[HugoCountsto7]

Originally Posted by maxoutput

Might also be worth checking out the B+ cable behind the fuse box as they are known to come loose and either cause gremlins, the car to shut down or turn the cars dash into a Christmas tree. Have you checked the wires from a alternator plug for continuity leaks between them ?

I have not checked the connection at the fuse panel, though I've heard this is a weak spot. How do I gain access to this terminal? Is this a full dash removal? (edit: will look into this: http://www.bimmerforums.co.uk/forum/...guide-t461658/)

Could you detail how to check for continuity leaks at the alternator?

[HugoCountsto7]

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[PhaseP]

When car is running no current is flowing on that, so I doubt it is your problem.
The replacement alternator maybe faulty also, if it is remanufactured it happens.
One thing to try that comes to my mind, after engine set to cool down fully, start the car and get a hair drier or similar and heat up the alternator with the hot air. And monitor if you get the problem this way before engine warms up. If it does, it is the alternator.

[smallseafishie]

I'd check the water pump. Initiate the water pump bleeding procedure with the vehicle off and see it it induces large unexpected swings on your electrical load.

[HugoCountsto7]

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[HugoCountsto7]

Originally Posted by PhaseP

When car is running no current is flowing on that, so I doubt it is your problem.
The replacement alternator maybe faulty also, if it is remanufactured it happens.
One thing to try that comes to my mind, after engine set to cool down fully, start the car and get a hair drier or similar and heat up the alternator with the hot air. And monitor if you get the problem this way before engine warms up. If it does, it is the alternator.

The new alternator is new (not rebuilt, not refurbished). I don't believe the alternator is the problem, but I will definitely make efforts to cross it off the list. I'm on board with your way of problem solving...its often much easier to aggravate the problem. So, what do you think I should concentrate on heating > the alternator body or just the voltage regulator?

[HugoCountsto7]

Originally Posted by smallseafishie

I'd check the water pump. Initiate the water pump bleeding procedure with the vehicle off and see it it induces large unexpected swings on your electrical load.

I pushed some thin test probes into the connector plug which should be plugged into the Aux water pump. If the AC is running or nothing is running I was measuring 13.3 volts. When the Heat is switched on I measure 14.1 volts. I'm not sure I understand this. Does this pump run on 14 volts? Why would it be getting 13 V when it should be off?

The electrical event never happened during this and the alternator voltage did not move when heat was on or off.

[galahad05]

Originally Posted by DLoBrown

I have not checked the connection at the fuse panel, though I've heard this is a weak spot. How do I gain access to this terminal? Is this a full dash removal? (edit: will look into this: http://www.bimmerforums.co.uk/forum/...guide-t461658/)

Could you detail how to check for continuity leaks at the alternator?

Sorry to butt in: my guess is max was speaking (regarding the alternator continuity leaks) about the impedance between the lines.

Here, let me post the other alternator pages (note, this is from my Bentley for the 2006-2011 (I think 2011) e90/91/92/93.

[galahad05]

[maxoutput]

Originally Posted by DLoBrown

I have not checked the connection at the fuse panel, though I've heard this is a weak spot. How do I gain access to this terminal? Is this a full dash removal? (edit: will look into this: http://www.bimmerforums.co.uk/forum/...guide-t461658/)

Could you detail how to check for continuity leaks at the alternator?

Just do a simple probe on the plug terminals just to check that there is no continuity between the cables, just on the off chance that the cables are split at any point and touching each other

The B+ cable enters the back of the fuse box , you can feel it if you reach up the back but you may have to drop the fuse box to check it. Whilst I'm not saying this is the issue it can cause a miriad of electrical issues if loose and arcing when it gets hot due to resistance.

[HugoCountsto7]

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[HugoCountsto7]

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[PhaseP]

When you measured car running the current flowing throws off the measurement. In other words you cannot measure resistance on live circuit with current flowing.

I know you don't suspect this because you have a new alternator, but the symptoms are pointing to a bad alternator.

[HugoCountsto7]

Originally Posted by PhaseP

I know you don't suspect this because you have a new alternator, but the symptoms are pointing to a bad alternator.

What are the chances that both the old and the new alternator exhibit the exact same failure mode only when heat builds in the engine bay? The old alternator did the exact same thing. I know all experience points to the alternator, but observation says some other issue was/is common to both alternators.

[galahad05]

Without it being the alternator, still feels like a huge load spike or bad wiring.
More like the latter. Seriously, an intermittent ground or + voltage line connection will definitely cause the alternator to go crazy on it's charging voltage.
And an intermittent contact or frayed wiring insulator would totally match up with it going bad (sometimes) with a warmed up engine bay.

[galahad05]

Or, more generally, I should say, ANY of the alternator wiring. +, gnd, or control lines.

The crazy spikes are a classic symptom of either a bad alternator or bad wiring harness to the alternator.

[galahad05]

Here's an example of something similar to what you're seeing, but with an older model corvette.

https://www.corvetteforum.com/forums...uses-them.html


Come to that, I seem to vaguely recall having something like this back on my old '68 corvette......though that car had so many problems in so many areas over the years I can't keep them all straight in my head.

[HugoCountsto7]

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[HugoCountsto7]

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[galahad05]

Not the dealership, no. Someone (an independent shop) that the local BMW community really recommends. A shop known for being able to track down and diagnose intermittent problems.


You'll be chasing electrical gremlins all over the car. The Dealership's typical method is, "try method A (replace part), did it work? No? Try method B (update software), did it work? No? Try method C (replace another part), did it work? No? Try method .....".

Eventually, assuming your bank account is big enough, they'll have solved your issue.




Side Note: Some dealerships have a warranty on their repairs.

[galahad05]

What is your ground strap made of? Did water/other contaminants get in and erode the electrical conductivity of your strap?

[HugoCountsto7]

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