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Sunnyside

996Tt Alternator

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Hi all,

Could anybody describe what the symptoms are of alternator failure. I dont have a warning light but the voltage output is down to 11 volts.

Is this the alternator? How many of you out there have had this problem.

Any advise /info greatly appreciated.

Frank

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Yep, alternator. Mine happened all of a sudden, low voltage but had a battery/generator cel. Made horrendous noise when reving motor, good news is you can get a bosch remanufactured for a fraction of the price of new with near same reliability.

Cant really complain, mine lasted 10 years.

Hi all,

Could anybody describe what the symptoms are of alternator failure. I dont have a warning light but the voltage output is down to 11 volts.

Is this the alternator? How many of you out there have had this problem.

Any advise /info greatly appreciated.

Frank

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unplug the battery when the engine is running. if the engine dies, the alternator is bad. if the car still runs, the alternator is fine.

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unplug the battery when the engine is running. if the engine dies, the alternator is bad. if the car still runs, the alternator is fine.

You are kidding, right? At least I hope you are kidding.......................

Edited by JFP in PA

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unplug the battery when the engine is running. if the engine dies, the alternator is bad. if the car still runs, the alternator is fine.

DO NOT DO THIS!

- Never disconnect battery with engine running.

- Never start engine without securely connected battery.

- Never use a boost charger to start the engine.

Disconnecting the battery will subject the voltage regulator (and computer and audio equipment...) to significant voltage spikes which may cause an otherwise good alternator to fail. Even if there were no damaging spikes, this test would not indicate whether or not the alternator was good because the engine will easily run with a weak or failing alternator.

Simple Test:

If you want to see if your alternator is producing current, turn on your headlights when you're parked and the engine idling with the headlights shining on a wall (at night). Notice how bright they are. Then turn the engine off. The lights should get dimmer when you turn the engine off. If the lights get brighter when you kill the engine, the alternator was not charging sufficiently. When doing this test, the lights should be the only load (turn the stereo, a/c and other accessories off). With a heavy load, an otherwise good alternator may not be able to produce sufficient amounts of current at idle.

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Thanks for the advice.

This morning I started the car and it was about 13volts by the time I had driven 5 miles it was down to about 11.5 :cursing: :confused:

There must be some juice as when I put everything that can be put on the voltage drops when the iggnition is off but will not go over 11.5 volts no matter what..... :(

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Hi again Frank!

It is usually the diode pack which fails in the alternator. It is a Bosch part (Part No. F 00M 145 350) and they are about £20-25.

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I had the same issue with my 996 (non turbo) and after replacing 2 batteries, the alternator, and the starter. And guess what? The exact same problem was still there.

Not sure how the 996tt is configured, but I ended up having to replace the ground strap from the engine to the body AND the badly CORRODED power cable (source of problem) from the starter to alternator to battery lead.

If the car is old and has had engine washed, stored in a damp climate, stored outside, etc. there is a chance it could be a corroded cable.

A bench test on the alternator done for free by most auto parts store will confirm whether it is good or bad.

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I had the same issue with my 996 (non turbo) and after replacing 2 batteries, the alternator, and the starter. And guess what? The exact same problem was still there.

Not sure how the 996tt is configured, but I ended up having to replace the ground strap from the engine to the body AND the badly CORRODED power cable (source of problem) from the starter to alternator to battery lead.

If the car is old and has had engine washed, stored in a damp climate, stored outside, etc. there is a chance it could be a corroded cable.

A bench test on the alternator done for free by most auto parts store will confirm whether it is good or bad.

That is something really interesting. Thanks for sharing!

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I don't think it applies to me... my engine bay, including all wiring is brand spaking new... :( I saw it...

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Engine not running: I have measured from the positive connector post next to the alternator to the engine, chassis and using jumpers to the neg terminal of the battery and compared it to the pos /neg terminal on the battery and only 0.4 volt difference. There is one lead from that post going to the alternator another to the starter and rest of car and a thinner one as yet I have no idea where it leads too. But if there was corrosion on any connector up to the starter , with the current it requires I would have thought I would have starting issues.If there was a connector lead problem from the starter to the post I would have thought the battery voltage would differ from the post voltage. So the only lead/cable not checked is the one to the alternator.

Engine running: Post voltage is 0.4 volts more than voltage measured at the battery. 11.4 and 11.0 . So either the alternator isn't pushing out the full 12v or the connector form the post to the alternator is duff.

From what I can see it doesn't look too bad but viz is not that good. So it will have to be alternator off.

Also using jumpers checked earth continuity to engine/chassis and battery all ok :(

If it is the diode pack alls well and good but who knows.

Edited by Sunnyside

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Hi all.

Final update. It was the alternator. Voltage rectifier duff. Porsche replace alternator under Warranty Wise. Cost £1170.00.

Thanks to all that have replied.

:thankyou:

Edited by Sunnyside

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To piggyback on this thread, I had a suddenly dead battery last week. I bought a new replacement, installed it and noticed the voltage needle was dropping slowly immediately upon starting the car. Put a volt meter on it and confirmed it was losing juice, down below 12V before I shut it down. After some discussion on another forum I decided it was probably the alternator. I ordered one online and took the old one out this weekend. I took it to an auto parts store to have it tested and it passed. There was another thread that suggested it might be the clutch pulley, which might initially work but fail when the unit heats up, but my battery is losing juice when just started.

What should I check into next?

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To piggyback on this thread, I had a suddenly dead battery last week. I bought a new replacement, installed it and noticed the voltage needle was dropping slowly immediately upon starting the car. Put a volt meter on it and confirmed it was losing juice, down below 12V before I shut it down. After some discussion on another forum I decided it was probably the alternator. I ordered one online and took the old one out this weekend. I took it to an auto parts store to have it tested and it passed. There was another thread that suggested it might be the clutch pulley, which might initially work but fail when the unit heats up, but my battery is losing juice when just started.

What should I check into next?

Hi mate,

Trust me on this, I am an Electrician and it took me ages to work it out. I had the AA out who put a tester on and it was found to be ok. The alternator will work fine on start up but when it heats up it will start to slowly fail. Taking it off and putting it on a test bench will show nothing as the alternator has to get hot as the engine warms.

It is most likely the diode pack . Thats the classic symptom .

Frank

Edited by Sunnyside

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I replaced the alternator and now everything is fine. Now I have a non working alternator in my garage that I wouldn't mind bringing back to life.. How do you determine if the diode pack has failed?

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I replaced the alternator and now everything is fine. Now I have a non working alternator in my garage that I wouldn't mind bringing back to life.. How do you determine if the diode pack has failed?

Just replace it. It cost only $41.00 and you already got the DIY on Pelican tech forum. After you got yourself a spare alternator.... Part# F 00M 145 350

Just found out you can get this part for as low as $13.85 ?????

Edited by jpflip

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I replaced the alternator and now everything is fine. Now I have a non working alternator in my garage that I wouldn't mind bringing back to life.. How do you determine if the diode pack has failed?

As JP says, just change it and you will have a good alternator again. Always good for a spare. I didn't keep mine as there was a surcharge on the new one which I got back when I returned the old one.

Frank

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OK. i read the tread and am still struggling. I have this problem ... had the alternator tested at Advanced Auto ... they said it is putting out low voltage and needs to be replaced .... can i just replace the diode pack OR do i need to replace the alternator?

Also, i am having trouble figuring out what the appropriate part number is for the diode back .... FOOM-145-225 from the pelican parts forum does not seam to be a valid part number.

thx!

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OK. i read the tread and am still struggling. I have this problem ... had the alternator tested at Advanced Auto ... they said it is putting out low voltage and needs to be replaced .... can i just replace the diode pack OR do i need to replace the alternator?

Also, i am having trouble figuring out what the appropriate part number is for the diode back .... FOOM-145-225 from the pelican parts forum does not seam to be a valid part number.

thx!

Try replacing only the diode pack it is simple and cheap....(see link) The part # F 00M 145 350 is a good one....

Regulator replacement....

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