Charging Issue - Guru needed

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There I was thinking that Porsche ownership would be simple ...... Some of you would have read that I have had a couple of problems with my C2 Cab recently, the major issue being that an oil breather pipe failed and discharged oil everywhere. After some brilliant work by Parr at Crawley, the Car is beautiful .... except .. The alternator was contaminated by oil and had to be replaced. I am now experiencing inconsistency in the voltmeter readings as shown on my dash. Sometimes .... turn ignition on, voltmeter reads 12V, start engine voltmeter reads just under 14V ... GREAT, but ... sometimes turn on ignition, reads 12V, start car, still reads about 12V( ever so slightly over) If I put the chargiing system under load by turning on all electrical / lights, no change. The car starts fine each morning .... The wonderful people at Parr are scratching their heads and I was wondering iof there was anyone on the forum who could shed any light on this weired behaviour.. Thanks.

 

[John Ware]

Silly question probably but how old is your battery?

 

[Diesel130]

Hi,

This should not be rocket science to diagnose. The components involved are alternator, voltage regulator, battery and voltmeter on dash. I don't know whether the voltage regulator is an integral part of the alternator in the 996 or not, but that would be my first point of investigation. The second one would be whether it is simply the dash voltmeter which has a 'sticky' needle and not showing the correct value.

Either way, measuring the battery voltage at the terminals with an external voltmeter should indicate whether the alternator output is correct or not, once the engine is running. It should be between 13.8 to 14.5v.

 

[TonyS]

Hi guys,

I don't think there is anything at all wrong with my charging circuit, but I do get very different readings when I start the car dependent on how long it has been standing. I put this down to the drain caused by the alarm etc. If the car is left for a week, then the battery only just cranks the car (new battery) so there is evidently some BIG current being drawn even when standing. I now charge the battery every weekend, overnight.

Hope this helps - seems a normal issue to me (providing your battery is good as mentioned by John).

tony

 

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Minus 5.5C this morning, turned ignition on, showed less than 12 V, Three turns Car fires up as if Battery is fully charged. ... Drive Volt meter showed approx 12.5V, stop turn off, remove Key, Volt meter shows 12V with key out ?. ... Perhaps as Richard suggested the Gauge is sticking.. Yesterday had one drive where showed 14+ V. Richard you mentioned that the needle may be sticking, is this a known prob, and is the cure a new gauge, or do I have to have a complete instrument cluster. ... or can it be fixed using big hammer technology. My Independent, has a spare Instrument cluster which allows them to test for this so might have to go back again.

 

[TonyS]

Sounds like it is broken to me. According to my 986 (Boxster) manual the instruments are integrated into one cluster and this can be tested for function using Porsche System Tester 2, and has fault memory, although the Boxster did not have a voltmeter fitted, so I can't be sure it is integrated.

 

[TonyS]

check voltage at the battery with engine running before you do anything else! (as mentioned above)