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Author Topic: Diesel Alternator / W output  (Read 4958 times)

January 21, 2009, 11:48:40 am

Stoop

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Diesel Alternator / W output
« on: January 21, 2009, 11:48:40 am »
Having some troubles with my tach / W output.
When I start the car, the alt light stays on, and the tach reads 0, or very little, until I rev the vehicle up to over (almost exactly) 1700 RPM.

At this point, the light goes out, and the tach works fine.

I have had 2 or 3 alternators in this, and they have all done the same thing.

Is this a common problem?  Is there a simple fix?
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Reply #1January 21, 2009, 11:49:43 am

Stoop

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Dur
« Reply #1 on: January 21, 2009, 11:49:43 am »
Its a 87VW Jetta TD.
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Reply #2January 21, 2009, 12:10:30 pm

Vincent Waldon

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Diesel Alternator / W output
« Reply #2 on: January 21, 2009, 12:10:30 pm »
This is completely normal actually... it's even mentioned in many of the early Owner's manuals. ("If the alternator light stays on (except after an initial rev of the engine) consult blah blah blah")

The alternator needs to get to a specific RPM in order to "self-excite" and begin generating electricity on its own.

Because it's not generating electricity before this happens there's no tach output either.

I've had MK1s and MK2s that require that first initial rev,  and some that don't, and I now have one that used to not require it but now does... same alternator... go figure.
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Vince

Edmonton, Alberta, Canada
2001 silver TDI Jetta Malone Stage 1.5 , 2001 blue TDI Jetta SBIII 216s Malone Stage 3, 1970 Bay Window bus

Gone but not forgotten: 1969/1971 Beetles, 1969/1974 Westies, 1979 Rabbit, 1986 TD Jetta, 1992 gas Jetta, 1994 TD Jetta
Reply #3January 21, 2009, 02:36:13 pm

Smokey Eddy

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Diesel Alternator / W output
« Reply #3 on: January 21, 2009, 02:36:13 pm »
That's useful to know!
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Ed
Blacked out mk2 AAZ Jetta RIP. You are missed.
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Reply #4January 22, 2009, 05:54:51 pm

Stoop

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Diesel Alternator / W output
« Reply #4 on: January 22, 2009, 05:54:51 pm »
crap,
So, maybe thats why my Autostart TGEN-100 isn't sending a signal to the compustar unit.

Gah.. I am about to snip the green wire!
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Reply #5January 22, 2009, 08:08:47 pm

jtanguay

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Diesel Alternator / W output
« Reply #5 on: January 22, 2009, 08:08:47 pm »
apparently theres some mod that will eliminate this problem.  one cold morning i went to start my car, then came back in.  go out and WTF car is shut off???  yea... forgot to blip the throttle... battery was DEAD   :lol: this was a while back though.

whatever 'mod' it is, its built into the new serpentine alternators.  it's been discussed on this site a while ago... i'll try searching for it.

here is the link to the alternator fix.  apparently its a voltage regulator?

and here is an example of one on ebay.  not sure if this will work or not though...  i couldn't see why not?
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Reply #6January 22, 2009, 09:52:31 pm

AudiVWguy

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Diesel Alternator / W output
« Reply #6 on: January 22, 2009, 09:52:31 pm »
I searched Voltage Regulator Bosch on fleabay. Found this Item number: 230320631404
I think I'll try one.  8)
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