Kawi2strokes.com Forum

I have a weird one here. 1991 toyota pickup with a v6. Start truck drive around and everything is fine. I make a stop at the store, turn the truck off. When I restart it, the dash lights are on(to indicate alternator not charging) and the alternator isn't charging. When the lights are off I am getting 14.3 volts at the battery with it running. When they are on, I was getting between 10-12 volts on the alternator lug(12.? at the battery). What is causing this not to charge after a restart? If it sits long enough then all is fine. I didn't really want to put an alternator on if it is something simple.

It sounds like there is a connection getting warm and going to a high resistance during operation somewhere. Have a look at the connections of the battery and clean both terminals and inspect the cables. Also check the battery ground cable (especially the smaller lead where it bolts to the body , if it has one).

The connections at the alternator and or wiring could be corroded/partially broken too...

Does the truck have an external regulator? If so, the wiring here could be corroded/broken too or the regulator is faulty....

Other than the above the alternator itself could be failing from sticking/worn contaminated brushes/ failing diode pack/internal fault of stator or field windings that shows up with time/heat

J

I am pretty sure the alternator has the regulator built in. It does sound like a heat issue, but it is weird that it only does it after it is turned off then re-started. You would think that there is the same heat there before it gets turned off as after it gets restarted. The main lug on the alternator doesn't have any visable corrosion, I will need to check the plug. The battery terminals don't look so hot, but they have been like that for years. I did hit them with some baking soda the other day, but I sould take them off and clean as well.

That looks more and more to main battery terminal connections. The high load imposed by the starter will alter a bad connection....

J

If the battery terminals were the culprit, would you still see a loss of voltage from the lug on the back of the alternator when the malfunction lights are on?

I'm not one that's able to give advise on electrical issues... LC can attest to that!
But I once had a fried ignition switch that caused odd behavior before it finally let go.

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Upon second look at your snag the problem is likely in the cable that is connected to the alternator output lug. I state this because you posted above when the problem occurs voltage at the alternator is less than the battery. The heavy lead in question on the alternator connects essentially directly to the + terminal of the battery, hence should always have the same exact voltage as measured at the battery.

This also comes back to proper battery terminal connections. If there is a bad connection here the alternator will have less than optimal power supplied to it to excite its field.

Just remember the alternator must be supplied power (a clean battery voltage) for it to make power.....

The alternator may also rely on its case to ground it. Are the mounts clean?

J

This too is possible as iggy switches do wear out! If Toy. has run a separate field supply and reference voltage wires to power the field the ignition switch could cause an issue like this.....

There is still the matter of the differing voltages measured at the alternator main output and battery.....

Do you have a wiring diagram of the charging system. If so you should be able to meter the alternator wires and find what value is not right.

J

Can you make this malfunction occur repeatedly?
Easy enough to eliminate bad ground possibilities by running a temporary ground from alternator to battery.
The good news is that it most probably limited to only 3 things:
Switch, alternator (to include regulator), or wiring

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No. . It did happen today on cold startup though. I have been doing some internet surfing on the topic and it looks like the brushes go in the ND alternators with high miles. They are easily servicable with a drop in kit from the dealer or seperate solder in brushes from the aftermarket. From what I have read it should fix my problem. For the $8-$20(depending what I can get from where) I am going to give it a gamble, better that the $120 for a rebuilt alternator. If it fixes it great, if not I am not out very much time or money.