Former VWDieselParts.com Forum

I have a twice recurring problem i can't seem to diagnose - have looked at some threads here but can't seem to solve it. I drive a 89 1.6d NA jetta.

Essentially my battery has died twice after about an hour of highway driving, two separate incidents, about three weeks apart.

The engine was rebuilt about six months ago, and has been driving great since then, and i've put about 3000 miles on it. Then, three weeks ago, about an hour into a hour and a half trip, my gauges started to fall slowly, and my lights dimmed. When i stopped i found my battery was completely dead.

Since it was a four year old battery i just replaced it, but then tested with my alternator and didn't seem like i was getting enough voltage under load, so i replaced the alternator, too, as that was at least 60,000 miles old (came with the car). Figured since i just rebuilt it i didn't mind just springing for the new parts.

Everything after that worked great - for about 1000 miles and several long trips.

Except yesterday then the same thing happened. Hour or so into the drive, dimming lights, low gauges, and when stopped, dead battery.

Took the new alternator and tested it, works fine. Tried to jump the car with the girlfriends car and wasn't able to even jump it, even after letting her car charge up my battery for a good 15-20 minutes.

I then switched our batteries, and with her battery in my car, it started up just fine. Then using my car (with her battery in it), i jumped her car (with my battery in it), and let it run for a good 20 minutes. Tried to restart it, and the battery was still dead.

Now i've taken the battery in, had it tested (they said it was far weaker than it should be), and now they are charging it up again.

So next i'll put the charged up battery in, and see how it maintains, but i am concerned that it's actually not the battery but something going on in my car that is either draining too much juice on long drives for the alternator to keep up with, or perhaps over charging the battery and frying it. I can get the battery replaced under warranty, but i don't want to just keep going through batteries...

Any ideas on what else to troubleshoot here? I have replaced the glow plug relay, wondering if that was faulty and perhaps not shutting off, draining the battery. I checked the voltage regulator, and it looks fine to me. Brushes are intact and barely worn. All the wiring out of the alternator looks good - i replaced the ground clip that looked a little corroded, but not the extent i think it was faulty. I also read here to check the radio fuse, so checked that and it is fine.

I have a hour and a half trip ahead of me just to get back home, which i'll make tomorrow in the daylight in case it happens again, so at least my headlights aren't draining the battery...

Thanks for any help!

You really need to do a current draw measurement on the positive wire to the battery. This is not going to be easy under the circumstances but you need a decent clamp on ammeter (DC) to measure with since the current will be larger than any multimeter can handle. With a fully charged battery and the engine running at say 2000 rpm you need to see if there is some current draw that could be draining the battery or if the current is flowing the other way into the battery which would indicate that it is charging. You should also double check all connections including the battery terminal and cables for any looseness or corrosion anywhere. If the alternator tests out fine in a good alternator tester, then you also need to check the alternator output in the car to make sure things like the exciter wire is actually getting power at the alternator to get it into charging mode and so on. Voltage tests can also give some ideas of what is going on (see below)

Some of these tests can also be done with one of those cheap harbor freight multimeters (free with a coupon or just a few bucks on sale) so you can see if your battery voltage is significantly less than about 13.2 volts when the engine is running at about 2000 rpm or so. If the alternator tests good and the battery tests good the problem would likely be in the wiring between the two and/or a connector or even the ignition switch. The charging output of the alternator is directly connected to the positive battery terminal and the wire that controls the alternator output is what makes it charge the battery or not. So, if battery voltage keeps dropping with the engine running and something like parking lights on, that alternator is not charging the battery.

Hope all this helps. It's harder for me to advise than it is to do the testing so hopefully I have given a decent amount of clarity here.

The symptoms sound like bad cables. Check the neg to tranny and chassis, pos to starter and alternator for corrosion, damage, bad fasteners.

I'd get a cheap DMM and run some wires from the battery into the cabin to watch the voltage at any time.

~13.5V when running, ~12.5V when not. Watch voltage when glows are on, cranking and right after startup (post-glow).

I rigged up a voltmeter in my winter Jetta so I wouldn't be stranded with a low battery too. I found that my idiot light for the alt sometimes wouldn't illuminate when you turn they key on, and when you start the car, the feedback signal to the alternator is run through the idiot light, and the car wouldn't charge. Gauges would get funky, like the tack would start sticking at 2000 RPM, but my that time, it was nearly too late. The car would later start though (low voltage would kill the high pressure fuel pump - it's a gas car).

I've also had the voltage regulator come loose on my alternator before, and that just flat out bakes the battery - deader than dead. You may have a flaky wire going to the voltage regulator, or the mounting means is losing it's signal to ground (negative) and then putting out max charging to charge what it thinks is a dead battery. After I stop, I can usually smell sulpher from the baking battery, but by that time, it's too late.

Thanks for this advice. Very helpful.

I picked up the battery and it's completely toast. They don't even expect it to hold what little charge it has overnight.

Makes me imagine i'm overcharging the battery somehow and killing it. I'm going to get towed home tomorrow where i can get a new battery under warranty, so i can perform some of the tests you suggest.

Does the voltage regulator have wiring specific to it that i should examine? All it know of is the element that screws into the alternator housing. The regulator itself looks functional, and since it came new with the new alternator and my similar symptoms occurred with the last regulator, it would seem that if the problem is the regulator, it must be in the wiring somewhere.

I did glance in the dark at the neg cable connection to the starter, and there is some corrosion there. Nothing that screams for replacement, but i'll replace it nonetheless and see if that helps.

I'll also check the glow plugs with the old relay while running and make sure there was no additional draw from plugs that didn't shut off.

What are the different ranges in battery power while running that i should be looking for? With 13.2 as the goal for 2000 rpms, what would constitute too low, and what would constitute too high? I've read differing accounts from different sources, so not quite sure where to land.

Thanks again for the help.

x2 check grounds, but all grounds and pos connections too, run an ohm meter to wires just to check, voltage drop test.
i ran a new ground from alt top to a good body ground(among others), you may need to ground more. on the ground side of batt terminal you should have 2 wires grounding to body.

StevenPH wrote: What are the different ranges in battery power while running that i should be looking for? With 13.2 as the goal for 2000 rpms, what would constitute too low, and what would constitute too high? I've read differing accounts from different sources, so not quite sure where to land.

if your only getting 13.2v@idle thats too low, 13.5@idle is low. my bosch puts out 14.3, my nonname brand alt last i measured @13.8v. sounds like a charging problem, belt is good? new alt isnt working right. like i said^ check your grounds are good, you may need to run new grounding. i did and it helped in an instant

What you should do is measure the battery voltage before you start the engine, and measure it after it's running and the RPM has been brought up enough to engage the charging mechanism in the wiring. You should see a .7V or greater difference, or something along those lines. That way you will know that the alternator is putting out voltage, whether it has any amperage to it or not, that's not measured with a voltage test. Some alternators have failed to charge a battery when they have output enough voltage. Just so that everyone knows that because it has voltage doesn't mean 100% of the time that the alternator charges. But, there's something going on here. If the car dies because the battery is dead, then this tells me that there's something going on with the alternator/wiring part of this equation, or basically what charges and runs the car. If the battery is dead and the car is running, the alternator should be able to keep all the electrics running for as long as needed until you shut the car off. So, if the battery dies and the car eventually dies, something regarding the charging or main power to/from the alternator isn't right.

I think may have found the problem - bad corrosion with no connection on a ohm reading on the positive cable direct from battery to starter. The whole post on the starter is badly corroded underneath the nuts, so i may just replace the whole starter as it came with the car and has a junkyard marker on it.

I also took ohm readings on the ground wires, and found when i connected the ground terminal on the alternator to the neg post on the battery, i got only half the ohm reading i was getting everywhere else. When i ran a temporary wire from the alternator's neg post to the block, i got a full ohm reading between the post and the battery.

In this case would you advise to also run a permanent ground straight from the alt. neg post to the body? There is no otherwise justifiable reason i would be getting a lower reading there, right?

In addition, now i've found myself in an interesting situation i didn't expect - when i removed the starter the learned that the starter bolts are also the front engine mount bolts... and now with the engine settled a little and the pressure off the engine mount, there is a solid inch of travel between the mount and the starter bolt holes in the tranny.

Jacking up the the tranny only lifts the entire car, as i assume the other engine mounts are still holding fast enough to not give in the front.

Other suggestions for getting the starter and bolts back on?

I'm doing this in the street, so if i have to get serious here in removing other mounts or lifting the engine from above i'll just have it towed in somewhere.

If you play around enough with the transmission, it should move around enough to get the bolts back in line. These MK2 starters are a pain to replace the starter. You may have to jack it up and actuate the clutch so the pressure plate and clutch disc aren't against each other in order for things to move. I've always supported the engine/trans with a jack while doing a starter because of this, and I don't know what's holding them from going back together.

Just so i'm not creating more problems - is the lower, smaller bolt with the blue wire a ground wire? It is the wire i'm getting a low ohm reading with the neg battery post.

i hope you know you disconnect power source when getting an ohm reading; iirc if your doing an ohm reading on say a wire you disconnect wire so your measuring just the wire. an ohm reading can otherwise include everything its attached to.

If I remember correctly, that blue wire runs to the idiot light in the dash. If so, it's reading ground, through the LED module on the instrument cluster if you didn't disconnect anything else when measuring the resistance. If it's like my 86 Jetta, it's an integral part of the charging mechanism for the alternator to properly charge. Is your idiot light functioning in your instrument cluster when you turn the key on?

I see. Yes the idiot light functions fine.