Alternator problem - help

[vincematthews]

Did some work on the exhaust and disconnected the battery and removed the starter motor.
Now with everything back in place the voltmeter on the dash shows the alternator is not charging.

Checked with voltage with a good multimeter in place of the voltmeter.
Cleaned all connections between battery, starter and alternator.
0.2 ohm between +ve battery post and starter +ve.
Similar on -ve side.

It appears to be charging occasionally but mostly it doesn't.
Alternator/voltage reg. has been to an AutoElectric place who said nothing wrong with it.

Is there any other reason for 'not charging' symptoms - I still think the voltage reg. on the alternator is faulty . . . .

 

[ukmastiff]

When it it charging what exactly is the voltage with all items turned off and when it isnt charging what is the exact voltage

Regards

Mas

 

[vincematthews]

ORIGINAL: ukmastiff
When it it charging what exactly is the voltage with all items turned off and when it isnt charging what is the exact voltage
Regards
Mas

When charging its showing about 13.6V on the multimeter; when it appears not to be charging it shows about 11V . . . i.e., out of the car's voltmeter green section if it was connected.
Also when in apparently not charging mode, the reading doesn't change when the engine is reved.
The multimeter is connected across the voltmeter plug.
This is straight after starting when you would expect the battery needed topping up a bit.

Logic says it should be something I disturbed when doing the exhaust manifold work but I've been through all the connections cleaning them up.

 

[ukmastiff]

I thought 13.6 was slightly low TBH but a bit of Googling disagress with me so my old head may be failing.
Sadly I cant find my meter ( typical when you want it) I may be thinking of a strong 12 volt battery under zero load showing 14 to 14.4, this old age is a crippler []

How bout the headlight test ?

Start the car turn the headlights on and rev the car steadily upping the revs to a fair thrashing, then letting revs drop. Do your headlights go quite a bit brighter and dimmer ??. If they do strongly suspect alternator, if they dont it's highly likely that it is O.K. Saying that you will need to do this when your alternator is playing up if its an intermitent fault . When I was a tech longggggg ago , we all feared an intermitent fault arriving on our work bench []


Regards

Mas
;

 

[vincematthews]

ORIGINAL: ukmastiff
Start the car turn the headlights on and rev the car steadily upping the revs to a fair thrashing, then letting revs drop. Do your headlights go quite a bit brighter and dimmer ??. If they do strongly suspect alternator, if they dont it's highly likely that it is O.K. Saying that you will need to do this when your alternator is playing up if its an intermitent fault .

Sounds easy doesn't it! Intermittent faults, don't you just love them . . .
Started car, no fault . . . after a minute the voltage dropped so I thought do the test.
I reved the engine and the lights got brighter, then I realised the volts had swung into the green zone again so test void.
Tried this several times but couldn't get it to stay faulty for long enough, so no reliable results.
The lowest the voltage was dropping with headlights on was about 10V although I think if it had been running longer, it looked like it was going lower.
Maybe I ought to take the heat shield off the alternator so I can measure directly?

The other possible is a bad wire that is going high resistance under load . . .would this show the same?

 

[ukmastiff]

Personally I would want to test directly from the alternsator, nowhere else and by now I would consider how much of my time and stress was worth it before I'd get hold of another alternator to try at least []

Regards Mas

 

[bmnelsc]

Here is a link to the Pelican Parts page on diagnosing charging problems. It talks about 914s with a light vs gauge so substitute low voltage for "dim light". If you've already had the alternator/regulator checked out I would think you may have a wire-to-connector issue - either corroded in the connector, corroded wire under the insulation or wire broken down to a few strands somewhere. http://www.pelicanparts.com/914/914qa/914Q_electrical_alternator.htm

The other possibility assuming the charging system is good is grounds in the instrument cluster - see http://www.pelicanparts.com/techarticles/944_taillight/944_gauge_problems.htm I have read claims that cleaning up these connections corrected a number of gauge problems including the infamous low-reading fuel gauge.

Good luck

 

[colin944]

I would defo check volt regulator. I had the same prob a few years back with my 24. I drove myself nuts changing ires and cleaning up connections. The removed volt reg and took to my local vw guru who got me another for £12 and hey presto problem solved. I would remove your reg and check it agianst vw parts as most bosch alts use same parts. Then get one from a vw supplier ie gsf for a fraction of the cost from porsche.

 

[vincematthews]

ORIGINAL: ukmastiff
Personally I would want to test directly from the alternsator, nowhere else and by now I would consider how much of my time and stress was worth it before I'd get hold of another alternator to try at least []
Regards Mas

I know Mas . . . but sanity is cheap and anyway where's your sense of adventure? Don't you want that warm glow you get from diagnosing the problem and proving yourself right having only bought the minimum number of parts. Seriously though thanks for your ideas.

Cheers for the links bmnelsc I'll have a look at what it suggests tomorrow.
I have however replaced the wires a few years ago as they were burnt through.

Colin944, yes I would suspect the voltage regulator too but I changed it a few years ago.
I have sourced one on ebay at
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=120097643306&ssPageName=STRK:MEWAX:IT
which I may get as its not too pricey and is an easy option.

I notice that no-one has suggested the alternator itself is faulty? I suppose that must indicate they're fairly reliable.

 

[Mike_Pollock]

Alternator only wears contacts and bearings - I would check the regulator and the carbon contacts (I had one hardly worn and the other just long enough to contact), and take the belt off to check the bearings.

Intermittent faults!!!!

 

[vincematthews]

Well I connected direct to the alternator for measuring and it wasn't the wiring - turned out to be the voltage regulator after all, even though quite new and with decent length pickups.
The rotor where the pickups contact is quite worn (a problem for the future) and I checked the VR against an old Bosch one and it wasn't dimensionally the same - I think this may have had something to do with the failure.
Anyway fixed it just in time to take it to a Region 12 50th Anniversary bash - so thanks one and all for the comments.

At the bottom of my junk pile I found an old alternator which I was sure was for this car.
Is there a difference between RHD and LHD?
See attached photo for my alternator on the left and the mystery alternator on the right.


Does anyone know what Porsche its off?