Intense raw fuel smell and longer first cold starts, failing fuel pump?

Hey all, I've got an '08 E92 M3 with 83k miles and about a week after my last track day, I started noticing a strong raw fuel smell from the passengers side of the car. I thought it might've been a loose cap once or same bad gas, so I'm running some Techron fuel system cleaner through the system now but it doesn't seem to be going away over time. When I park the car after driving and get out, it's like being slammed in the face with gas fumes, some in cabin, most outside. There doesn't seem to be a large loss of power though. Plugs and coils have been done in the last year as well, so I don't think that's the cause of the longer start time.

I've been digging around on the forums and some posts seem to point to the fuel pump that sits under the rear seat: https://www.m3post.com/forums/showthread.php?t=1862715


The car is headed to the bodyshop for work so I won't be able to act on anything for a month or two unfortunately, but I wanted to wrap my head around the next steps.

check for a bad injector.

amrazM wrote

check for a bad injector.

Is there a way I can scan for injector health or do they need to be pulled and manually checked?

I agree it sounds like a bad injector. At 83K miles and almost 15 years old it's not a bad idea to replace all 8 injectors as preventive maintenance. I replaced mine on my 11' with 80K miles and noticed a slight bump in power.

bravehart38 wrote

I agree it sounds like a bad injector. At 83K miles and almost 15 years old it's not a bad idea to replace all 8 injectors as preventive maintenance. I replaced mine on my 11' with 80K miles and noticed a slight bump in power.

With more track use in this car's future, that's probably a sound idea.

Is it all around the car or focused near the rear? I've had both issues, injectors will smell like raw fuel on start up; fuel pump will smell towards the rear of the vehicle after a drive. Easy way to check it to pop off the back seat and see if there's any fuel collected on the top of the fuel pump

Ajolives wrote

Is it all around the car or focused near the rear? I've had both issues, injectors will smell like raw fuel on start up; fuel pump will smell towards the rear of the vehicle after a drive. Easy way to check it to pop off the back seat and see if there's any fuel collected on the top of the fuel pump

I want to say I've had it near the rear after drives, I should pop the rear seat and check that point .

It could also be a two point failure where it's both acting up since there's also some fuel smell on startup.

Yeah could be, the fuel pump housing leak (crack in my case) will make your car smell like a gas station outside the rear of the car. The top of the pump was nasty and dirty af when I popped it open - fuel and dirt mixture.

When replaced my injectors, I was getting a processed fuel smell(if that makes sense) for only a couple seconds after start up. Almost like half exhaust/half fuel smell. Either way, they're relatively cheap and easy to swap. Plus leaky injectors have taken out a couple engines on these forums over the years

Popped off the cover for the fuel pump and while it's dirty, I didn't see any fuel pooling. Maybe it is the injectors?

Cmassey3 wrote

Hey all, I've got an '08 E92 M3 with 83k miles and about a week after my last track day, I started noticing a strong raw fuel smell from the passengers side of the car. I thought it might've been a loose cap once or same bad gas, so I'm running some Techron fuel system cleaner through the system now but it doesn't seem to be going away over time. When I park the car after driving and get out, it's like being slammed in the face with gas fumes, some in cabin, most outside. There doesn't seem to be a large loss of power though. Plugs and coils have been done in the last year as well, so I don't think that's the cause of the longer start time.

I've been digging around on the forums and some posts seem to point to the fuel pump that sits under the rear seat: https://www.m3post.com/forums/showthread.php?t=1862715


The car is headed to the bodyshop for work so I won't be able to act on anything for a month or two unfortunately, but I wanted to wrap my head around the next steps.

Just a thought.. but after a decade or more the E9X gas cap simply wears out. When it does you may get a "Service Engine Soon" message occasionally in iDrive, or on the dash. The gas cap will also feel like it no longer tightens up that much. Additionally, an "Increased Emissions" or "Tighten Gas Cap" message may appear in iDrive or the dash console. Perhaps spirited driving is causing some gas to leak out of the filler. BMW redesigned their gas cap due to so many warranty claims. The new ones have a blue gasket seal. I replaced my old OEM gas cap with one of these from FCP Euro:
.

.
https://www.fcpeuro.com/products/bmw-fuel-cap-blau-16117222391

Cmassey3 wrote

https://i.imgur.com/EtYXmG7.jpg

Popped off the cover for the fuel pump and while it's dirty, I didn't see any fuel pooling. Maybe it is the injectors?

Both sides? Agreed looks fine compared to what I came across

Mine looked lovely

DrFerry wrote

Just a thought.. but after a decade or more the E9X gas cap simply wears out. When it does you may get a "Service Engine Soon" message occasionally in iDrive, or on the dash. The gas cap will also feel like it no longer tightens up that much. Additionally, an "Increased Emissions" or "Tighten Gas Cap" message may appear in iDrive or the dash console. Perhaps spirited driving is causing some gas to leak out of the filler. BMW redesigned their gas cap due to so many warranty claims. The new ones have a blue gasket seal. I replaced my old OEM gas cap with one of these from FCP Euro:
.

.
https://www.fcpeuro.com/products/bmw-fuel-cap-blau-16117222391

The string is busted on my cap anyway so this would be a good idea.

Ajolives wrote

Both sides? Agreed looks fine compared to what I came across

Mine looked lovely

I only checked the passenger side, so that's a good reminder to check the other.

If you do end up finding a grumpy injector I highly recommend running a bore scope into that cylinder to check for bore scoring. Just for peace of mind.

Header to x pipe donut gaskets, after running it hot on track they may have fell to pieces

SAMM3Y wrote

Header to x pipe donut gaskets, after running it hot on track they may have fell to pieces

Ah, I haven't heard to check there yet. Thanks for the tip.

Cmassey3 wrote

Ah, I haven't heard to check there yet. Thanks for the tip.

this seemed obvious, you would hear if you have an exhaust leak. it would sound like the exhaust is dumping right under the car.

Just dropped off the car at the body shop, but the first thing to try after it gets back is the gas cap. Had a normal startup time this morning.

I haven't heard the exhaust be louder than normal, so maybe that's intact?

Bodyshop called and said there's a likely fuel tank leak and it'll need to get fixed before paintwork begins, so I'm having the car towed to the local shop and we'll see what the culprit is.

O2 sensor.
Or a fuel delivery leak

Turns out the left side fuel hat was the leak point and that was the one I didn't check...

Back from the shop with a new left side fuel hat, no more smell in the cabin. They also tested the right side fuel hat seal and it doesn't need replacing.