2002 Beetle 2.0L electrical surging and frying parts

[jwups0887]

I build motorcycles and kit cars as a hobby, but this beetle is stumping me right now.

This year the car battery died, I charged the battery and tested the alternator and found the alternator needed replacing and haven't had a problem with the current battery which is still pretty new looking.

The car died on my daughter one night and had to have it towed home so I could fix it, further inspection revealed the ignition coil was fried, it totally melted down one of the metal pins. So I installed a new one six months ago.

My daughter went to NY and it died again. The mechanic at the garage took a week working on it to try and figure it out. He said it needed a new alternator wiring harness and a fuse box, but he didn't really sound like he knew since everytime I talked to him he wasn't sure.

Well the fuse box he put in has melted down, I used house electrical wiring to make the needed metal connections so the car could run. So what ever he thought would fix the problem turns out it didn't.

Current state:

I tested the battery at rest it is a 12.55 volts, it had been started the previous night.

The new alternator had the voltage regulator already attached when I installed it. I tested it with the car at idle and the charging ranged from 14.5-14.9 volts. I had my daughter bring the rpm's up to 4,500 to see if for some reason the voltage regulator was bad, but it topped out at 14.12 volts and never went any higher.

The cylinder 3 was misfiring, which I was betting it was the ignition coil again, when taking off the ignition coil I found #3 was fried.

So far the battery fuse box is fried, the ignition coil is fried, #3 plug wire is pretty fried.

I also don't want to replace anything more until it is figured out what is causing the problem.

Is there anything else in the VW electrical system that could be surging, something that I am overlooking?? Right now nobody can figure it out and with my knowledge I should be able to.

Has anyone had any problems with electrical surging?

I really don't want to just start buying parts just because it is part of the electrical charging system and do a round robin of parts.

I appreciate anyone if they have any idea, Thanks.

[MyOtherRidesAVette]

The first thought would be the voltage regulator. I believe the proper rpm to laod test is 2000, but regardless, it sounds as if you have that under control.

As to the battery box, yes these are problematic, typically, not always, but typically, caused by the black lead from the alternator at the attachment point on the fuse block. It is a concensus of opinion that this is because of low quality wiring used. A good insight into this problem is found here -
MORAV needs some help helping someone else on the Org! - Battery Fuse Box Issue

It sounds as if you have enough knowledge to do voltage drop testing of the cable(s) involed, but that said -

Voltage Drop Test
Voltage Drop Testing

Alternator Voltage Drop Testing (excellent)
Alternator Voltage Drop Test

Alternator Amperage Output Testing
Alternator & Charging System Checks (Alternator Testing)


I haven't read where anyone who has replaced this particular cable has had continued problems. Several, however, who had replaced the fuse box multiple times until replacing the cable(s).

As to the coil issue, I haven't a clue (no DTCs?), but I can put up the wiring diagram(s) if you'd like.

MORAV

[jwups0887]

Thanks MORAV,
I have done the voltage drop test and also did the alternator amperage output test, the one I didn't do was the alternator voltage drop test which I will do.

In the battery box the one that keeps melting down and it also melted down 6 months ago was the coolant fan, 2 speed. Would that point to maybe a fan relay, some other sensor or maybe the fan itself resulting in it melting down? Right now I have 10 ga house wire connecting it.

If I was to replace all the wiring to the battery box with a real heavy guage wire bought from home depot, do you think that would solve issues with battery box or the surges which cause things to melt down?

Yes you are correct, no DTC's.

Thanks, JR

[MyOtherRidesAVette]

I'm going to go look at the Bentley and see what size wire is there now. So we are clear, this is the 3rd connection from the left, the FCM (S164) 40A fuse.

I would say right off, as a guideline, since "in wall" house wiring is 15A and 12 ga. is used, and commercial wiring is 20A and 10 ga. is used (and they are both solid as opposed to strand), and god forbid, your talking about 14ga lamp cord wire, what you are using is far too light for a 40A circuit.

Give me a little bit and I'll be back with more information and some thoughts.

Edit:

The cable running from fuse (S164) directly to the FCM is a 6.0 mm², slightly larger than a 9 AWG wire. A 10 AWG would be smaller, so a rewire should be a 8 AWG stranded. I am the first to admit, I know little about VAG testing, but have read enough in the Bentley Repair Manual (DVD-ROM) not the paper Service Manual, to know that many, many components can be read and checked with VAG equipment, by a knowledgeable user, who also knows where to go to get the applicable values. Now, that sad, if you are experiencing no problems with the auxillary fans and everything is working as it should, it is doubtful there is a problem with the FCM. More, that as with the Alternator cable, this may just be an inferior grade wire, although overheating of a wire is usually associated with an overload or a bad/dirty/loose connection. I can't stress enough, that if you are going to make up your own cable, you use a proper crimping tool as often problems are created with adequate contact surface within the solderless connector, creating resistance, and defeating the size wire being used. There is a link in this thread, for the correct testing of the auxillary fan system components, sans the FCM.

Bentley Cooling System Diagnostics
Overheating problem

I have serious doubts that your coil issue is related to this issue. Again, that issue may best be left to VAG diagnostics.

Sorry I can't offer more.


M.

[jwups0887]

Yes you are correct it is the 3rd from the left. S164.

I used commercial 10 gauge solid copper wiring, Now I know after seeing the diagram in the link you posted it is 40A.

Also I've unhooked the secondary air injection pump to get to the ignition coil, do you see it being a problem to start it up with out to do the alternator voltage drop test?

Thanks, JR

[MyOtherRidesAVette]

I've added to my post above since you posted the last response. And to answer your question, I can't answer your question, just don't have the knowledge in that regard.

M.