Engine losing power in rain, c270cdi. w203.

[Deuchars25]

Can someone please explain why my partners c270 seems to be missing and losing power when it rains. Its only when it rains, the engine stutters and the car slows down. This problem has only been happening since we had a new inlet manifold put on earlier in the year. Also sometimes when it's raining, the dash flashes red and the low oil level warning is on. We've done the oil check's many times when dry and the dash say's oil level is ok. I took it back to the garage but they can't find anything wrong. Has anyone had a similar problem or knows what the cause maybe? I've listed this under electronics, because I feel like it is an electrical problem.

 

[alibally]

Is the fuse box lid on properly? Water car run in straight on top of the engine ecu and front Sam unit.

 

[camerontyler]

Hi Deuchars25,

I've had this twice since i've had my w203, although not the power problem, not that i've noticed anyway, but i've had the light come up telling me there's something up with the battery/alternator.
It has only happened when i've had no choice but to plow (slowly) through massive puddles during torrential downpours. Both times I have been taking it very easy and staying off the turbo due to the conditions which would explain not noticing any power issues.
I quivered for the next few miles expecting a nuclear meltdown, holding back the tears but nothing untoward happened.
I can only imagine water has touched the battery leads, or as Alibally suggested got in about the fuse box.

The second time was actually today thanks to the tail end of hurricane Irene we're getting hammered with at the moment.
I've used the car all day with a few stop-starts and not had any other issues. I imagine the water quickly evaporated off.
The car has also just been serviced with a full check-over by the best indies in Scotland and they didn't find any faults.

To conclude, don't worry too much about it, just check your fuse box as Alibally said.