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      04-30-2018, 12:30 PM   #1
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Burnt smell after WOT (experts chime in)

Hey guys, I have been trying to figure out where the smell is coming from for a while now. I had a mechanic look at everything and there are no leaks that he can find, my engine doesn't burn oil at all and I have done all scheduled maintenance ahead of time.

The smell comes a few seconds after I let off wide open throttle to redline. It doesn't smell like burning oil and it doesn't exactly have the rotten-egg cat smell. I would say it's somewhere in the middle. It fills the cabin and also smells from behind if I am being followed. After hard drives on canyons and tracks where the car is being pushed to redline consistently, the smell goes away after the first 5 WOTs.

This is how it all started.

I was catless with a burble tune at some point and all was well until but did have a strong fuel scent which is normal when catless. I put back my secondary cat to fix that issue. I started getting a weird smell and thought initially it would be the cat burning because of the tune/burble. I decided to get rid of the burble and change the X-Pipe to a newer OEM unit with both cats on thinking the old cat just went bad. That did not fix the issue, it still smelled when WOT to redline. I then took off the tune thinking it might be the added fuel that is burning the cats but even with the OEM tune, I still get the same smell. Everything is back to stock now and the smell still comes. Anything thoughts on what it can be?
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      04-30-2018, 12:36 PM   #2
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Sounds like an exhaust leak at the exhaust manifolds or possibly an external oil leak from valve cover gasket getting onto the hot manifold.

I tend to think it's something prior to xpipe since you are getting in cabin odor. If an issue was towards the back of the car and at high speeds (obviously due to having just gone WOT) I doubt you would be able to smell it. The wind would take the smell from the back of the car away from you. Fumes from in the engine compartment can make their way into the car even at speed though.



Edit..... Have you ever changed your cabin filters? Have you tried doing the pull with the HVAC on recirc instead of fresh air? Have you tried windows up and windows down?

Last edited by eatsleepboost; 04-30-2018 at 12:49 PM..
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      04-30-2018, 12:46 PM   #3
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Quote:
Originally Posted by eatsleepboost View Post
Sounds like an exhaust leak at the exhaust manifolds or possibly an external oil leak from valve cover gasket getting onto the hot manifold.

I tend to think it's something prior to xpipe since you are getting in cabin odor. If an issue was towards the back of the car and at high speeds (obviously due to having just gone WOT) I doubt you would be able to smell it. The wind would take the smell from the back of the car away from you. Fumes from in the engine compartment can make their way into the car even at speed though.
That makes sense that it would be from the engine compartment. The X-pipe seems clean so it probably is something before the X-pipe.

Would my oil level decrease if it was oil seeping through the valve covers and hitting the manifold? That would be a good amount of oil leaving the engine for it to do that. I'll take a look at them for sure.
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      04-30-2018, 12:50 PM   #4
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Quote:
Originally Posted by GeorgeA View Post
That makes sense that it would be from the engine compartment. The X-pipe seems clean so it probably is something before the X-pipe.

Would my oil level decrease if it was oil seeping through the valve covers and hitting the manifold? That would be a good amount of oil leaving the engine for it to do that. I'll take a look at them for sure.
Valve cover gasket leaks are typically very slight and shouldn't change the oil level at all but can release enough oil to hit a red hot exhaust manifold and give off fumes. I also edited my first post.
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      04-30-2018, 12:52 PM   #5
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      04-30-2018, 12:58 PM   #6
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Exhaust leak or rubbing against nearby components would be the first thing I check, too. This is relatively easy to inspect for -- you can visually inspect all of the flanges and joints for any sort of soot. Double-check the tightness of all bolts, inspect gaskets for obvious pinching/cracks, etc. See if anything around the exhaust looks discolored or burned which would indicate the tubes are contacting something when the engine rocks on its mounts.

This theory makes sense given that you said it largely disappears after multiple consecutive hard runs on the engine, as that would heat up the manifolds and tubing to seal a very slight leak.
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      04-30-2018, 01:06 PM   #7
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I know you said it doesn't smell like oil, but if it only happens on full throttle then your crankcase breather system is probably the culprit and should be checked out.
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      04-30-2018, 01:13 PM   #8
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running wide tires? even at freeway speeds, when i was running wide tires they would rub on WOT and i could smell it in the cabin...
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      04-30-2018, 01:39 PM   #9
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Quote:
Originally Posted by eatsleepboost View Post
Valve cover gasket leaks are typically very slight and shouldn't change the oil level at all but can release enough oil to hit a red hot exhaust manifold and give off fumes. I also edited my first post.
Yup, I replaced it with a MANN filter and still occurred after. The smell gets into the cabin with the windows up but not as much as with windows down. I'm thinking maybe it is a small leak from the valve covers but they don't look bad visually.
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      04-30-2018, 01:41 PM   #10
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Quote:
Originally Posted by dparm View Post
Exhaust leak or rubbing against nearby components would be the first thing I check, too. This is relatively easy to inspect for -- you can visually inspect all of the flanges and joints for any sort of soot. Double-check the tightness of all bolts, inspect gaskets for obvious pinching/cracks, etc. See if anything around the exhaust looks discolored or burned which would indicate the tubes are contacting something when the engine rocks on its mounts.

This theory makes sense given that you said it largely disappears after multiple consecutive hard runs on the engine, as that would heat up the manifolds and tubing to seal a very slight leak.
I will check it out again. If it were leaking oil on the exhaust manifold, the smell would not disappear right? Or maybe there is a certain amount of oil accumulating on the manifold when parked and it only burns off when driven at high temps.
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      04-30-2018, 01:43 PM   #11
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Quote:
Originally Posted by deansbimmer View Post
I know you said it doesn't smell like oil, but if it only happens on full throttle then your crankcase breather system is probably the culprit and should be checked out.
Hm, can't find any threads on this. This would cause oil to go into the exhaust manifold? I'm hoping it is this since it is easier to replace than valve cover gaskets.
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      04-30-2018, 01:47 PM   #12
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Exhaust leak would also be audible, slight hissing sound underneath. How often do you drive the car hard?
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      04-30-2018, 02:17 PM   #13
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Quote:
Originally Posted by amrazM View Post
Exhaust leak would also be audible, slight hissing sound underneath. How often do you drive the car hard?
In my experience, exhaust leaks are a ticking noise -- you're hearing the individual exhaust pulses. Vacuum leaks are a hiss because vacuum is constant.
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      04-30-2018, 02:26 PM   #14
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Quote:
Originally Posted by amrazM View Post
Exhaust leak would also be audible, slight hissing sound underneath. How often do you drive the car hard?
Quote:
Originally Posted by dparm View Post
In my experience, exhaust leaks are a ticking noise -- you're hearing the individual exhaust pulses. Vacuum leaks are a hiss because vacuum is constant.
No noise from the exhaust. I think this might be more of something burning in the engine bay issue. Doing some research into what Deansbimmer said, but can't find any issues with it so not sure what the symptoms would be like. I don't have any oil consumption issues (I add half a liter of oil during a 6k oil change interval).
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      04-30-2018, 04:34 PM   #15
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Quote:
Originally Posted by GeorgeA View Post
No noise from the exhaust. I think this might be more of something burning in the engine bay issue. Doing some research into what Deansbimmer said, but can't find any issues with it so not sure what the symptoms would be like. I don't have any oil consumption issues (I add half a liter of oil during a 6k oil change interval).
Is it possible that during all of the exhaust part installs and removals that something was bent and is contacting the block or some other hot areas of the engine bay?

I have seen some pretty bone-headed stuff before, like a shop forgetting to remove some packing peanuts or bubble wrap which immediately melted all over the header.
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      04-30-2018, 04:37 PM   #16
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Mine also does this if I don't have the HVAC running and I'm WOT. Smells like something got cooked. Never really bothered me much though. Don't care to chase it down that rabbit hole anyways.
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      04-30-2018, 05:28 PM   #17
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Quote:
Originally Posted by GeorgeA View Post
Hm, can't find any threads on this. This would cause oil to go into the exhaust manifold? I'm hoping it is this since it is easier to replace than valve cover gaskets.
Failed components there would cause excessive crankcase pressure. That forces oil vapor out of the engine gaskets, potentially onto hot exhaust parts, but mostly you might just smell more crankcase vapor in your cabin, especially as the HVAC pulls outside air inside. You can research crankcase pressure, crankcase oil separator, and crankcase ventilation. When the system is working properly there should be a vacuum in the crankcase at WOT.

This isn't going to push oil into your hot exhaust stream. That wouldn't be smelled inside the cabin anyway.
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      04-30-2018, 10:08 PM   #18
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Shot in the dark here but is your trunk oem? 6 months into having my car I went catless and noticed a strong cabin smell on acceleration and deceleration. Switched back to stock exhaust and still noticed it a bit but not as strong. Car sat at the dealer for a month with them trying to figure it out (had a warranty on the car at the time). Turns out my aftermarket CSL trunk was the issue. It was vacuuming exhaust fumes and filling my cabin, the trunk had like 7/10 fitment. Switched my trunk to oem and never had the same issue.
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      07-01-2018, 05:03 AM   #19
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UPDATE: Had my mechanic (BMW master tech) look at it one more time. We checked the bottom and nothing has been contacting the headers or exhaust. I took him for a spin and he says it is not the smell of burnt oil but it's coming from the engine. We couldn't figure it out. The car is not giving any codes or burning any oil. Cats have been changed, the smell still persists. I asked him about the crankcase breather system but he says I would experience oil consumption and bad idle (what he said from what I recall) which I don't. No irregularities besides the smell. The smell is more consistent with high RPMs than WOT from what I have been experiencing lately.
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      07-01-2018, 08:41 PM   #20
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If it doesn’t smell like burning oil then what does it smell like? You can tell the difference between different materials when burning. Electrical smells, clutch/brake, even fluids like power steering smells different than engine oil when burning. So what is it? A Bmw master tech should be able to differentiate them.
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      10-16-2018, 10:09 PM   #21
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Quote:
Originally Posted by GeorgeA View Post
UPDATE: Had my mechanic (BMW master tech) look at it one more time. We checked the bottom and nothing has been contacting the headers or exhaust. I took him for a spin and he says it is not the smell of burnt oil but it's coming from the engine. We couldn't figure it out. The car is not giving any codes or burning any oil. Cats have been changed, the smell still persists. I asked him about the crankcase breather system but he says I would experience oil consumption and bad idle (what he said from what I recall) which I don't. No irregularities besides the smell. The smell is more consistent with high RPMs than WOT from what I have been experiencing lately.
Did you ever get to figure out what was causing the smell? I think I have the same issue; On high acceleration at high speed, it smells like something is burning and then disappears.
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      02-11-2019, 01:52 AM   #22
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Any updates? I have the same issues it kinda smells like oil but doesn’t, I just got add 1 quart of oil warming at 5000 miles since my last oil change.
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