alternator help please

shemp4 · 04-07-2006, 06:26 PM

hi, new to the forum and to porsche ownership! here is the problem (1985 944) , car would not start seemed like a weak battery , it was turning over but kinda slow. i brought battery to have tested and it checked out fine. i charged it and car started right up and ran fine. a friend suggested to check alternator, he said while running disconnect battery and if it dies its your alt. i did this and it died right away! so i removed the alt. and had it bench tested and they said that it was good. now i am at a loss i have no idea what to do next. thanks in advance. joe

legion · 04-07-2006, 06:46 PM

Bad grounds.

Try replacing the ground from the negative side of the battery to the bell housing.

Oh, and do you have an early '85 944 or a late '85 944?

shemp4 · 04-07-2006, 06:59 PM

thanks i will try that. its early 85

shemp4 · 04-08-2006, 10:11 AM

i checked the negative battery terminal and wire to chasis and cleaned them. volt meter shows 16 + when car is not running and 14+ when running any ideas???

onZedge · 04-08-2006, 10:16 AM

A FRIEND SUGGESTED WHAT !!!

NEVER DISCONNECT THE BATTERY WITH THE CAR RUNNING - YOUR ELECTRICAL SYSTEM CAN RUN UNREGULATED - AS MUCH AS 60VAC - WILL FRY THE DME AMONG OTHER THINGS IF THIS DOES OCCUR.

Some friend.

Make sure the alternator is properly grounded and the mounting bolts tight first before you begin troubleshooting. Having the battery and alternator checked, as you did, is a good start. But before you throw money at replacement of suspected bad parts, try a few simple checks first.

Simple checks do not cost anything. I like free. Free is good. Saves money for important stuff like suspension upgrades and short throw shifter kit. As a new watercooled 4-banger owner, these are the most bang for your buck following replacing all vacuum hoses and cleaning all the grounds. But I degress...

Check all the battery cables with an ohmmeter to make sure they are way less than one ohm. If greater than 1/2 ohm replace it. Is the "charge" indicator light bulb good? It is a critical part of the circuit. The alternator needs at least 2VDC at the small terminal (blue wire I think) in order to flash the stator so the alternator will charge. The alternator gets this voltage through the charge indicator bulb, but under normal circumstances, you will not see it illuminate with the engine running. There is a connector (two wires) in the engine compartment above the brake booster that has a big red wire (from ignition switch to starter solenoid) and a small blue wire (from charge indicator bulb to alternator field terminal). Back probe (stick the voltmeter probe into the back of the connector without unplugging it) the blue wire on the connector to see if you have at least 2VDC with the car running. If you don't have 2VDC it's probably not a bad alternator and you have a wiring problem. If you do have at least 2VDC remove the air cleaner housing and check the resistance of the blue wire between the unplugged connector and the field terminal on the alternator. If more than 1/2 ohm replace the wire. If way less than one ohm, have the alternator re-tested at a different shop - an alternator will test good with a bad diode. The alternator bench tester operator may not have been experienced enough to notice the diode trouble lamp on the bench tester. If the voltage output meter on the bench tester is anywhere near marginal, replace the voltage regulator (bolts to the back of the alternator). If your battery is still not charging, check for a parasytic voltage drain with the car off. Connect an ammeter between the positive terminal on the battery and the disconnected positive battery cable. You should read milliamps. If not, start pulling fuses, one at a time, until the currnt drops substantially. That will be the circuit to check next, but I will not get into detail about that here. Dont forget to check your aftermarket big honkin' stereo fuses for parasytic drain also. Most stereo shops do not take the time to properly install equipment wiring IMO. Slap it in and get the car out of the shop quick- time is money. It's not MY car - what do I care attitude. I've seen too many customers come into my store with complaints of charging problems and dimming lights AFTER their new honkin' stereo was installed. These include improperly sized wiring and fuses, improper or disconnected grounds, etc... Also, nobody ever considers the battery charging capability of the stock alternator when big honkin' amps are added.

Shoot, I didn't mean for this to be a long post, but I hope it is informative.

shemp4 · 04-08-2006, 01:44 PM

thanks for the reply!! the alt. bulb does not come on when ignition is on. so i will replace the bulb and see what happens. thanks, joe

Granite 944 · 04-08-2006, 07:25 PM

Quote:

Originally posted by shemp4
i checked the negative battery terminal and wire to chasis and cleaned them. volt meter shows 16 + when car is not running and 14+ when running any ideas???

THIS is not making sense.

"16+ volts when car is "not" running"? check again. "14+ when running" sounds about right.

Check out the connectors and their condition AT the STARTER motor, the connections at the battery and down line from it, and please go to Clark's garage.com and look at the diagnostic checks/suggestions there regarding this. Good luck!

SoCal Driver · SoCal Driver's Garage

Check the grounds from the engine to the chassis as well as the ground from the battery to the chassis. Also check and replace the positive battery cable IF there is an after market end at the battery. After market ends clap onto the large cable. Factory has the large cable soldered into the end. The large red wires are what feed the current into the car. Make sure these are clean at the fitting also.