[Catalin335xi]

Hi all,

I have this issue with my car for more than a year now in trying to find this.

The issue: car initially runs perfect. after staying in heavy traffic for more than 20-30 mins the rpms starts to fluctuate and AFRs go up and down, being correlated by STFTs going to -34% on both banks until the rpm goes back up. So for some reason it tends to go very rich which drowns the engine. If I let it sit like that it starts stuttering so bad that it can even stall. If it stalls sometimes it has a very long crank afterwards followed by a huge black cloud of smoke on startup. If I start driving it hard for a while, when I stop and let it sit at idle it runs great and again after 10-15-20mins it begins the fiasco again. In wot it runs great.

I tried changing a lot of parts:
new o2 sensors
all injectors idx12
new hpfp from bmw
new lpfp
new ekp
new crankshaft pos sensor
new coils plugs
new silicone vacuum lines
new fuel tank recirculation valve (or whatever it's called, the valve that connects from the tank to the intake manifold to burn off excess gas vapours)

NO error codes. The car always sits in Fuel Mode 2 (normal).
I've completely ran out of ideas.

My initial thought was "ah simple, injector leaking", but I tested all of them by connecting them backwards and cranking the engine to see if they leak and none of them do. Secondly, if there was an injector fault, I should see weird AFRs on one bank, not both and in an identical manner in each. The AFRs also mirror each other almost perfectly.

My second guess was the hpfp. But sadly getting a new one directly from BMW had no impact. Also, when the engine stalls and it struggles to crank back up the HPFP reading is 6-700psi so it is not a fuelling issue that prevents it from starting.

What could cause so much fuel (or so little air) at idle if everything fuel related is good and I have no vacuum leaks? Also, why on earth does it happen only after the car sits at idle for a long time, and is not more consistent?

Thank you for your time reading this and I hope you have some ideas to help me.

[Bimmer_Bro]

Originally Posted by Catalin335xi

Hi all,

I have this issue with my car for more than a year now in trying to find this.

The issue: car initially runs perfect. after staying in heavy traffic for more than 20-30 mins the rpms starts to fluctuate and AFRs go up and down, being correlated by STFTs going to -34% on both banks until the rpm goes back up. So for some reason it tends to go very rich which drowns the engine. If I let it sit like that it starts stuttering so bad that it can even stall. If it stalls sometimes it has a very long crank afterwards followed by a huge black cloud of smoke on startup. If I start driving it hard for a while, when I stop and let it sit at idle it runs great and again after 10-15-20mins it begins the fiasco again. In wot it runs great.

I tried changing a lot of parts:
new o2 sensors
all injectors idx12
new hpfp from bmw
new lpfp
new ekp
new crankshaft pos sensor
new coils plugs
new silicone vacuum lines
new fuel tank recirculation valve (or whatever it's called, the valve that connects from the tank to the intake manifold to burn off excess gas vapours)

NO error codes. The car always sits in Fuel Mode 2 (normal).
I've completely ran out of ideas.

My initial thought was "ah simple, injector leaking", but I tested all of them by connecting them backwards and cranking the engine to see if they leak and none of them do. Secondly, if there was an injector fault, I should see weird AFRs on one bank, not both and in an identical manner in each. The AFRs also mirror each other almost perfectly.

My second guess was the hpfp. But sadly getting a new [...]

Trying cleaning both your Vanos solenoids or possibly replace them. Make sure the o-ring is also in good shape as that alone can cause issues. This is just a guess but you should try cleaning them with break cleaner to see if the symptoms improve.

[Catalin335xi]

UPDATE: found the issue - for some reason my charcoal canister gets flooded with fuel and when the EVAP purge valve tries to release "vapors" into the intake it actually releases liquid gas which drowns the engine. Temporarily fixed it by unplugging the purge valve wire connector and leaving the tank refill cap slightly open to allow extra pressure to escape.

[The_E92_Fan]

Woah that’s wild. How’d you figure it out?

[lowrydr310]

Interested in this as well. Usually the charcoal canister only gets flooded with fuel when you overfill your tank.Whats causing it?