epbrown01

I recently replaced the alternator in my 944 with a rebuild from 944-online and, since the battery had been drained to dead a few times *and* and don't know how old it is, I replaced it with a new Interstate battery. Car started fine and I drove it around the block to make sure the ALT light wasn't coming on anymore, and everything worked fine. I decided to bump the 944 in my rotation and drive it to work tonight.

When I came out 20 minutes later, I did my usual checks: power windows, wipers, gear shift, brakes, gas, checked the oil, coolant reservoir, and lights. While the car was idling, I turned on the lights and the engine died immediately. I restarted and tried the lights again - died again and this time it wouldn't crank anymore.

I had to leave for work, so I took another Porsche and left, but while my first instinct is the battery is bad (maybe from sitting) I wanted to check the board for 2nd opinions. Anything I could have messed up during the alternator replacement that would only affect the car when the headlights come on? I'm thinking that even with a weak battery, the lights shouldn't drag down the car that way if the alternator is working properly - shouldn't it provide enough power to run everything and charge the battery? Or should a night on the trickle charger bring the new battery up to snuff?

Emanuel

IceShark

The reason your car is dropping dead is the lights are knocking system voltage down enough that the ECU won't function. It stops working somewhere around 9 volts.

So your battery is probably at a low charge as it can't keep up with the additional current draw and the alternator is helpless. I would start looking at the alternator and the wiring to it and over to battery. Make sure the little blue exciter wire is OK as that is thin enough to be forgotten or snapped in half

It is also not unheard of for a "new" rebuilt alternator to be bad from the get-go.

silverBean

It could be a bad rebuilt alternator. i remeber i bought a rebuilt starter for my camaro, after removing the exhaust to get to it. Put it in and after 5 starst didn't work. Next starter did though.

Chris_924s

95 amps early.. 120 late. that dash is murder on voltage- especially if un-kempt.

tod84944

I know you hear this a million times on here.....check your grounds. My 84 had similar problems and turned out to be the gound coming from the fire wall to the block. Cleaned both ends and filed them down and cleaned the mounting point on the block. Also right above the mounting point on the block is the gound for the dme. Same thing, file, clean, and tighten back down. My car would run like crap when ever the fans kicked on. Wouldn't run when the head lights were tunred on.

MHT

? does the alt light come on when the key is on but the eng. is not running? Interstate rotates the stock in locations that carry their batteries, a weak battery is very unlikely. If the warning light doesn't come on before you start the car, the alt. will not charge. The 12v feed for the D+ terminal runs through the bulb in the dash. Make sure the blue wire is connected to the D+ terminal of the new alt.
Good luck

epbrown01

Okay, so I got off work about an hour ago and decided to pull the battery and trickle-charge so I could eliminate a dead battery as the issue when I went to work on it in the morning. I noticed that when I opened the door, the interior lights came on. Sure enough, when I inserted the key the oil and alternator lights came on, along with the seat belt warning buzzer.

The car turned right over.

I shut it down, and when i tried again it was getting no power - no warning lights, no buzzer, nothing. Next time, it turned over. I shut it down again and started it successfully five more times after that. Finally, I left it running and began trying the load the alternator - lights, air conditioning, defroster, heat, wipers, interior lights, radio, everything. The car stumbles when the AC comes on, but recovers. With all of the options on, the car runs but the alternator light grows brighter as various options are turned on. With no options, it's not on at all.

I suspect two things are happening: 1) I need to clean my grounds as suggested to eliminate the intermittent starting and 2) maybe the accessories belt is loose? I tightened it by feel - perhaps there's some play in it keeping the alternator from reaching full capacity. Thoughts on this?

Emanuel

IceShark

Could be the AC/alternator belt. That ususually squeals like crazy on start up when it slips but if it is glazed or really loose it may not make noise. The tension on the belt is supposed to be very tight - 85 foot pounds - which is a lot tighter than you would first think. You can do the push or twist by hand tension method but if you don't know from experience how hard to push that doesn't work the greatest. NAPA sells the kricket belt tension tool for only 10 bucks so you may want to pick one up and get a bit more scientific on tensioning.

It does sound like you also have a connection problem of some sort.

Charlotte944

What you are seeing is typical for the early cars because the alternator is under rated by about 20 amps or so. A secondary contributor is the age of the wiring and the condition of the various electrical connections and ground points.

Cleaning the grounds is always a good idea, but don't forget the starter and alternator connections.

Also, keep the battery, battery terminals, and battery box as clean as possible, ALL THE TIME. Use some form of corroision preventive on the battery terminals (I use Qualco Battery Anti-Corrosion compound, available at PepBoys), and for electrical connections that have a rubber boot (head lights, and so forth), use a dialectic grease.

951Porschiste

Are your positive and negative clamps tightened properly on the battery posts?

epbrown01

Thanks for all the tips, gang. I prowled around the engine bay looking at connections and definitely need to clean the grounds - everything on the firewall has some corrosion. I'll also get the Krikit (sp?) tool to check the belt tension for sure. Once tha's done and things are cleaned up, I'll give it another shot.

Emanuel

IceShark

If this is on your '83 944 and those are the original grounds, that could explain almost everything. Your car uses the bare copper straps which have now corroded like crazy - and the bad part is that there is corrosion between the copper conductor and the terminal ends. You can't clean that up without destroying the terminals. To cap it off you only have one strap from battery to inner firewall and another from the outer firewall to the engine block. Baaad News.

You need to replace with a later style ground which has two insulated cables, one from battery to firewall and another from battery to engine block. I sell them for $49 so it is cheap enough to do right.

An easy check to see if this is the problem is to take a heavy jumper cables, clamp both ends to the negative battery post, then one end to the body and another to the engine block. You are just adding 2 more grounds if you follow what I'm saying. If the problems go away you know what to do.

You may have bad positives also but the negatives are a sure bet.

Mike1982

Let me ask this, what happens if you put a battery that can put out more amps then the stock one? Would it crank faster? Would it not be good because the alt. couldn't charge it right?

IceShark

You should be in better shape. The battery will try and dump out as much current as it can for the load so the bigger the better, so to speak. There are other issues on battery type as in deep cycle which will not dump as much current as quick as a battery designed for starter duty, but as a general rule bigger the better. The issue would be (and where Emanuel's problems may lie) can the current get to the load? If you have bad wiring/connections there is going to be such a large reduction of current getting to the load (starter or whatever) that battery capacity doesn't matter so much as you are more or less screwed which ever way you turn.

The alternator will be able to charge up a larger capacity battery, it may just take a little longer if it is drained more. Again, don't worry about it. It is the system load and the connections/wiring that you are concerned with. With bad or too small wiring you can think of it as a water pipe with a bunch of holes drilled in it. Not all of what you put in one end makes it to the other. It is lost creating heat.