View Full Version : Alternator tech inspection help needed

09-20-2005, 10:58 AM
I suspect that the alternator on my FZJ80 is not doing its job well -- seems like I need to charge the battery using my trickle charger about once a month, and it's becoming more frequent. Questions:

1. How do I go about inspecting the alternator to find out if this is indeed the culprit of my problems?

2. I don't have a multimeter. Last time I was at Sears, the prices ranged from $10 to $200. What functions do I need on a regular basis? I prefer to buy good tools that will last a long time and be accurate, so if the $90 meter will perform more accurately and reliably than the $10 tool, I'd prefer to buy the good one. However, I don't want to spend $200!

3. If the alternator is the problem, can I rebuild it rather than replace it?


09-20-2005, 11:24 AM
I know a lot of people like to hate on Napa, but the one here in Louisville has always treated me right. You can drive your rig in there, and they can determine if it's likely a battery problem or not on the spot. If it's not a battery issue, you can bring the alternator in there and they can test that for you. At least that might save you some time determinging where the problem is.

As for re-building, I don't know. With past vehicles I've always just bought re-man. alternators and never had a problem with them.

Also don't know much about multi-meters. I use mine about once a year, and always have to re-acquaint myself with it.

09-20-2005, 01:32 PM
Matt if you plan on keep the 80 get a FSM that will walk you through all that stuff, also get the supplement Electrical manual. As for meters one with the Volts and the Ohms is the basic. Anything else if you do not know you may not want to know.
So with the VO meter on Volts, hook it to the battery. Read the volts with the truck off. Should be around 12.3-12.7 V. With the vechicle in idle should ve in the high 12(12.7 or so) to low 13. With it reved to about 1800-2000 should be in the 14-14.5V. So next is to turn on everything that draws current. Both at idle and at high idle (18-2000). It may come down but not much from the before recorded spec's. After turning off stuff and allowing the idle to come down, turn off vechicle and see what the voltage is and watch if it goes down fast or not at all.
If your alt is with in these ranges all is fine with it, then check your battery. I have found this to be more of a problem in toyotas then the alt.
Or do as the other matt says, take it in to see what is up. later robbie

09-21-2005, 05:13 PM
Matt, I wouldn't waste a lot of money on a fancy multimeter for automotive applications. The $10 ones I have been buying from Harbor Freight work just fine, and they're cheap enough that you can keep one in the glovebox of every vehicle like I do. And if you run it over or lose it, no big deal. They are plenty accurate for automotive work.

The description that Robbie gives above is the way I have been diagnosing bad alternators for 30 years, and has been 100% accurate. My experience is a bit different in that most vehicles that I have worked on will read 13.8 to 14.2 volts even at idle, provided the only load is the ignition system, however I have seen a few that were only in the mid 13s. Anything under 13.0 at idle means something's wrong. And as he suggested, turn on all your loads and see what you drop to.

An alternator has 3 internal diodes (rectifiers). One of the common failure modes is that these diodes fail, however I have seen a few cases where one or two fail but there is at least one or two good ones. When this happens, the alternator can not provide as much current as it is supposed to, so when you draw a fair amount of current, you're actually drawing it from the battery. That's why it's important to check voltage with loads being drawn. Most of the time, when an alternator is completely shot, the battery starts out at maybe 12.5V or so, then you start up and it drops down to 12.3 or 12.2 or so. This is the vehicle running on battery power only. Other, less common failure modes include partially shorted windings, mechanical failure, and worn brushes.

An inexpensive hygrometer can help you determine what kind of shape your battery is in. Most regular (non-optima) batteries only last 4-6 years, and they hold less and less of a charge as they age. While cold weather makes battery problems obvious due to increased internal impedance, it is high temperatures which wears them out. Overcharging exascerbates wear from high temperatures.

My offer to have an auto-related basic electronics class for the club, similar to Matt's GPS presentation, is still standing. We would need about an hour to cover the basics: ohms law, using multimeters, common auto electrical problems and diagnostic techniques.

09-21-2005, 09:03 PM
So...this is timely...I'm tracking a low-voltage gremlin in my 87FJ60. I've done the test as Jeff talks about and I'm in the lower range just about 13 at idle, if not a little lower. As an example, when at idle with just my headlights and radio on, my dash-meter reads just under 12 if I put everthing on, it reads closer to 10. Now...if I do the test with voltmeter...I pick up about a .5 to .75v. So, I'm sure the dash meter isn't totally accurate. I also have a toyota Re-man'd/re-wound alt that's pushing about 70A (had it tested). I'm thinking my lights shouldn't dim at stoplights.

How do you test the diodes? and if they check out, where do recommend starting the trouble shooting. I"m stumped after replacing all the battery/chassis grounds. I have the power cable to replace still...

Sorry for the hi-jack, and FWIW I'd really like to go through a electrical 'primer' like the upcoming GPS one.



09-22-2005, 12:22 AM
Cardinal, you should definitely be getting more juice with your loads on, unless your idle is really low. When you do the test, you should always rev the engine up to at least 1500 RPM to see the difference between idle RPM alt output, and full output. While most alternators produce full output at around 2500 RPM, in the real world there is only a minute difference at 1500 RPM.

There is no practical way to test the diodes without dismantling the alternator, however an alt with one diode failed will put out approximately 2/3 current, and with two out will put out about 1/3 current.

If you have a second car, most all parts stores will test your alternator output for you if you bring it in to them.

Do not overlook your wiring and connectors!

Both your 60 and Matt's 80 will have the solid state regulator integrated into the alternator; when they fail, they will usually fail catastrophically, unlike the electromechanic external regulators in the older models. However it is certainly possible that the regulator may be unable to pass sufficient current.

It should go without saying that your alternator belt needs to be properly tensioned. The easiest way to know that the belt is too loose is the squeal right after start up. Overtightening will wear out the bushings prematurely.

09-22-2005, 11:28 AM
My take:

1. How do I go about inspecting the alternator to find out if this is indeed the culprit of my problems? Detailed very well above. Napa can do it if you like, with a load test.

2. I don't have a multimeter. Last time I was at Sears, the prices ranged from $10 to $200. What functions do I need on a regular basis? I prefer to buy good tools that will last a long time and be accurate, so if the $90 meter will perform more accurately and reliably than the $10 tool, I'd prefer to buy the good one. However, I don't want to spend $200! Like Jeff says, you only need the most basic functions.

3. If the alternator is the problem, can I rebuild it rather than replace it? Yes, it's simple on a minitruck and I would expect it to be similar in an 80. I wrote this (http://www.4x4wire.com/toyota/tech/alternator/), which also covers replacing the brushes, a common issue and very inexpensive to replace. Not sure how much is directly comparable to FJ-land.

09-22-2005, 03:43 PM
Thanks for all the great info! I'm going to buy an inexpensive meter at Sears and get crackin'!

09-22-2005, 06:19 PM
Matt, if I'da thunk it last night, I would have simply given you one. I keep one in every glovebox, and still have a couple new-in-box at home. I've given about a half dozen away at RS raffles. You're welcome to a free one if you want it.

09-22-2005, 06:32 PM
Bad thing about early alternators for the curisers is that they require to solder in the brushes. They are a bit of a pain to play with. But if you are good with the iron, then it is just paintance. The Alternator in the 1fz 80 has replaceable brush holder like your mini truck. With the Manual you may be albe to find the full field hole to test(early alteranors, pre 1fz 80's) and see if the alternator is the problem or the regulator. By grounding the full field you then see if the alterator can produce the voltage or not. If it does not produce voltage, something wrong in the Alt, if produces voltage, then in the regulator (jsut replace it, carquest has them for around 100 bucks from japan). call me if you need a hand. later robbie

09-27-2005, 12:12 AM
OK, I think my problem may be something else...

This morning my 80 would not start after sitting all weekend. I put the trickle charger on it, and left it for the day. It was a very nice day for driving my topless 40 anyway.

I bought a $20 multimeter from Sears. Tonight I did some measurements:

Battery with vehicle off: 12.34 v
Battery with vehicle on, idling: 14.56 v
Battery with vehicle on, headlights on, car stereo blasting, A/C on super cold with fan blowing on high, idling: 14.55 v
So I'm thinking that my battery is probably OK (it's an Optima red top, only 1 year old). And I'm thinking that my alternator is doing its job. So something is probably drawing current when the vehicle is off, and now I need to discover what it is.

What next?

09-27-2005, 12:37 AM
Take that nice new multimeter, disconnect the red test lead from volts/ohms and connect it to amps. Set the range to 200mA. Disconect one of your battery leads. Connect the multimeter between the battery post and the disconnected lead. A current draw of a couple, maybe tens of milliamps will be normal draw from stereo clock, etc. Several hundred milliamps means trouble and could explain battery discharging while sitting. If current draw is normal, then your red top may be bad, not holding a charge. I have a yellow top which exhibited the same symptoms. Rare, but it happens. Less rare, you have a faulty load such as your ECU.

You certainly want to eliminate your battery cables as the source of the problem. I assume you jump start at the battery end of the battery cables. Usually, if the cables are bad, it won't start this way, but not always. Another good test is to prick the top of each battery post with your test leads while measuring voltage while an assistant cranks the engine. If the voltage drops very low, say under 11 volts or so, it is almost surely a faulty or discharged battery. You can repeat the test with the positive lead at the starter post and a chassis ground to see how much different it is due to voltage drop from the battery cables and associated connections. You shouldn't see more than a half volt or so difference.

At least you know your alternator is good. Those numbers are fairly typical, maybe even a little high. 13.8-14.2 is more what you want to see, but 14.5 shouldn't be too bad. Overcharging due to too high regulator output can shorten battery life greatly.

09-28-2005, 01:09 PM
Jeff, thanks. I'll work on this some tonight.

Three Wheel Ben
09-28-2005, 06:10 PM
Matt, one caution on checking the parasitic draw (amps) make sure everything is off and the key is out of the ignition. Dome light on = blown fuse in meter. No big deal, but you just have to hunt down another fuse. The spec from toyota is 40-45 milliamps or less with everything off.

ben :D