THE M3 IS GETTING THE ANRI BUILD TREATMENT - Blown headgasket to build thread

[ChapterM3]

Short update - I got the car back yesterday evening. Drives fine, except for the misfires at idle on startup. Car idles just at or above 1k for a few minutes after being started, then settles at its normal 750rpm. Drives super smooth and no other indications of a 50 psi difference in those 2 cylinders, but I have to believe what that shop told me. They also drove it about 45 miles in total apparently to check for misfires coming back and in general to feel the car out. 45 miles seems excessive though, don't you think? Overall I'm super down about the whole thing as I really had no idea this was about to come up.

Something just doesn't add up to me of why 3,4, and 5 would be misfiring if the break in the HG is indicated between 5 and 6 - if anyone knows the answer of why this is occurring, that would help settle my mind. That or do another leakdown to see if its actually the right numbers?

Here are some photos of the plugs that they pulled and a short video of it driving - they all have oil on the threads, but all look to be worn the same - I have no idea which ones are 5 and 6 as they're not labeled, but from what I can tell they all have the same wear on them. For now it'll be parked under its cover until I can get this thing worked on.

[Arith2]

45 miles is an extended test drive. They were making sure if something went wrong, it'd be with them, not you. That's not an abnormal thing to do, especially with a very specific issue like yours. There's also the cascade effect where just because one problem caused a misfire doesn't mean there cant be more. Misfires will throw off the balance of the engine and cause other cylinders to misfire. You have to think, the misfire detection is based on the sensor data. With a leaking headgasket, there is a leak in two cylinders the entire four stroke cycle. It can't always detect the misfire accurately. The fuel trims are also trying to adjust for the leaks and that can also screw up other cylinders. Your DME didn't know your headgasket was blown, it just knows what the sensors tell it. It sounds like your car is fixed and I wouldn't stress until there's a problem. Breathe easy and enjoy your car.

[ChapterM3]

45 miles is an extended test drive. They were making sure if something went wrong, it'd be with them, not you. That's not an abnormal thing to do, especially with a very specific issue like yours. There's also the cascade effect where just because one problem caused a misfire doesn't mean there cant be more. Misfires will throw off the balance of the engine and cause other cylinders to misfire. You have to think, the misfire detection is based on the sensor data. With a leaking headgasket, there is a leak in two cylinders the entire four stroke cycle. It can't always detect the misfire accurately. The fuel trims are also trying to adjust for the leaks and that can also screw up other cylinders. Your DME didn't know your headgasket was blown, it just knows what the sensors tell it. It sounds like your car is fixed and I wouldn't stress until there's a problem. Breathe easy and enjoy your car.

Thank you for this, I needed to hear that, and it makes sense. The car however is not fixed - I didn't have them do the headgasket as I can't throw $6k at the car right now (that was their quote to me for doing just the top end) - so although it seems like it's driving totally OK, it's still driving on 120psi in both 5 and 6 apparently, and so for the time being I'm parking it and not driving it until I can get it fixed - I don't want to keep driving it and have it get worse if that makes sense

[George Hill]

They also drove it about 45 miles in total apparently to check for misfires coming back and in general to feel the car out. 45 miles seems excessive though, don't you think?

45 miles is nothing in my shop, just a fyi. I had a car come in that was misdiagnosed as needing a headgasket (M54) and the client had already approved and engine replacement but I was skeptical of the failure so I probably drove it 40 miles on the diagnosis to find out it had a bad crank case vent valve. After fixing it I put another 45 on it to verify. It then came right back with a bad brake pressure sensor (previously replaced URO brand, not by me) and I put another 40 on it just making sure it was truly good to go. If you trust your shop don't sweat the miles they are sorting your car. If you don't trust them, then maybe they are going to lunch, lol.

Honestly from everything you had stated I would get a second opinion and not tell the 2nd shop anything that the first shop told you. Go in and tell them what you observed like you did the first shop and see what they say. IF the come to the same conclusion you have your answer.

Anri what is your method for test a fan clutch operation?

[cobra]

I would do a leakdown for my own peace of mind.

If it's driving fine then I wouldn't worry and just keep driving it.

[sapote]

The car however is not fixed - I didn't have them do the headgasket as I can't throw $6k at the car right now (that was their quote to me for doing just the top end) - so although it seems like it's driving totally OK, 1. it's still driving on 120psi in both 5 and 6 apparently, and so for the time being I'm parking it and not driving it until I can get it fixed - I don't want to keep driving it and have it get worse if that makes sense
2. Something just doesn't add up to me of why 3,4, and 5 would be misfiring if the break in the HG is indicated between 5 and 6 - if anyone knows the answer of why this is occurring, that would help settle my mind.

1. Yes, try not to run the engine until it's fixed, as the leaking hot combustion gas can eat through the metal more (head and block if leaking between 5 and 6 thin wall).
2. When the 5 and 6 misfired, this could affected the crank rotational speed and many times caused the incorrect misfire detection on the other normal cylinders.
3. All of the plugs look the same and not too bad. I would have a second shop to check.

[ChapterM3]

45 miles is nothing in my shop, just a fyi. I had a car come in that was misdiagnosed as needing a headgasket (M54) and the client had already approved and engine replacement but I was skeptical of the failure so I probably drove it 40 miles on the diagnosis to find out it had a bad crank case vent valve. After fixing it I put another 45 on it to verify. It then came right back with a bad brake pressure sensor (previously replaced URO brand, not by me) and I put another 40 on it just making sure it was truly good to go. If you trust your shop don't sweat the miles they are sorting your car. If you don't trust them, then maybe they are going to lunch, lol.

Honestly from everything you had stated I would get a second opinion and not tell the 2nd shop anything that the first shop told you. Go in and tell them what you observed like you did the first shop and see what they say. IF the come to the same conclusion you have your answer.

Anri what is your method for test a fan clutch operation?

Thank you for this input, I wonder if it's been misdiagnosed - I'll get a second opinion just as you stated, that's a great piece of advice - thank you!

I would do a leakdown for my own peace of mind.

If it's driving fine then I wouldn't worry and just keep driving it.

Yeah I think I'll either do my own or get another shop to do it

1. Yes, try not to run the engine until it's fixed, as the leaking hot combustion gas can eat through the metal more (head and block if leaking between 5 and 6 thin wall).
2. When the 5 and 6 misfired, this could affected the crank rotational speed and many times caused the incorrect misfire detection on the other normal cylinders.
3. All of the plugs look the same and not too bad. I would have a second shop to check.

1. Understood - think it's fine to go to get a second opinion or rather tow it there?
2. Even if these misfires are happening only at startup? While the car is driving it feels absolutely fine
3. I'll get a second opinion, thank you for this. I have access to a shop that I could do this on my own, I would just need to get a leak-down kit

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Thank you all for chiming in, I really appreciate it and will keep updating this thread as I discover new things about the car, stay tuned

[sapote]

Yeah, take your time and do a careful leak down test, and hopefully no leak. I still don't quite understand that a bad head gasket that only caused misfire at idle but perfectly fine during driving.

[Arith2]

Thank you for this, I needed to hear that, and it makes sense. The car however is not fixed - I didn't have them do the headgasket as I can't throw $6k at the car right now (that was their quote to me for doing just the top end) - so although it seems like it's driving totally OK, it's still driving on 120psi in both 5 and 6 apparently, and so for the time being I'm parking it and not driving it until I can get it fixed - I don't want to keep driving it and have it get worse if that makes sense

Are you able to post all the codes your getting if it's more than just the misfire codes? Headgaskets are a big job as I'm in the middle of it right now. Another engine is literally cheaper than the labor.

[ChapterM3]

Yeah, take your time and do a careful leak down test, and hopefully no leak. I still don't quite understand that a bad head gasket that only caused misfire at idle but perfectly fine during driving.

That is something that I can't get out of my head as well - wouldn't the misfires happen even while driving and the car wouldn't drive as well as it does? Driving the car back from the shop it again made me think about this point again: the car seems to be running well, sounds amazing and there are no hiccups or stumbles in the RPM range. With apparently 70% leakdown in both 5 and 6, how can that be? I would imagine the engine running much rougher than it is.

Are you able to post all the codes your getting if it's more than just the misfire codes? Headgaskets are a big job as I'm in the middle of it right now. Another engine is literally cheaper than the labor.

Below are the two reports I got on the compression, leakdown, and the misfire codes. Sorry to hear you're in the middle of it, yes they certainly sound like a PITA

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[discoelk]

Just FYI, misfire is typically calculated based on (lack of) crankshaft acceleration. Given the firing order of the S54, 1-5-3-6-2-4, it's entirely possible that the ECU will throw a code for misfire on cylinders that don't have misfire. I believe this is what sapote is getting at above.

Cylinder 3 misfire code doesn't provide any evidence against a blown head gasket. Keep in mind that you're doing further damage to the head and block if the head gasket is blown by continuing to drive the car. Maybe I've missed it but has anyone suggested looking at the coolant or testing it for combustion gasses?

[jayjaya29]

The head gasket failure is between 2 cylinders, not between cylinder and oil passage or coolant passage. The only way to test for this is via a leak down test.

You could try using a borescope with a 90 degree camera to try and see if theres any visible damage to the head gasket. Maybe shining a bright light into cyl 6 while bore scoping cyl 5 would show it.

[discoelk]

The head gasket failure is between 2 cylinders, not between cylinder and oil passage or coolant passage. The only way to test for this is via a leak down test.

You could try using a borescope with a 90 degree camera to try and see if theres any visible damage to the head gasket. Maybe shining a bright light into cyl 6 while bore scoping cyl 5 would show it.

Good point. Total brain fart.

[ChapterM3]

discoelk - Good points you raise - a blackstone oil analysis showed no signs of any head gasket material or coolant remnants in the last 10k miles, but yes as JayJaya said, it seems like it's between cylinders 5 and 6. The car is not being driven or run until I have an idea on next steps, which for me as of now is getting a second opinion on the compression test and leak-down test, which I may end up doing myself with some help

[Ryan_R]

That is something that I can't get out of my head as well - wouldn't the misfires happen even while driving and the car wouldn't drive as well as it does? Driving the car back from the shop it again made me think about this point again: the car seems to be running well, sounds amazing and there are no hiccups or stumbles in the RPM range. With apparently 70% leakdown in both 5 and 6, how can that be? I would imagine the engine running much rougher than it is

I just pulled this out of my engine a couple weeks ago. Car had no misfires or drivability concerns. Only indications that something was wrong were low dyno numbers (~30hp down from similar setups) and when I did a compression test everything was at 165psi except for cylinder 5 which came in at 145psi.
I don’t mean to scare you, just showing that sometimes bigger issues might not cause a misfire condition.