Mechanics

DO I HAVE A SHORT OR A BAD GROUND SOMEWHERE?

1997 Mitsubishi Montero • 200,000 miles

Hello, I have a 1997 Mitsubishi montero sport. I've been having the same problems about every 6 months for the last 2.5 years now. The car runs great for 6 months and then all the sudden I start loosing power. Like I will be driving and I have my radio on, I use the turn signal, or the wipers or turn on the lights and it shuts my radio off and I sense and feel the loss of power. The other day I started my car up and it started funny, I sensed the same problem I've faced for last 6 months. I didn't turn my car off because I knew it probably wouldn't start after I turned it off. I had about 60 miles to drive. I drove the 60 miles and pulled in my driveway. I turned my car off and immediately tries starting it again. It was dead. This is the 4th altenator in 2 years. The one I have in now was brand new and has only been in the car for 5 months. The battery is good. I feel that I have a short somewhere or a bad ground but I have no idea where to start. The other day I had to replace one of my belts. As I was bending over to install the knew belt my stomach was touching the "V 6" logo on the front of the car and I could feel voltage and it felt like a Lil but of a shock. My car was off, so this tells me that I have a bad ground or a short somewhere. Anyone have any ideas? Also I can't hardly role up windows when this happens: (
Avatar
Lafeyette101
September 6, 2012.




How old is your battery?

Has anyone autopsied any of the failed generators to determine what failed? Are there any major engine oil leaks?


Caradiodoc
Sep 6, 2012.
Did you test the charging voltage? Was the harmonic balancer checked?


KHLow2008
Sep 6, 2012.
I do have a Lil bit of a leak on my valve covers but I went in and tightened them all yesterday.


Tiny
Lafeyette101
Sep 6, 2012.
A small leak shouldn't be a problem. Depending on the location of the starter and the generator, large leaks can cause oil to run inside them and deteriorate the brushes. They will soften and crumble very quickly. That's where the autopsy is of value. Repeat failure is less then six months is common.

If the battery is more than about two years old, it's "internal resistance" goes up. While it will crank the engine just fine, it loses its ability to dampen and absorb the voltage spikes that some generators produce. Those spikes can destroy the generator's internal diodes and voltage regulator. That has been a really huge issue for GM vehicles since the '88 model year but it can happen on any vehicle that has the voltage regulator built into the generator. To handle the control of the relatively high current for a transistor circuit, they use a "switch-mode" circuit which means the small current feeding the generator to make the magnetic field is turned full-on, then full-off hundreds of times per second. That is exactly how an ignition coil works, and a voltage spike is induced in that coil in the generator just like it's produced in the ignition coil. The difference is one is needed to fire the spark plugs and the other one is destructive. If you have another vehicle that needs a battery, consider putting the one from this vehicle in the other car and buying a new battery for this one.
AD


Caradiodoc
Sep 6, 2012.
Well I did a few things and then took it up to my friend that owns a shop. He checked the battery and the alternator. The alternator is not charging my battery. My friend recommended I get another alternator. That's fine I can take take off and put another alternator in, in less than an hour. It's just the fact of why every 6 months in having to put a new alternator in. I mean when I turn my headlights in everything else dims down a little, Evan with a new alternator. Ita just starting to eeek me. It's a great car and the only problems I have had is this. Around 6 months this happens. Its just getting old, I wish I could find out why I'm going through an altenator every 6 months


Tiny
Lafeyette101
Sep 7, 2012.
A bad harmonic damper would reduce the alternator output. If there is a fault with the main wire from the fuse box to the alternator, the altenator would be charging but the charge would not be getting to the batery.

If the new alternators you meant were rebuilts, not surprising to be replacing them every few months. If you have a lot of accessories, it is better to look for a higher output alternator.


KHLow2008
Sep 7, 2012.
I don't think a higher output unit is the answer. By their nature they can't develop more than their design current. They self regulate in that respect. Even if it's running wide open from lots of accessories, it should be able to handle that. If one diode overheats and shorts you'll lose exactly two thirds of the output capacity but it will still charge a little.

I discounted a slipping outer pulley on the harmonic balancer because each new generator works for six months. I think by now the pulley would have torn loose and fallen off or made noise. Should have been weak power steering too.

Back to my comment about the battery. It is not a problem related to good or bad. It's strictly an age thing. The GM vehicles have a lot of repeat generator failures that can be reduced by replacing the battery when it is as little as two years old. They still work perfectly fine and will not cause a problem in 1986 and older cars with the better generator design.

That wire between the generator and battery is a good suspect too but besides the connection itself, I'm guessing it goes through a bolted-in fuse in the under-hood fuse box. Check that the fuse bolts are tight. Even before you disturb them, with the engine running, measure the voltage on the generator's output terminal, then across the battery terminals. Those two voltages must be the same. If the voltage at the output terminal is significantly higher, there is a break in that circuit and the output current isn't getting back to the battery.


Caradiodoc
Sep 7, 2012.

AD