Oh yes, without a root cause there is no point in declaring it fixed...
Don't let the smoke out!
- Thread starter Honolulu
- Start date
Honolulu
Well-Known Member
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?
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?
ElGrecko
Well-Known Member
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.
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.
Honolulu
Well-Known Member
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.
Now all that's lacking is the mental energy to actually perform the work.
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.
Honolulu
Well-Known Member
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.
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.
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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Honolulu
Well-Known Member
Thanks for those thoughts, Scott. Failure of the alternator would seem to be ruled out since O'Reilly got it to work on their tester.
Another thought: just how/where is the engine grounded to the body? Although I've not removed anything (lately) that would seem to have served the purpose of grounding the engine, somehow current is flowing where it shouldn't and I can't see a ground nor recall ever having seen one.
And another: how does one identify an internally regulated alternator? I have some vague recall of having, maybe, changed the alternator at some point.
Another thought: just how/where is the engine grounded to the body? Although I've not removed anything (lately) that would seem to have served the purpose of grounding the engine, somehow current is flowing where it shouldn't and I can't see a ground nor recall ever having seen one.
And another: how does one identify an internally regulated alternator? I have some vague recall of having, maybe, changed the alternator at some point.
restart
Well-Known Member
I think…. An old style alternator with an external regulator has a 3 wire plug, similar to a headlight plug.
A newer internal regulator alternator only has 2 wires.
I’m like ai though. Sometimes wrong.
A newer internal regulator alternator only has 2 wires.
I’m like ai though. Sometimes wrong.
Another thought: just how/where is the engine grounded to the body? Although I've not removed anything (lately) that would seem to have served the purpose of grounding the engine, somehow current is flowing where it shouldn't and I can't see a ground nor recall ever having seen one.
Braided cable at firewall to #6 cylinder area of engine. About 6” long.
When bad or disconnected your throttle linkage will get hot and spark at the throttle body as it becomes the engine ground
Braided cable at firewall to #6 cylinder area of engine. About 6” long.
When bad or disconnected your throttle linkage will get hot and spark at the throttle body as it becomes the engine ground
I think we go back to the question of the burned alternator wire. If that is the primary DC wire (and not the field wire) then, with the engine not turning, there is no reason that wire should conduct. It leads directly to a set of diodes all of which are blocking any current INTO the alternator. The engine was not turning, so the alternator was not generating any current, so somehow that wire is leading to a short, either inside the alternator, or some mechanical short to the alternator body and thence to ground.
I am not sure I'd necessarily trust some dude at O'Reilly to confirm the operation of the alternator either. The test they perform may not address the issue you are having.
Can you trace the burned wiring? Where did it start?
My guess, and you probably won't like this, is that you hooked up the jumper cables backwards. The ONLY source of current was your jumper battery, and the only way that current could go into the alternator (if it is somehow not internally shorted) is if the alternator diodes were forward biased. The only way that could happen is if the jumper battery was hooked up backwards.
Below is a typical alternator. You can see the three diodes (the arrow-like things) on the right. The terminal marked "Battery Terminal" is the wires you say are melted. Current can only flow in the direction of the diode arrows, which is to say it cannot flow INTO the alternator. If the battery was hooked up backwards then you can see that current would flow directly from ground through the diodes and back to the battery.
This is also supported by the fact that you say there were no dash lights or any thing in the car when you tried to start it with the jumper battery hooked up. There would not be because everything was powered backwards. I'd disconnect the alternator wires, tape them up and re-attach the jumper battery, being certain it is connected the right way, and try the starter... The car will run without the alternator (for a while), and that should tell you if there's any permanent damage (I'll bet your alternator got pretty hot, so it might be worth $300 to swap it out).
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