Hi all,

I am having a bit of electrical troubles where I loose power and have to charge the battery at least once a week. Also when idle the car will sometimes stop.

Car is an 1984 ROW auto.

Last night as I was testing some relays (no. 24 for the interior fan) the car was idling when it suddenly died. When I tried to start it the battery had run down.

So today I made som measurements:

1) The battery reports 12,7 V after a charge.

2) Measured at the battery with the car at idle I get 14,4V - and the same when running at 3000+ rpm

3) The voltage indicator in the dash shows a voltage just short of 14V when idle (se picture).



...so alternator / green wire seems not to be the problem.

4) But when I turn on the running lights the dash voltage indicator drops down to 12V (when idle) and if I let the cabin fan run it falls even more (I forgot to measure the drop at the battery)

5) When idling in the driveway with lights on I noticed that the voltage will go up and down and the engine (that normally runs well) is on the verge of stalling. If I rev it, the problem goes away. Please see the video of the issue here: https://dl.dropboxusercontent.com/u/...81/928idle.mov

6) I dont seem to have a battery drain problem as the car will not consume a lot of power when just stored. It is almost as it runs down the battery when driving? Or a least: When driving slow (below 50 km/t)

So basically: I get 14,4V when idling but it drops really fast when the car starts using power (lights and / or cabin fan) - and that might effect the idle. What might cause this?

So do I have an electrical problem? Or an idle problem? Or?!?!? Any pointers would be great to work from :-)

Regards

Lars

Edit: Yes I know my tach is acting up, I am to lazy this summer to find the loose connection somewhere :-)

 

Have you cleaned your grounds and checked your ground strap for corrosion?

 

Forget your dash indicator and run your tests at the 14 pin connector jump post in the engine bay. I've had a good number of cars with your symptoms and it will either be the alternator not being able to keep up or you've got a bad wiring harness from the starter to the 14 pin connector. This is the main feed and they get pretty bad.

Here's an example.

 

Thanks Sean,

I recently had the oil pan gasket and engine mounts replaced (by a local 928-shop) and that might have strained the cables. Also: I deleted the air pump and replaced the starter myself some months ago.

I will take a look at the 14 pin connector / jump post. Great with some pictures - but a stupid question: Where in the engine bay can I find it?

(For some reason I have been spared electrical problems until now - so this is all new to me :-)

Regards

Lars

 

On the right side of the car inside the engine compartment and on top of the right side side coil.

 

Thanks soontobered84,

I will hunt for it later today.

Also: Now I have a bad battery or at battery drain issue as well - when I tried to start it this morning the battery did not have enough juice to start the car.

Even though I charged the battery yesterday and only started it 3 or 4 times when I did my measurements.

Battery is approx. 4 years old but have had some cold winters (-5 to -10c in the garage) so that might have aged it a bit. Did have it trickle charging some of the time though.

How likely is a bad battery to be the core of the issue?

My experience with these cars is that you can keep throwing money at the problems (new battery, new alternator, new harness) so I better get down to it and measure at post / clean grounds / check 14 pin harness...

BTW: Do any of you have a diagram of all the ground spots on the 928? That would be a great help.

Regards

Lars

 

Deep discharging these batteries shortens their life and is likely to reduce the batteries capacity. Definitely spend more time investigating and getting to the root cause before spending any money.

 

Certainly not your only problem, but worth checking - The alternator belt must be much tighter than you would expect...

 

Thank you for all the ideas and pointers!

I had a quick look at the 14 pin and the alternator belt.

1) The harness / 14 pin seems a bit loose so I tried to settle it a bit more firmly. A quick start of the car gave a more smooth idle, but that might be wishful thinking :-)

The connectors seemed fair with unbroken wires but a little bit dirty at the points. Could use a cleaning at some point.

The female end of the pin (car-side?) could use a bit of cleaning as well. Don't know if it should be taken apart (don't mess with old brittle plastic!) or a quick spray with contact cleaner is the way to go?

The cables to the 14 pin seemed ok, but the big wire had cracks in the insulation and some corrosion on the car side where it connects (see picture).



...so obviously its a good place to start.

2) The belt for the alternator was ok, but not overly tight. With a firm press with a finger I guess there is about 1 cm / 0,4" of play. A little bit too much? To bad I have go under the car to reach the adjuster.

BTW: I measured Amp draw on the car with everything off except the digital watch and it showed 1,08 Amps. Is this within the normal range?

Regards

Lars

 

Looks like you've found a potenial problem, wire looks like one pictured earlier.

Brian.

 

1A draw is too much, if you have a 75Ah battery it will last 75 hours. Try watching the current draw while removing fuses/relays to locate the problem. A relay might be hot which is also a clue.

 

I suspect the alternator isn't working right and may be a source for the current draw which is cetainly much too high (should be ~ 25mA) - so you are >40 times too much.

See if you can disconnect the alternator and check for current again.

Seems the alternator van generate but not very well - maybe you have lost a phase. A good alternator shop will be able to test/refurbish it.

Alan