoping it would be in order. If any one or all of these three tests indicates a problem then a tear down is the next step. If all the other cylinders check out good, just fixing #8 might be OK, but considering the mileage and not really knowing about the first 85,000 miles a complete rebuild might be in order. Another option would be a low mileage used engine with a warranty. Several years ago I bought a 3.8 six cyl. with 52,000 miles for my old '01 SN95 DD from LKQ for $550.00 with a six month warranty. It's still going strong now with over 200,000 miles on it. I am sure a Coyote will be a good deal more, but it might still be cost effective.

So i changed the coil packa around and its still cylinder 8. I don’t appear to be burning an insane anount of oil, and i honestly havent noticed any power loss. The misfire is there sometimes and sometimes it runs fine which is whats werid to me. I’m just assuming the worst because i dont want to get disappointed when i finally find out what it is. I dont know how to do a leakdown test, but i can check the compression. What is the dynamic compression supposed to be on these motors? 210ish psi?

 

[Silbult14]

A leak down test can be quite useful, but the test equipment is more expensive than a simple compression tester. A leak down test also requires a source of compressed air which not everyone has. Since you can do a compression test I would start with that. Make sure you have all the plugs out and either remove the throttle body or block it wide open so there isn't any restriction and make sure the battery is fully charged so you have plenty of cranking power for all 8 cylinders. I don't know what the factory compression spec is, but ideally all cylinders should be within 10% of each other. Just for example, if # 8 is 120 psi and the other cylinders average 200 psi then clearly there is something wrong with #8. If this turns out to be the case I would squirt a tablespoon or so of clean heavy weight [ at least straight 30 weight ] motor oil in #8 and crank # 8 again and see if the pressure comes up significantly. If it does you probably have a ring seal problem. If it dosen't do much, one or more valves aren't sealing. Good luck and let us know what you find.

 

[Gturo_5.0]

A leak down test can be quite useful, but the test equipment is more expensive than a simple compression tester. A leak down test also requires a source of compressed air which not everyone has. Since you can do a compression test I would start with that. Make sure you have all the plugs out and either remove the throttle body or block it wide open so there isn't any restriction and make sure the battery is fully charged so you have plenty of cranking power for all 8 cylinders. I don't know what the factory compression spec is, but ideally all cylinders should be within 10% of each other. Just for example, if # 8 is 120 psi and the other cylinders average 200 psi then clearly there is something wrong with #8. If this turns out to be the case I would squirt a tablespoon or so of clean heavy weight [ at least straight 30 weight ] motor oil in #8 and crank # 8 again and see if the pressure comes up significantly. If it does you probably have a ring seal problem. If it dosen't do much, one or more valves aren't sealing. Good luck and let us know what you find.

Okay so i havent had much time to do my compression test yet but i noticed something a bit strange today. When i turn on my car after work it runs smooth as butter, i let it idle for 15 minutes and let it warm up completely and it still runs like a champ. I then drive home (about 10 miles) and when i get home it’s misfiring very harshly and my exhaust has a weird smell. I’ve never smelled sulfer before but it certainly doesn’t smell like oil. Then i turn it off for no more than 2 minutes and turn it back on. Now its running smooth as hell again. What? That doesnt sound like a piston ring issue to me. But im not very experienced. Sounds more like a catalytic converter problem. What do you guys think?

 

[basspro302]

Definitely not a cat problem. You could have a faulty coil or injector possibly. Sometimes coils and injectors will fail when hot.

 

[MG0h3]

Since money is an issue I'd borrow a compression tester from an auto parts store. Check the orings before you leave.

If it's fine, you still may want to do a leak down. If it's not and comp is low, safe to assume you have a mechanical prob.

3 days for the code to pop again is a little long for a coil or injector. Plus I'd expect to have a rich/lean code for that bank as well.

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