$900 94 Rodeo alternator issue

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$900 94 Rodeo alternator issue

Postby fantasoap » Thu Dec 08, 2016 12:53 am

Hello and thanks in advance... I'm inexperienced with electrical systems.

Patient facts:
1994 Isuzu Rodeo, 200,000 miles, 6 cylinder engine, 2wd, purchased by current owner for $900 in September 2015.

October 2016-After slamming my hood shut with needless force, I started the car and began driving, but I soon noticed that the dashboard voltmeter had dropped from its normal 13 volts to below 12 volts. I proceeded to hurry home before the battery died, as I assumed this meant that the alternator was no longer generating current.

On the way, as the voltmeter steadily dropped, several idiot lights came on (the brake warning light and two others which I don't remember). I continued driving.

About halfway home, I hit a pothole.

Eureka! The voltmeter jumped back to about 13 and the idiot lights all went out.

I did not investigate the matter further.


December 2016-Though I did not slam the hood again, the scenario repeated itself exactly, except that this time the battery drained down, the car stopped running, and I called a tow truck.


To me, it sounds like a loose wire, because of the jarring that initially caused the alternator to stop charging the battery, and the subsequent bump that seemed to fix the problem, but I am not sure about how to locate the broken connection. My dad suggested that the engine block ground strap might be loose, corroded, or severed, but I am not sure where it is located. I have been looking for an uninsulated, flat braided cable roughly 15 mm wide, but all have found is an insulated wire about 2 mm in diameter connecting the cylinder block to the sheetmetal on the North American passenger-side of the engine.

I really appreciate any ideas people have, and suggestions as to necessary tools and reference documents would be extremely useful. Thanks!
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Re: $900 94 Rodeo alternator issue

Postby Carl747 » Thu Dec 08, 2016 2:13 pm

I had a problem with my Trooper that was not the same, but similar. When it was finally taken into the mechanic the problem was that a bad battery terminal was causing the battery to arc and lose charge. It sounds like you have a similar problem or a wiring problem. I would take it to Auto Zone or a similar place where they will test your alternator free of charge and see what they have to say before you take it to a mechanic.

Here is a more in depth explanation of the problem I had if you are interested:
http://www.planetisuzoo.com/viewtopic.php?f=7&t=95073
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Re: $900 94 Rodeo alternator issue

Postby fantasoap » Sat Dec 10, 2016 5:46 am

Carl747 wrote:I had a problem with my Trooper that was not the same, but similar. When it was finally taken into the mechanic the problem was that a bad battery terminal was causing the battery to arc and lose charge. It sounds like you have a similar problem or a wiring problem. I would take it to Auto Zone or a similar place where they will test your alternator free of charge and see what they have to say before you take it to a mechanic.

Here is a more in depth explanation of the problem I had if you are interested:
http://www.planetisuzoo.com/viewtopic.php?f=7&t=95073


Thanks for the advice!
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Re: $900 94 Rodeo alternator issue

Postby batvette » Sun Dec 11, 2016 9:32 am

fantasoap wrote:
Carl747 wrote:I had a problem with my Trooper that was not the same, but similar. When it was finally taken into the mechanic the problem was that a bad battery terminal was causing the battery to arc and lose charge. It sounds like you have a similar problem or a wiring problem. I would take it to Auto Zone or a similar place where they will test your alternator free of charge and see what they have to say before you take it to a mechanic.

Here is a more in depth explanation of the problem I had if you are interested:
http://www.planetisuzoo.com/viewtopic.php?f=7&t=95073


Thanks for the advice!


Intermittent open circuits can be tough to diagnose. I would disconnect your negative battery cable and go over all the connections in your charge system starting at the alternator, then the underhood fuse box etc. If in doubt about that ground strap add another..you may want to do it by the book with a schematic.
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Re: $900 94 Rodeo alternator issue

Postby fantasoap » Fri Dec 23, 2016 12:55 pm

Thanks for the input!
Where would you go for schematics and factory repair manuals?
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Re: $900 94 Rodeo alternator issue

Postby QuantumRift » Sat Dec 24, 2016 12:27 am

Just about any of us have schematics to scan and post for you. But yes, a corroded and loose connection can play havoc with your sanity.

Definitely check ALL the alternator wires and connections for tightness and corrosion.

Has the ignition switch ever been changed or checked. I ask because many many years ago I ran into a similar problem with a Ford and bad igniton switch. Bad conections, and a heavy key fob caused the engine and charging system to go a bit nuts on bumpy roads. Wasn't my car, but a friend's car. When he drove it, no problem. When his wife drove it, problems because she had a BIG heavily loaded key fob that caused ignitions switch problems....just a thought.
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Re: $900 94 Rodeo alternator issue

Postby gb89amigo » Sat Dec 24, 2016 6:38 pm

fantasoap wrote:Hello and thanks in advance... I'm inexperienced with electrical systems.

Patient facts:
1994 Isuzu Rodeo, 200,000 miles, 6 cylinder engine, 2wd, purchased by current owner for $900 in September 2015.

October 2016-After slamming my hood shut with needless force, I started the car and began driving, but I soon noticed that the dashboard voltmeter had dropped from its normal 13 volts to below 12 volts. I proceeded to hurry home before the battery died, as I assumed this meant that the alternator was no longer generating current.

On the way, as the voltmeter steadily dropped, several idiot lights came on (the brake warning light and two others which I don't remember). I continued driving.

About halfway home, I hit a pothole.

Eureka! The voltmeter jumped back to about 13 and the idiot lights all went out.

I did not investigate the matter further.


December 2016-Though I did not slam the hood again, the scenario repeated itself exactly, except that this time the battery drained down, the car stopped running, and I called a tow truck.


To me, it sounds like a loose wire, because of the jarring that initially caused the alternator to stop charging the battery, and the subsequent bump that seemed to fix the problem, but I am not sure about how to locate the broken connection. My dad suggested that the engine block ground strap might be loose, corroded, or severed, but I am not sure where it is located. I have been looking for an uninsulated, flat braided cable roughly 15 mm wide, but all have found is an insulated wire about 2 mm in diameter connecting the cylinder block to the sheetmetal on the North American passenger-side of the engine.

I really appreciate any ideas people have, and suggestions as to necessary tools and reference documents would be extremely useful. Thanks!


As far as factory manuals go, you have to troll eBay and Amazon on a regular basis. Otherwise could try: http://www.reliable-store.com/products/ ... ice-manual or http://www.reliable-store.com/products/ ... hop-manual

Have not tried them myself, but looks good! Best of luck,

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Re: $900 94 Rodeo alternator issue

Postby fantasoap » Sun Jan 01, 2017 6:15 pm

Thanks everyone for your support!
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Re: $900 94 Rodeo alternator issue

Postby fantasoap » Thu Jan 05, 2017 2:22 pm

Hi
I took the alternator to O'Reilly's. They say it's good.

There's a blue relay under the hood, labeled "Charge". According to the wiring diagram (attached) it illuminates the charge warning light if the alternator is not charging the battery.

I believe I have narrowed the problem down to this relay, but, logically, I am not sure that it has any influence on the actual charging of the battery. The diagram is confusing on that point.

I do not understand why there are five terminals on the relay instead of four.

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Re: $900 94 Rodeo alternator issue

Postby fantasoap » Wed Jan 11, 2017 9:07 pm

The charge relay was faulty. Replacing it solved the problem.

I still don't know why it solved the problem, because I don't understand how the relay is actively involved in the charging process. I understand that it illuminates the battery light if there is no current coming from the alternator, but I don't understand the function of the circuit it switches to when the alternator is acting normally. Does anybody know how this works?
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Re: $900 94 Rodeo alternator issue

Postby gwana66 » Wed Jan 25, 2017 11:54 am

The relay and lamp provide the "exciter circuit" for the alternator. Newer alternators are self-exciting, but the older circuits need a small current applied to them before they will start charging. It's often done through the charge light. When the alternator is not outputting current, the relay is open and the light goes to ground through the 10A fuse. This also sends current to the alternator through the control side of the relay down the blue/white wire. Once the alternator starts producing a charge, it energizes the control side of the relay and closes it, interrupting the ground for the light - the light goes out. The alternator now supplies its own current until it stops turning again and the relay opens. If the alternator fails, the relay opens and the light comes on, letting you know. Consequently, if the charge light bulb burns out, the circuit won't work and you may not know until the battery dies. Usually revving the engine will excite the alternator enough to begin charging at some point, but it's an issue at idle. You can just send 12V from the ignition circuit to excite the alternator, but it's a better design to have it through the idiot light.
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