Weird Electric issue on an Audi

[Jay-ZS+]

Just done a fair bit of work on a mates audi. He asked if Id lend a hand with a service, sure I though, oil and filter change. Didnt realise he had a major service in mind! So weve done the cambelt, clutch, tappets, sump gasket and crank seal to name a few bits! Ended up getting a crane and taking the engine and gearbox out as it seemed like it would be easier.

Anyway all thats done and engines back in but go to connect the battery and get lots of sparks and some smoke! :yikes: Guessed it was a short.

Checked the wires to the starter and alternator and they are fine. IIRC there is an Earth from the -ve battery to body. Starter to Chasis. There doesnt seem to be one on the gearbox although cant remember taking one off.

Whats the weirdest thing is the battery measures 12v when disconnected. After a few attempts we manned up and just connected the battery, the car was totally dead, measure the battery whilst connected and its 0.06V then disconnect the -ve terminal and its measures about 2V and gradually grows until it reached about 10.8V after 45mins or so.

Guessed there is something drawing the current out so pulled all the relays one my one and still sparked.

Most of the work seemed to be down in the rain, so now im thinking there is water in the alternator. Anyway its baffled me! So Im asking of ideas :)

[peterzs]

Remember working on one of my cars and hit the terminal on the alternator, big flash and I killed it.

Something to do with the diodes, if you reverse the charge it kills them.

Have you tried disconnecting the alternator and seeing what happens to the charge.

Would worry me if there is that much of a short, starter motor connected up right???

Sounds like a lot of work going on there Jay, might be worth getting an auto electrician out. So easy to burn the loom or starter/alternator, and if its an Audi, dont expect replacements are cheap.

[Jay-ZS+]

Yer we disconnected both the starter and alternator one at a time and tried connecting the battery. One stange thing is that if something is pulling a charge you would have thought there could be a current between the -ve terminal and the -ve earth whilst disconnected, although there isn't.

Battery hasn't reversed polarity. Tried hooking up my battey and it was like bonfire night, with a shower of sparks when we went to earth on to the engine block. If it was me I'd prob get someone to look at it although my mate is on a major budget. So wants us to try everything first see if we can get to the bottom of it.

[zsserbia]

Since the battery is completely dead, I'd look for a short circuit somewhere between a very thick wire with positive charge and earth, possibly direct contact with metal of the engine/chassis. Common sense tells me any thin wire would perish/burst into flame way before completely discharging the battery. Also, short is in an area not protected by fuses.

No offense, but I'd even consider that one of you guys may have bolted the main cable of positive charge somewhere to the engine/chassis. Otherwise, you should be able to tell if there is a spark/smoke somewhere other than just battery terminal.

Did the main + cable get very hot when you first connected the battery? How strong was the spark from the terminal when you first connected the battery (little spark is normal)? If it was strong enough to melt a chunk of battery terminal I bet it's the main cable.

Use extreme caution on this one as battery may even explode/cause fire somewhere in the circuit.

Try to disconnect the main cable to the starter motor and and carefully connect a good battery to see what happens... If still no go, try with the alternator.

Good luck!

[Jay-ZS+]

Assumed it would be one of the big 3 wires. Will check the wiring to the starter again, as my mate did the wiring whilst I dropped the crane back but it seemed good. The spark was as if it was arc welding to the terminal defiantly more than the standard spark!! Will have a look over it again and trace all the wires back.

[peterzs]

Wonder if the missing earth cable to the gearbox has been bolted on to the starter motor???

Best of luck Jay, just take care as it sounds like it could all go bang!!!!

[talkingcars]

Definatly needs to be some sort of earth lead from the engine or gear box to the body or battery, it is the only way the power returns as the engine and all it's connections are insulated in some way.

Connecting the 2 terminals of the battery give some big sparks, there is enough ampage in a car battery to arc weld to a fashion.

This suggests that somewhere a battery lead is wired wrong to give you the fireworks.

[Supercharged_Z]

when you find it, it will be one of them moments where you slap your head and cannot understand how you missed it lol.

It can probably only be one of a few earth cables/ positive cables to give such a spark.

[Enright]

Seems a bit strange to have big thick earth from the starter motor - it's normally earthed through it's own casing by being bolted to the gearbox, and then relies on the gearbox earth to chassis.