1G Alternator going bad? At idle when the radiator fan kicks on the car dies

[boosted99_420]

Ok so i just got my 1990 TSi awd. It has a brand new motor in it HX35, 1350ccs, etc. etc. The volt meter i have in it says its reading 13.6 volts while driving but when i get to a stop light and the radiator fan kicks on the car dies. If the fan stays off the car is fine and idles like normal. What would be the cause of this? My guess is the Alt is going bad since it wasnt replaced with the new engine. Let me know what you guys think i dont have much personal time in the Army so any time i get is precious. Thanks in advance for the help guys.

 

[DSM1G90]

No, ALT is fine since the voltage is reading as it should.

Odd though that you would lose power to the ignition system when the fan comes on.... You got some serious current drawing accessories (like car audio sound booming junk) attached to the system, for when the relay closes to turn on the fan, there is a bit of current draw at the beginning.

How new (or old) is the battery along how tight and clean are the connectors?

If you got a bad battery (which eventually will blow an alternator anyway), then that would explain the reason of things dying since the battery is running the system and the ALT is just a regulator to the current draw from the battery.

 

[boosted99_420]

Battery is brand new I believe I will double check. No boom boom in the trunk has radio,boost,wideband,avrc, and a big ass tach thats got to go. Maybe the ISC is bad?

 

[cadilacmike]

It might not be the ALT, but I had a similar issue alternator tested fine, still would not charge the battery changed the alternator today and it fixed it. Might be worth a look anyway.

 

[boosted99_420]

The Alt is gone in it not charging at all at idle only at medium rpms.

 

[VisegripMech]

Could the fan itself be faulty? Or would that always blow a fuse? Does the same thing happen if you turn on the AC?

I don't think the alt normally charges at idle, it should show about 13.5 volts

 

[cadilacmike]

When i measure mine at the alternator, it's putting out 14 something. Now at the battery its 13.8-14.4, but it yea it should charge at idle.

 

[boosted99_420]

There is no ac in it. Also will be taking out power steering soon. While engine is cold it charges at 14.2 volts but once it warms up is when it dies. Batter shows 12.6 just enough to start it good.

 

[cadilacmike]

That's kind of what mine did except it would read 14 volts every once in a while sitting in the drive, go for a test drive come back out would be 12. Its worth a look, I went through 2 batteries, alt fuse, alt relay, and the second new alternator did the trick, I don't know much about the sensors and how they work.