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  #1  
Old 20th July 2011
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Default ahh cwap - alternator in 81 turbo sedan quit near work

1 minute away from arriving at work at 1 am this morning the alternator in my 81 turbo sedan quit working. No noise of slipping belt, no smoke smell.

It was raining and I was a little bit late so I didn't have a look in the dark, but I'm hoping it's just due to the large amount of rain all the way in.

I've got spare alternators back at home, so I hope the problem is something easy to do a bodgy fix on as I've got a 1.5 hr drive to get there. 8-)

I immediately thought of a few possibilities - earth connection come loose, D+ wire broken off it's lug, or maybe a diode.

The charge light came on and wasn't on steady but sort of pulsating (slight but regular change of intensity).

The rain of last night has gone away and hopefully if it was due to excess water the heat of the engine once I stopped the car might have dried it out. I'll find out when I get back to the depot and sign off...

Craig.
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  #2  
Old 20th July 2011
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Jim Mesthene Jim Mesthene is offline
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Heavy rain can help worn Belts to slip.
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  #3  
Old 21st July 2011
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It's definitely the alternator - I had no choice but to drive home on battery power and including checking out another potential rental property on the way home (which gave me time to debug the problem more while I waited for the real estage agent to arrive) I got to within 500 m of where I live when the voltage got too low (I reckon about 8.5 volts) before the hall-effect ignition module gave up and the engine stalled trying to get up a short but steep bit of the off-road track.

So it's now my landcruiser to the rescue - both to charge the batt in the car a bit and get the rest of my stuff out of it!

Don't have a spare battery up here so I'll need to jump-start off the landcruiser once it's charged a bit and drive it further up to the house.

At least I have two days off coming up after tomorrow so I know what I'll be doing to the car! lol

By the way the charging light was flickering and going a little dimmer when the engine was revving while driving, I'm thinking one of the diodes has gone. All the wiring at the back of the alternator is fine, ground connections are fine (I did continuity tests to be certain), and the belt is not slipping. Vreg is a new one I put in a few weeks ago so the brushes are not worn.

Craig.


Craig.

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Old 22nd July 2011
16saabs 16saabs is offline
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probably the brushes failing after all this time with it flickering, normally if the regulator goes on the back they go end of story, replace the alt and expect prob solved then get the old one repaired.
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  #5  
Old 22nd July 2011
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Quote:
Originally Posted by 16saabs View Post
probably the brushes failing after all this time with it flickering, normally if the regulator goes on the back they go end of story, replace the alt and expect prob solved then get the old one repaired.
I have both a rebuilt 70A and a new 80A alternator here. The 80A was one installed in my 89 900i for a short time before I fitted a 115A alternator to that car (it went when the car was wrecked in Feb). I got the 70A one a few years ago when I still had my white 83 900S and it looked like needing a new alt before I decided to sell the car.

I'm going to install the 80A one since the mounting bracket for that one (got a new one of those) is different to the mounting bracket for the earlier 70A ones in a way that gives the mounting bushes better support so less likelihood to 'bounce' as the bushes age. THe tensioner setup is also a little different with a longer bolt, so adds a little more stability to the setup.

The 80A one has different connections for the main output (M8 stud instead of M6) and the D+ connection (small M5 stud instead of a 6.4 mm spade lug) but I have some terminal blocks and wiring already put aside to link the current wiring to the 80A alt.

When I'm at it I will renew the ground connection from the alt to the engine block as well. Current one is fine but it links to one of the alt brackets bolts which is difficult to access if it breaks.

In the re 89 900i I reworked the ground connection to go from the alternator casing to a bolt on the fuel rail. With the 8V engine I will use a bolt on the head (maybe one of the intake manifold bolts) or directly on the block somewhere.

Craig.
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  #6  
Old 23rd July 2011
Geoff Weeks Geoff Weeks is offline
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Things that cause the alt light to come on are: Stator voltage much higher then battery voltage or the reverse. One or even two bad diodes will not likely cause the light to light. A fried regulator could. The dimming at higher RPM's could be because of residual magnetism in the rotor, the stator voltage is riseing a bit, say to 3-4 volts but not enough to turn the light out. If the pulley is turning, the wires are connected, I would 1st suspect the voltage regulator, regardless of how old it is. Brushes and/or sliprings are a possablility as is a shorted stator, but these are less likely.
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  #7  
Old 23rd July 2011
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Quote:
Originally Posted by c900 View Post

In the re 89 900i I reworked the ground connection to go from the alternator casing to a bolt on the fuel rail.
Undo that.
It's unwise to run the Alternator's full output through the Fuel Rail, even peripherally.
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