924Board.org

[Jazzerpet]

Yes I know 944’s are not our forte but I thought maybe someone might have a suggestion or two.

85.5 944, I have replaced the alternator and what I believe is the voltage regulator that mounts to the back of the unit. There is also a smaller item on the back I did not replace.
I noticed when I first start the car the gauge reads 12 volts. Then after about 30 seconds it went to around 14 volts. There have been times it did not rise. The other night it went to 0. I hate sitting on the side of the road in a Porsche, good thing it was dark. Anyway I got it home and was a few days before got a chance to charge the battery and start it. This is when I noticed the how the gauge rises.
BTW I replaced the alternator originally because it left my son on the side of the road and was not charging. The old alternator tested good but I figured it was going out intermittently.
_________________
1980 931
1985 ½ 944
Member of the “Omaha Crew”

[Paul]

If it went to zero, you have a wiring problem or a bad gauge. It's almost impossible for the battery to suddenly go to 0 volts. That said, I'd do a load test on the battery to make sure you don't have some dead or shorted cells.

[Jazzerpet]

The battery is new, I put a die-hard international in it. The gauge went to 0 due to driving at night without the alternator carrying the load. The problem lays somewhere in the circuitry that excites the alternator. I am ignorant as to what that circuitry is and what part of it would cause an intermittent problem like this.
_________________
1980 931
1985 ½ 944
Member of the “Omaha Crew”

[Sleykin]

Believe it or not the exciter voltage gets to the alternator thru the idiot light. If that light burned out it would have trouble self exciting. With the motor off or the alternator not charging it is a path from the battery to the alternator and lights up as well as supplying a "start voltage" to the alternator. Once the alternator is putting out the voltages on both sides of the light are equal and it stays out.
Or you could have a broken wire.
_________________
Glenn Neff
Medford, OR
87' 924S

[Jazzerpet]

The light below the alternator gauge lights with the key on and the engine off. It goes out once the engine starts. It would be that light correct? I read something about that in a different post so I checked mine a wile back.
_________________
1980 931
1985 ½ 944
Member of the “Omaha Crew”

[Jazzerpet]

Ok I went a little further on this. I searched the old posts and came up with this PDF link left by Smoothie. I went through the tests it lists.

WIRING CONTINUITY TEST
1) Connect a voltmeter between alternator Red battery
terminal wire and ground. Voltmeter should indicate battery voltage. If not, check wiring between alternator and battery.
2) Turn ignition on. Ensure alternator indicator light comes
on. If light does not come on, check wiring between alternator and warning light, including indicator bulb.


Test #1 I have battery voltage 12V.
Test #2 The light comes on. (I assume this is the light under the gauge)



ALTERNATOR EXCITER CIRCUIT TEST
CURRENT CHECKING
Check that battery voltage is a minimum of 12 volts. Charge
as needed. Disconnect Blue wire from alternator terminal and connect Multimeter (US 1119) between alternator terminal and Blue wire. Set multimeter to 200-mA range. If reading is lower than 150-185 mA, check Blue wire between alternator and instrument panel or replace printed circuit in instrument cluster.


On this test I have 12-mA Not good.



RESISTANCE CHECKING
Disconnect negative battery cable. Disconnect Blue wire
terminal of alternator. Connect Multimeter (US 1119) between Blue wire and battery positive. Turn ignition on. If readings is not 140-160 ohms, replace instrument cluster printed circuit and recheck.


On this test I had an open condition. No ohms reading.


So this tells me that the printed circuit board is bad. The tests provided are for the 1990 Audi 100. So my question is, does the 944 have this printed circuit board as well? If so how much of a pain is it to change?


One more note, The blue wire reads 12 volts wile the car is running
_________________
1980 931
1985 ½ 944
Member of the “Omaha Crew”

[Jazzerpet]

Bump, Any help welcome
_________________
1980 931
1985 ½ 944
Member of the “Omaha Crew”

[Sleykin]

Measure the voltage at the battery with the engine running. If it is 13.5 to 15 volts your alternator and regulator ar ok. If your dash light comes on before you start and goes out after you start then your charging and exciter circuits are probably ok. That leaves the dash guage. Check the guage and wiring to the guage. I don't know about the printed circuit board but if you have one it could have bumped a ground and blown a trace. sometimes you can repair that with a short piece of wire and careful soldering.
_________________
Glenn Neff
Medford, OR
87' 924S