Technical Most likely misfire during heavy rain

[MonkeyPotatoes]

Partner’s car is acting up again.
Fiat 500, 1.2L, Pop, 2016.
Seems to only start misfiring during heavy rain, and then followed by a Christmas tree of lights. Haven’t been able to stick an OBD scanner on the car as it happens once in a while.

Seems to idle stable, when the dash lights haven’t come on yet. Very limited in detail at the moment, until it happens again!

Have previously changed the EVAP solenoid valve, breather hose, map sensor, brake light switch.

Does anyone know a list of most likely issues that could cause this?

Sorry for the lack of detail, not sure what else to include - this car keeps visiting the garage every 2 months…

Thank you in advance.

 

[puntodeltathema]

Check the "duckbill" drains under the scuttle (have you got a lake where the wiper mechanism sits? May be running into the engine bay fusebox perhaps).

Also the heater drain to the left of the clutch pedal (remove footrest trim). Water collecting in the heater box will drip onto the ABS ECU, though that wouldn't necessarily cause a misfire. Over time would nuke the ECU and throw up ABS, ESP, fuel cutoff error messages on the instrument panel though (if they feature).

 

[MonkeyPotatoes]

Check the "duckbill" drains under the scuttle (have you got a lake where the wiper mechanism sits? May be running into the engine bay fusebox perhaps).

Also the heater drain to the left of the clutch pedal (remove footrest trim). Water collecting in the heater box will drip onto the ABS ECU, though that wouldn't necessarily cause a misfire. Over time would nuke the ECU and throw up ABS, ESP, fuel cutoff error messages on the instrument panel though (if they feature).

Thank you for this! This sounds worryingly correct but would need to have a look once we get a chance.

It’s been going on for over a year, thought it was fixed by replacing some of the other said parts…but here we are again!

 

[chris3234]

Plug leads? Would be easy to short out. A it when the engines soaked from road spray

 

[MonkeyPotatoes]

Plug leads? Would be easy to short out. A it when the engines soaked from road spray

Was thinking this too, along with spark plugs and coil pack (and HT leads as you said). I think this is the first avenue to explore if we go down parts roulette by the looks of it!