High mileage Gti major electrical problems in the wet

[Boy'dup]

Have had a worsening problem recently that seems to occur specifically when it rains; which is obviously all the time at the moment. It started throwing the EPC light with no conclusive error codes once cleared it ran fine again, then the occasional limp mode codes related to the throttle position sensor and barometric pressure in the intake manifold although these test and work fully. On the way home thursday it unusually started fine (usually if its wet it wont start, can be forced to start but will only run in limp mode) but by half way home all the ancillary electrics packed up and I only just made it back, it literally threw every warning light and buzzer imaginable like when the alternator goes. I am really frustrated with this now its been going on too long. leave it in the dry for a day and its fine till the next heavy rain.

The cars an AVY on 165k miles

I need to mention this seems to be the wettest car on earth, when i picked it up the channels were blocked and everything was sat in water, I've drained the rear lights which were like fishtanks and drilled some holes in the bottoms, cleaned all the electrics. I've been round the whole car cleaning and waterproofing all the connections, got allsorts of rubber matting etc covering the ECU. Its recently had a battery, alternator, leads, plugs, oil, crank sensor and probably a few more bits I cant remember. The only thing left is the spoiler brake light which now has condensation on the inside but surely that wouldnt cause non starting? Going to try to dry and seal that light tomorrow and see what happens. Really starting to annoy me now, we have 3 lupo's and none can be driven (emma's is awaiting a new gearbox). This is a mega pain and I really need to sort it quickly, any help would be appreciated.

Also to add the cars been perfect until this, full vw history regular servicing and 95% motorway miles, it drives spot on and the engine runs really smooth and doesn't drink any oil. Passed an MOT on wednesday needed 2 tyres

thanks in advance

Edited July 13, 2012 by Boy'dup

[Defcon5]

Does it have the undertray on?

Water getting in the alternator maybe?

[Lupopo]

Check that your ECU isn't gettin water ingressing into it, it's located behind the scuttle panel. Hope that helps

[Boy'dup]

Undertrays off because i'm always under it, possibility but the problem was occuring originally with the tray on. The batterys not going flat either but I'll not rule that out will check the output on it tomorrow and get the tray back on, then everything should be waterproof. Havent checked the lambda either, the car had water sat in the exhaust. I cant explain how much I hate limp mode now. Has anyone else experienced any water related problems? other than this the cars in a great bill of health and on dry days its cracking, Got some bits to do tomorrow will report back when I've tried them, trouble is I wont know until the next downpour whether its sorted or not. Lupopo the scuttle was sat in water and leaves etc when i bought the car, have cleaned the channels etc, The plugs on the ECU didn't look too bad but had a blast of electrical cleaner and some silicone spray to seal after refitting, I have ensured that no water can now reach the ECU with rubber matting (its all a bit ghetto but I'm getting desperate). I guess theres a possibility that the damage has already been done? but I guess theres no real test for that either...

thanks all

[Boy'dup]

Fitted a new bosch alternator tonight after work, has sorted the charging issues. Proper diagnosis has led to the throttle potentiometer being faulty, is got a brand new tb and wiring on it, according the vw mechanic who worked on the car for 150,000 miles its actually happened before and was replaced by a second hand part. So i'll have to take the column and pedal box out swap the switch (also check for leaks in the bulkhead; there must be a reason its only happening on wet days) have a bonus in that the pedal box has been drilled out before and is now fitted with some normal 13mm bolts which will save on the work. Ideally need to find a part number for the switch before I do the work but cant get to it without dismantling the car, might pop up the scrappy tomorrow and have a look at some other vw's to see if they use the same switch.