996 Alternator/Battery Problem
 

My (almost) always reliable 996 has a battery or alternator problem.

When I'm driving the charging voltage is about typically 13.2 Volts. This is definitely too low, but the alternator light never comes on, so I am not draining my battery while driving. I'm must be just keeping up, or charging.

After a short trip (15-50 minutes) the battery is usually very low, it either won't start, or just barely turns over enough to start.

I assumed my battery was bad, but when I took it for testing showed as 'good-but undercharged'.

I'm sort of at a loss now, I think I should change the alternator and get the charging voltage above 13.5 volts. But since the alternator light never comes on, I'm not sure why I'm depleting the battery on short trips.

Maybe it's both.... :confused:

What are you measuring the 13.2v with? It could also be just a bad connection.

Edit, Bad diodes would cause low voltage output from alternator, not sure what voltage your alternator light would turn on.

First thing is check all grounds . Make sure they are clean and tight . Add a smear of dielectric grease to every connection . If that doesn't help next is have alternator output checked .

996 is getting to the age where the cable between the alternator/starter and the battery might need to be looked at. It develops resistance, I had to change out the cable on the 997.1. Just a thought.

Funny, I just saw this posted in a few days ago. Sounds like it could fit the bill.

http://forums.pelicanparts.com/uploa...1755032999.jpg

I'd never heard of that issue before I saw the post above a few days ago, and now here I'm seeing twice in less than a week.

My car will occasionally start a little slow, but I think the battery is only 2-3 years old. I had wondered if the same issue may impact the boxster/cayman. It makes sense that it might.

OT -

We used to have a VERY highly respected shop here on the FAR west side of Houston in Seally, Rennsport Porsche Works. It was run by a guy named Mike Callas. I never took my car there when Mike was alive, but I have heard that folks had their cars taken there from far and wide and he was a well known figure in the Porsche world. When I heard about Tony Callas @ Callas Rennsport, I thought "what are the odds of 2 Porsche specialists named Callas?". Of course, one was in rural Texas and the other in Cali, and sure, there absolutely could be 2 unrelated Porsche specialists in different states with the same last name. Yep, I confirmed that Mike C of Seally, and Tony C of Torrance are father and son.

I'm measuring at the battery, at the fuse panel, and via the built in voltmeter. They all say pretty close to 13.0 volts when driving.

Also, this is a standard lead acid battery, not AGM.

Getting at the back of the alternator is almost impossible...I think I will try a spare battery, and when then doesn't help I will pull the alternator. I have a couple of Boxster engines laying around, same alternator according to Pelican.

Curious, why didn't they check the alternator at the same time they were checking the battery? Should be the same diagnostic tool.

How old is the battery? It might be right on the ragged edge of acceptable and pulling down the alternator.

A battery load tester is not the same as an alternator tester. At least, when I worked at a FLAPS ours were two separate machines.

When I had my battery checked last week at O'Reillys, they checked the battery, the alternator and the voltage regulator from the same hand held diagnostic tool, out in the parking lot.

Cool! I wouldn't think the only test of the VR would be seeing what the V is while running. I'm not sure how it would test the amperage of the alt other than just seeing that it was putting out the proper voltage. I know that the machine that we used to us required the alt to be out of the car. We'd mount it to the machine, strap a belt around it and then it would tell us the output and say if it was good or not. The thing that you describe, able to load test a battery, check voltage and test alternator, is awesome!

I think Glenn took the battery out and took the battery to the store in his wife's Macan, so they would only have been able to test the battery which is all that's needed if the battery is at 12.6V and fails the load test.

It's only a couple of years old. But it gets six months of use, then six months on a trickle charger.

Because I took the battery back to the desk in a shopping cart....

The easy test for an alternator is just output voltage, the real test is on a bench with a proper load.

I had a Subie with a bad battery years ago. FLAPS guy tested and said it was fine. The guy at the dedicated battery store laughed when he tested it. It was indeed bad and swapping it out fixed my problem.

THat's how we always tested it.
What'd they do, just put a voltmeter on it?

I’ve experienced the same, that was part of my thought process for the first suggestion.

They hooked it up to whatever battery tester they have at O'Reilly's. I had hooked it up at home to a voltmeter and it was showing like 12.8.

Weird. You must have gotten one of the rocket scientists or they had a crappy load tester. There's not much to testing a battery. Connect the tester, hit the button watch the needle.

I suspect the 'combination test' is simply a voltage check on the alternator output.

I thought the same thing, except my charging voltage is borderline. But since the alternator light never comes on I 'think' I'm not draining the battery while I'm driving.

I'm going to install a known good battery and see what happens. That's a lot easier than swapping the alternator.

Yes, change the battery first.

Akin to Maslow's hierarchy of needs, I have a hierarchy of ongoing car repairs.

I think my daily driver V70R is sorted with a new alternator (terrible job to remove/reinstall), a new (used) throttle body (another terrible job in ultra-confined space), and the new summer tires (finally) on the repainted summer rims.

So now...the Volvo battery and the 996 battery can change spots for a week and we see what happens...