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      04-30-2022, 07:11 AM   #1
blazarov
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Smell of rich mixture (raw gasoline) - catless downpipes and Evolve stage2 tune

Hi,

I have bought a F10 M5 8 months ago and since then i am suffering from the smell of raw gasoline (like rich mixture).

I have an MHD obd2/wifi dongle and have done a lot of datalogs where AFRs seem very good - solid 14.7 on idle and low load, however if you judge by the smell it is more like 12
I know that smell is expected with catless downpipes, however it doesnt feel right at all to me. I used to have an E30 with M20 straight-six with no cat and have spent countless hours tuning its standalone ECU watching out the AFR and have never experienced such strong smell.

My clothes when i go back home literally smell like soaked gasoline which is quite frustrating.

Since i got the car i replaced all injectors and coils (just to be on the safe side - 110k km) and it seems this improved the situation with the smell a little bit, but not enough. Unfortunately the people who replaced the injectors did not reset fuel adaptations and i have done around 1000km since then and LTFT still are much higher than i would like them to be (10+ on WOT on one of the banks) I was suspecting bad injector(s) causing the closed-loop lambda control to go crazy trying to achieve average target AFR for 4 cylinders, so LTFTP fuel adaptations must be reset on injector change i believe! I have only the MHD monitor license, so can not reset them myself (it requires the flasher license)

I am wondering if my mixture is really too rich, even though log says its fine (14.7) on both banks and how to verify that.

Anyone has an idea if O2 sensor goes bad could it still seem fine, but just read leaner than actual?
Or some sort of exhaust leak which could lead to skewed O2 sensor AFR readings..?

I have asked several people around me with S63 engine and catless and all of them claim they sense no gas smell whatsoever, which also confirms my feeling that something is wrong with my car.

I plan to revert the ECU tune to stock just to confirm its not the tune.
I could also replace the O2 sensors, but looking at the logs they do not seem faulty at all - very smooth and very responsive graphs, very similar on both banks.
Car has been thoroughly checked for vacuum and exhaust leaks and mechanic claims its perfect. I also have the typical Wastegate rattle (which I suspect might also be the SSP Spec-R clutch - not sure..)

Otherwise the M5 runs very very strong, almost scary strong, especially considering the grip situation

Any ideas and suggestions are welcome and appreciated!

Last edited by blazarov; 04-30-2022 at 07:16 AM..
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      04-30-2022, 12:30 PM   #2
M5_Raz
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I don't know what people you've talked to that say theirs don't smell, but mine stinks like gas and burning oil… I love it!!

When I get on it I've heard from people behind me that there's blackish/blue smoke coming out of the exhaust too.

It's all very normal on these engines with catless downpipes.
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      04-30-2022, 03:04 PM   #3
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Yup completely normal to smell fuel with catless dp's. Reminds me of my childhood. Man i miss leaded fuel
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      05-01-2022, 01:49 AM   #4
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Mine has catless and stage 2 BM3 but I went into the custom settings and set it to catless not just high flow cats which is the standard seeing.
Mine doesn't smell except on Cold start when I stand right at the exhaust.
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      05-03-2022, 06:56 AM   #5
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I’m running catless dps and a BPM tune. No smell of fuel at all unless I leave the car idling for an extended period in the garage. Mine also uses no oil between services so no oil smell either. I was previously running an evolve stage 2 tune without any fuel smell.

So based on my experience, something isn’t right. I can’t proffer any useful suggestions. I think you should look at short term trims rather than long term trims on a WOT run. Where do your AFRs drop to after 5.000 rpm when going WOT. Mine level out at about 12.2
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      05-03-2022, 11:30 AM   #6
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you sure its a gas smell and not a oil smell? You could have an oil leak somewhere and its burning off coming through your a/c.

If you are sure its a gas smell then it could be an exhaust leak from your downpipes again coming through the a/c vents.
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      05-11-2022, 01:00 AM   #7
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Quote:
Originally Posted by ajm55 View Post
I’m running catless dps and a BPM tune. No smell of fuel at all unless I leave the car idling for an extended period in the garage. Mine also uses no oil between services so no oil smell either. I was previously running an evolve stage 2 tune without any fuel smell.

So based on my experience, something isn’t right. I can’t proffer any useful suggestions. I think you should look at short term trims rather than long term trims on a WOT run. Where do your AFRs drop to after 5.000 rpm when going WOT. Mine level out at about 12.2
Hi,
smell is definitely raw fuel as in rich mixture and not like oil.
Since i got the car Oct2021 i have done 1 oil change and it took 2 liters to top up before it was time to change the oil.

When i changed the oil i also replaced the PCV system and since then i've done 3000+ kms and oil is still on max without topping up, so i get this is a good sign.

AFR on WOT is around 12.0, here is a video of 100-200 run (this one is ~6.5sec with MDM on, my best so far is 6.24 with DSC completely off) -
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      05-11-2022, 01:12 AM   #8
blazarov
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Quote:
Originally Posted by ajm55 View Post
I’m running catless dps and a BPM tune. No smell of fuel at all unless I leave the car idling for an extended period in the garage. Mine also uses no oil between services so no oil smell either. I was previously running an evolve stage 2 tune without any fuel smell.

So based on my experience, something isn’t right. I can’t proffer any useful suggestions. I think you should look at short term trims rather than long term trims on a WOT run. Where do your AFRs drop to after 5.000 rpm when going WOT. Mine level out at about 12.2
Hi,
smell is definitely raw fuel as in rich mixture and not like oil.
Since i got the car Oct2021 i have done 1 oil change and it took 2 liters to top up before it was time to change the oil.

When i changed the oil i also replaced the PCV system and since then i've done 3000+ kms and oil is still on max without topping up, so i get this is a good sign.

AFR on WOT is around 12.0, here is a video of 100-200 run (this one is ~6.5sec with MDM on, my best so far is 6.24 with DSC completely off) -
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      05-19-2022, 07:00 AM   #9
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Quote:
Originally Posted by blazarov View Post
Quote:
Originally Posted by ajm55 View Post
I’m running catless dps and a BPM tune. No smell of fuel at all unless I leave the car idling for an extended period in the garage. Mine also uses no oil between services so no oil smell either. I was previously running an evolve stage 2 tune without any fuel smell.

So based on my experience, something isn’t right. I can’t proffer any useful suggestions. I think you should look at short term trims rather than long term trims on a WOT run. Where do your AFRs drop to after 5.000 rpm when going WOT. Mine level out at about 12.2
Hi,
smell is definitely raw fuel as in rich mixture and not like oil.
Since i got the car Oct2021 i have done 1 oil change and it took 2 liters to top up before it was time to change the oil.

When i changed the oil i also replaced the PCV system and since then i've done 3000+ kms and oil is still on max without topping up, so i get this is a good sign.

AFR on WOT is around 12.0, here is a video of 100-200 run (this one is ~6.5sec with MDM on, my best so far is 6.24 with DSC completely off) -
I had the same issue on cold start and had 3 leaking injectors. Get it addressed before they fail and damage the engine.
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      05-26-2022, 01:22 AM   #10
blazarov
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Hi,
as i stated in the original post, i have preventatively replaced ALL injectors and coils already, and that improved noticeably, but did not remove completely the smell.
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      05-26-2022, 09:59 AM   #11
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Quote:
Originally Posted by blazarov View Post
Hi,
as i stated in the original post, i have preventatively replaced ALL injectors and coils already, and that improved noticeably, but did not remove completely the smell.
You will have a slightly increased raw fuel smell on cold start with catless downpipes due to cold start enrichment. This is normal. If you run a tune with the cold start disabled, this becomes less of an issue, but increased exhaust smell is still common ( especially if started inside a garage) when using catless downpipes. If the raw fuel smell remains constant after the engine is up to temperature, and while driving, then you may have an issue with dme over enrichment compensation, generally caused by fouled mass air flow sensors or a small leak on the intake side of the turbo-chargers caused by a failing pcv system, cracks in the intake boots or seals, or an exhaust leak between the downpipe and turbocharger. The last example is hard to diagnose since under throttle, the air that would escape is leaving the sealing surface, but upon deceleration, there is change in pressure, allowing fresh air to be pulled into the exhaust stream, causing a false primary O2 sensor signal. All of which can cause long term fuel trims to be adjusted, increasing injector duty cycle and cylinder enrichment. A smoke test of both intake systems and the downpipes would rule out or confirm these potential issues.
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