New Battery and Alternator - Still won't start

New Battery and Alternator - Still won't start, not parasitic drain.

2003 Jetta TDI. Had alternator replaced less than a year ago.

Car sat undriven two days, and would not start. The battery performance had been degrading over time, so I assumed that my time was finally up to get a new battery. Put in an Interstate - the one specified for TDI, don't recall the number.

No problems for three days; let car sit overnight, stone dead in the morning. I can jump start with no problem. I can run radio, A/C, no problem. 14 Volts across the battery terminals when the engine is running, 12V when off.

Any ideas? Tests I can run?

check for amperage leaks

http://forums.tdiclub.com/showthread.php?t=238369&highlight=5+brake+light+mod

aggiegrad said:

2003 Jetta TDI. Had alternator replaced less than a year ago.

Car sat undriven two days, and would not start. The battery performance had been degrading over time, so I assumed that my time was finally up to get a new battery. Put in an Interstate - the one specified for TDI, don't recall the number.

No problems for three days; let car sit overnight, stone dead in the morning. I can jump start with no problem. I can run radio, A/C, no problem. 14 Volts across the battery terminals when the engine is running, 12V when off.

Any ideas? Tests I can run?

Click to expand...

Do you have an autzone or advanced auto parts near you? They will do charging system check for free. Your only other alternative is get amp meter & start pulling fuses. Are you leaving something on-after market radio? Trunk light -glove box light-brake light stays on?

__. Others have suggested looking at amperage draws which are pulling the charge out of the battery. That's probably your basic problem but there's also a chance that the battery is bad. Some of them are, just out of the box - it's not common but it happens. Check the battery.

All of the above is good advice. The current draw after about 5 minutes when the car is shut down and everything is off should be on the order of 20-40 milliamps (0.020a-0.040a). Very small draw - even a AA cell should be able to do that overnight. Either there is too much current or the battery can't hold a charge.

As has been stated - any aftermarket modifications???? (note to self, read OP sig...)

As a previous tech, specializing in electronics and driveability issues, i also strongly feel that a parasitic draw test is your best first bet. It is extremely rare (as in it happens, but after about six years as a line tech, i never saw it) to have an out of the box battery fail. And youve already replaced the alternator.

What the parasitic draw test is, is a way to narrow down what circuit the draw is on, and most of the time, tell you exactly what is pulling the current.

A brief description of the test follows as thus -

Youll need a particular tool, or make one yourself somehow. You need some way to connect a switch in between the positive battery post, and the positive battery cable. so the circuit is closed when the swich is closed, or open when the switch is open. This switch needs to be substantial, as it as to be able to handle the current from the battery without alot of resistance otherwise its gonna melt. The tool i have is a heavy guage metal body, with a screw in 3/8in bolt as the "switch" remove the bolt, the circuit is open. with the switch in place, connect an voltmeter on the miliamp setting to the two sides of the switch, let the car sit with doors closed, undisturbed for im guessing 5 minutes from the previous post, long enough for all the computers and circuits on the car to go to "sleep". disturbing the car in any way at this point. using the key fob, opening a door, anything like that, will wake everything up. After the 5 minutes, turn on the voltmeter, turn to the miliamp setting, and then open the switch in the battery cable circuit. you now have all the draw from the battery going through the voltmeter, as was stated, should only be 20-50 miliamps. Im guessing youre going to see much higher than that. if you do, start pulling fuses, normally, youll get to one, which drops the miliamperage down to acceptable levels. congratulations, you now know what circuit your draw is on. Now its time to set your voltmeter to its ohm setting, and start testing wires for short to ground or open circuits.

and there is no short easy explentation of how to do that im afraid.

Edit - just read your sig steven, saw you were an engineer, please excuse the language used in my post, didnt mean to talk down, as im quite sure you fully comprehend the concepts i was laying out.

Would a clamp meter work for this?

Grizzly,

Thanks for the tip. Parasitic current draw is one of my main concerns. Would a clamp meter work for this? Are they sensitive enough that I could put one around the positive terminal and do some troubleshooting in the fusebox?

-Steven

grizzlydiesel said:

(snip) A brief description of the test follows as thus -

Youll need a particular tool, or make one yourself somehow. You need some way to connect a switch in between the positive battery post, and the positive battery cable. so the circuit is closed when the swich is closed, or open when the switch is open. with the switch in place, connect an voltmeter on the miliamp setting to the two sides of the switch, let the car sit with doors closed, undisturbed for im guessing 5 minutes from the previous post, long enough for all the computers and circuits on the car to go to "sleep". disturbing the car in any way at this point. using the key fob, opening a door, anything like that, will wake everything up. After the 5 minutes, turn on the voltmeter, turn to the miliamp setting, and then open the switch in the battery cable circuit. you now have all the draw from the battery going through the voltmeter, as was stated, should only be 20-50 miliamps. Im guessing youre going to see much higher than that. (snip)

Click to expand...

__. Yes, this is a good description. And you'll need to find a way to do this with the hood closed. An open hood on a VW draws a lot of current for the under-hood lamp and also to energize the door lock and alarm circuits.

__. BTW, your under-hood, trunk and dome lights all go off when you close their respective doors, right?????

mrGutWrench said:

__. Yes, this is a good description. And you'll need to find a way to do this with the hood closed. An open hood on a VW draws a lot of current for the under-hood lamp and also to energize the door lock and alarm circuits.

__. BTW, your under-hood, trunk and dome lights all go off when you close their respective doors, right?????

Click to expand...

Yes. I have checked the "easy" stuff - interior lights and trunk light. I'll have to check the engine bay light.

Do I need a heavy-duty switch if I do all of my troubleshooting with the key out of the ignition? Can I just connect the Ammeter to the battery post and the other end to the clamp?

I have determined that a clamp meter won't work. Most only measure AC or are not sensitive enough for this.

OK, I'm stumped

All right. It's not parasitic current draw. I hooked up the battery to a charger (out of the car) and let it charge at 20 amps for about an hour. I put it in the car, reconnected the negative terminal, and connected an ammeter in series between the battery post and clamp. after 20-30 seconds, current draw is down near 20mA. If I close the hood, and set the alarm, current drops to about 12-14 mA after about two minutes.

I know it's rare, but I'm thinking bad battery.

What is your battery voltage before cranking then after?

Tony