Five-8

Hi All

I am trying to diagnose a charging issue.
Symptom--Last trip in the car, voltmeter became erratic, and then started to intermittently peg to the top...noticeable power drain could be felt while driving while the needle was "pegged", power drain went away when the needle would return to "normal" position.

Just replaced the alternator this morning with a unit i got from Roger last year, readings at the jump post are exactly the same as with the alternator i just took out.Only difference between the two alternators seems to be that with the new alt, the voltmeter reads low (less than 11) but now does not respond to throttle input(the old alt did show a jump on the voltmeter).

Jump post reading with car off shows 12.5 (same as the battery)
Jump post reading at idle with nothing on 12.2
Jump post reading with everything on shows 11.6 at idle
Jump post reading at 2000RPM shows no change whatsoever.

Front wiring harness is brand new (Starter to 14 pin)
Battery ground strap is new
Grounds have been cleaned many times(but not yet this year)

I believe the exciter diode in the pod to be bad, because i do not get the warning light on when the ignition is turned to on.Light does work i saw it briefly yesterday(low voltage condition)

Could the exciter diode cause the above behaviour?

I know the battery is not at its best, but is it possibly the culprit here?

Possible that the new alternator is bad too ?as is the old one?

Something else i'm missing?


Appreciate some advice

Thanks as always.

dr bob

I'm not aware of any "exciter diode" in the pod. The excitation circuit comes from 15 (ignition on), through a resistor and the light bulb in parallel in the pod, then the CE panel, the 14-pin by the jump post, and through that front-of-engine harness to the alternator.

While it's possible the resistor and light bulb in the pod failed, it's much more likely that the exciter wire to the alternator is open somewhere along its route. Telltale is that the bulb doesn't come on with key on but engine not running.

Most common places to look are at the 14 pin connector by the jump post (pin 1, blue wire), and at the end by the alternator where the same blue wire connect to alternator D+. Corrosion in the pins is typically the challenge at that jump-post connector. The pigtail out of the harness to the alternator can get damaged when the alternator is allowed to hang by the wiring during removal and installation. The terminal on the wire end can get corroded too.

You can test for function between the key and the 14-pin connector. Disconnect the engine sde, and identify pin 1 in the car side of the connector. With key on, you should read close to battery voltage there, meter referencing ground. You can verify the function of the pod light by grounding that same pin 1 on the car side of the connector with the key on; alternator light should glow.

You can use yopur meter to test the wiring between the 14-pin and the pigtail to the alternator, using the Ohms (resistance) function on your meter. with key off and the 14-pin connector lifted, connect the meter between pin 1 on the engine side of that connector, and the connector on the blue excitation wire at the alternator. It should show close to zero Ohms.

Be aware that there's a service alert that includes changing the resistor in the pod when swapping a later alternato into an early P-R-fitted car. the excitation requirements for the Bosch alternators are slightly higher.

Five-8

Thank you Dr Bob
You of course are correct, resistor/ bulb is what i should have referred to it as.
I will have a look at the 14 pin, thanks.
Is it possible that the resistor/or a bad connection in this route be responsible for the no charge condition?

Thanks also for the service alert with respect to the later alternator, the new one is a Valeo so i will search out this as well.

Cheers!

Five-8

Following Dr Bob's instructions

10.38 measured at pin 1 on the 14 pin with key on( is this close enough?)
0.01 to 0.00 resistance from pin 1 to alternator (no surprise-fresh harness and alternator)
cannot get warning light to light when grounding out pin 1(resistor is in fact no-op?) Or problem in the connection further up the line?

What would this suggest?

Thanks!

Five-8

So after a long day of trying to problem solve without success, i decided a beer or two was in order.

Its good to remind myself that working on a 928, isn't really something i have any right to complain about.

Still love this car, even if it has been more often an ornament than a car i can drive and enjoy for the last couple years.

Cheers,



Cheers,

Landseer

What model year?

SeanR

What condition is the harness? It wasn't yours I built this morning was it?

Five-8

Model Year is an 82 US 5 speed.

Harness is/was new from Carl...i put it in last year...car hadn't been anywhere except for in the last couple of weeks(because of other issues) and all seemed fine until this erratic voltmeter behaviour...can't see how the wiring harness is problematic...i did get a a half dozen tours in over the last month...but now clearly i have an issue that must be righted before venturing out again.

Cheers,

The Deputy

Maybe this may help.

http://www.stuttgartperformanceengin...SHPROBLEM.html

Brian.

Five-8

Brian, that is helpful, Thanks

Cheers,

Alan

This is too complicated, start with what is most logical - a wiring break.

Does the charge warning light come on in bulb-check (before start)?

Unplug the 14 pin connector: test for voltage (wrt ground) on pin 1 (blue) of the car side (bottom) with ignition off should be 0, test again with ignition on - should be battery voltage, compare to jump post voltage.

With ignition on - short pin 1 of the 14 pin on the car side to ground, have an assistant check for the charge light coming on?

On the engine side of the 14 pin connector test for voltage on the pin 1 blue wire, it should be 0v.

Reconnect the 14 pin connector, with the ignition on what voltage is on Pin 1?

Alan

Five-8

It does not.

Tested-Ignition off -voltage 0
Tested Igniton on -voltage 10.33
Jump post voltage -Ignition off -12.44
Jump post voltage -Ignition on -12.14

Grounding out pin 1, ignition on of course===no light


Confirmed this.

Voltage is barely visible (0.06)---this can't be right can it?

Alan[/QUOTE]

Cheers,

Five-8

ummm...so i just went back out to check the jump post voltage and the warning light is now lit????

have i somehow jogged the connection at pin 1????

WTH???

Edit;Perhaps this was just a low voltage warning.

Cheers,

Five-8

I actually have a new resistor and bulb assembly, would it make sense at this point to replace them or is there a potential for damaging these new components?

Cheers,

Five-8

15 mins later...light is not functioning again...i did not start the car, just turned the ignition off while the light was working, came back and now is not working again.

is this helpful in understanding the nature of the problem?
Admittedly i know very little, so i don't know what to make of this.

Cheers,