Don't let the smoke out!

coupesport said:
if so this should be rectified - and we could logically say that was the culprit...
you may not even have to replace your alternator but that AL41X has juice to spare
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Oh yes, without a root cause there is no point in declaring it fixed...
 
Thanks guys, current thinking is that the starter is shorted to ground and eating all the available amps, so the dash indicator lights don't even glow. I'll get the DMM on it and see what is revealed. I think: one meter pin to B+, the other to the block. There should be no voltage between the two. I have to think about this a bit.

Looking at the wiring diagram(s), there are several ground points throughout the car for various groups of electrical consumers, but where is the main ground for the engine?
 
First, disconnect the cable that goes to the starter and tape it up to make sure it isn't grounded. Then turn on the ignition and see if you get voltage on the other circuits and that the other things are working properly.
 
Honolulu said:
Thanks guys, current thinking is that the starter is shorted to ground and eating all the available amps, so the dash indicator lights don't even glow. I'll get the DMM on it and see what is revealed. I think: one meter pin to B+, the other to the block. There should be no voltage between the two. I have to think about this a bit.

Looking at the wiring diagram(s), there are several ground points throughout the car for various groups of electrical consumers, but where is the main ground for the engine?
Click to expand...
H> I think: one meter pin to B+, the other to the block. There should be no voltage between the two.

Disconnect the battery, measure ohms between B+ and the chassis ground. If you see zero ohms then there is a short.
Else, repeat with the key moved to RUN, if no short repeat with the key moved to START.

If the short is only during START, disconnect the starter positive, reconnect the battery, and push start the car. At 6 ft 6 I bet you can push start the car as a matter of course.

My battery has a braided copper ground from the battery (-) to the engine bay. There should be another braided copper ground from the chassis to engine/tranny I heard. These can carry the AMPs. The other grounds are toys.
 
Oh, I've push started many a car and my bikes as well. I live 800 feet up a ridge behind Diamond Head. OTOH if the car doesn't start, I'll have to bug my pal for his Tacoma and tow strap.

Now all that's lacking is the mental energy to actually perform the work.
 
Honolulu said:
Oh, I've push started many a car and my bikes as well. I live 800 feet up a ridge behind Diamond Head. OTOH if the car doesn't start, I'll have to bug my pal for his Tacoma and tow strap.
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Wow, it's a small world, I used to live on Poka St., one street up from Diamond Head Rd. That was a couple of years before I bought my E9 on Maui though.
 
Have we mentioned if this is an auto or standard? The auto has a relay for the starter.
 
Car is manual, converted from AT to 4-speed, then 5-speed. It worked when parked. I spent a considerable time figuring out the start sequence from the electrical diagrams and I *think* I took out all the wiring made extraneous by the trans swap(s). It ran for years in all three trans situations. Either I got lucky or did it right.. until. Something about the long layup has changed things.

In the face of an immediately upcoming 5-week trip to Munich, I've not gone in after the starter which is my current and only suspect after I verify some wiring and put on a substantial engine ground. R&R of the starter years ago wasn't any fun at all.
 
mulberryworks said:
Voltage is like water pressure in your pipes. It will try to find a path of least resistance, but if the only way is a high resistance path and there is enough voltage, the amperage can do some damage.

Decades ago I had a 1983 Mercedes 300SD with a 5 cylinder diesel. The starter was being intermittent and I was making sure the grounds were good. After taking off the ground straps from the starter and the engine, I decided to turn the key to start to see if my guess that nothing would happen was true. Nope. The starter wanted its juice and the only ground it could find was through the climate control. Smoke started pouring through the dash vents and didn't stop after I turned off the key. I leapt out of the car and unbolted the cable from the battery. So in addition to replacing the intermittent starter, I had to replace the entire climate control. Ouch.

There is no fuse in the starter circuit as it can normally handle the load. When the grounds are poor, the power will find a way to complete the circuit and that can result in things getting fried.
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Kinda sorta...

Voltage is like pressure in pipes, but unlike water, electricity only flows according to a very specific law called Ohm's Law. Here we have V=IR.

If you have a high voltage and a high resistance only a small current will flow. Electrons are not like water behind a dam that will try to make that path a lower resistance (like water would through erosion). They may try to find another path (for example an arc), but if the resistance is high in any circuit, the current will be correspondingly low, and clearly that is not the case here.

I think this issue is more complex than it seems. As @Arde noted, If the B+ wires are burned, then that is where the current was flowing. Now, it is important to rememberer that the B+ wire from the alternator comes directly from the alternator diodes. Current can normally only flow OUT of the alternator to the battery. The alternator itself does not generate any current unless it is spinning, so since the motor was not turning, the current causing the burning wires had to be coming from the battery (there is no other source of current in the car when the motor is not turning), and INTO the alternator (key observation).

If the only source of current is the battery, then the obvious question is, where is the ground that is allowing battery current to go INTO the alternator, and thence to ground?.. There are two possibilities:
1) One or more of the alternator diodes is shorted (somewhat unlikely, because they would more probably fail open)
2) The voltage regulator is shorted and the field coil is being energized without the alternator turning.

The #2 mode is a bit weird.. The BMW voltage regulator is a modular unit that directly senses the battery voltage (i.e., on the internal end of the B+ wire). This then opens or closes a switch that ties the ACC or RUN bus line to the field coil. As I recall the field coil wire is external to the alternator, and thus is not just the B+ line. Now, if the voltage regulator developed a short from the sensing wire (internal) to the field coil wire, then this would allow B+ current to flow from the battery into the regulator, and from there to ground through the field coil, which, when stationary, is pretty much a dead short to ground.... Normally this would not occur for three reasons: a) the regulator is not shorted, b) the unloader relay will disconnect the ACC bus from the circuit when the key is in the START position, and c) the alternator is moving so the reverse EMF in the field coil would not make it look like a dead short...But if the regulator is shorted, all bets are off.

In any case, it seems that the culprit is the alternator. Either shorted diodes or a shorted regulator. Fortunately the regulator can be removed in about 20 seconds, so do that and then carefully apply power to the battery. If nothing happens, then it is the regulator. If it still smokes, then it is the diodes.

Good Luck!!

Scott
 
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