Drivetrain malfunction in rain only, left bank cuts out

[DanHalen]

Hello,

Hoping someone has some insight and possibly experience with something similar- I heed help!

2018 X5M, 26k miles. Dinan tune/CAI/Akra exhaust; all have been installed since car was brand new, never had an issue. Still have stock cats.

Has ran perfect until the heavy rains a month or so ago. In the rain car started to misfire, and sometimes would throw a DTMF, cutting the left bank of the motor (cylinders 1-4). I had the spark plugs and coils changed- still did the same misfiring.
This only happens when it's actively raining or when the roads are fairly wet and a vehicle in front of me is kicking up a large amount of water/mist.
When the weather is dry- zero issues.

The mechanic pulled the info and it says that its having a high pressure fuel pump issue- or at least its saying it is, as the computer is thinking its not getting enough fuel/running lean, so its cutting power. We watched the left fuel rail pressure reading drop to .1 while driving it in some light rain. So it's cutting pressure to it for some reason. We then replaced the fuel rail sensor since its an electrical part- no change, still stutters in the rain. The mechanic does not think its the fuel pump on that left side since its runs off the cam and not anything electric per se- so doesn't seem to make sense water could cause that mechanical aspect to act faulty, would seem it would be the sensor? But that didnt fix it.

I put the Dinan tune into bypass mode and still misfires, so that has no effect so far.

Mechanic thinks its might be one of the car's two computers, which he cant do- he's an independent BMW mechanic.

Anyone have some insight they can share about what this might be?
I cant get my car into the dealer to take a look until two weeks from now anyway, even if I have to go there, as they are booked that far in advance.

Thank you.

[Tomcat_F15_STL]

You better check the rain gutters at the back of the engine compartment.

Make sure no plastic parts are poorly installed, broken or missing. A lot of people have suffered a lot of expensive damage from water dripping down on top of the intake and dme.

[DanHalen]

We just cleaned them out really well- and it ran great when dry, but again started to misfire when it began raining. But good to know- it's possible something isnt aligned right, etc. I will check again.

[Chilled]

Each bank is controlled by a separate DME. Double check all the lines/connectors. By the sounds of it, moisture is getting in somewhere.

[suitedcboy]

Look at fuel rail pressure sensor pins, take photo of pins in connector with phone and then manipulate/zoom in and look. Use a male terminal of correct size and check pin tension/pin drag. Verify the rubber seal is not missing or damaged on the connector. wetnes causing bleed over and wet connector with terminals that are loose can cause the pressure sensor to read wrong so that actual pressure may be much lower than what the sensor signal indicates to that DME module. I have had issues with wet engine performance on Bosch FI diesel engines and other brand gasoline DI engines. The sensors are near identical with the same connectors. More common on diesel since they have higher amplitude hgih frequency vibrations that wear electrical connections but gasoline do it too.

[RED_Y_]

Sounds like a corroded connector somewhere.