Power issues, possible alternator problems?

D

doublezer6

New member
Have a 1991 4runner, recently was on long drive and noticed the battery level gauge slowly dropping. As was doing so, the emergency brake light came on, then the battery symbol lit up, then my radio turned off, then the anti-lock brake light turned on, then the whole car died while I was pulling over. Was able to jump start the truck shortly after, made it about another 10 miles, then died again following same process as before.

Battery was old so just replaced with brand new battery thinking bad battery might be the issue, managed to make it the 60 some odd miles back home, but same series of events as above happened again and the truck died again right as I was pulling into my driveway.

Pretty sure this is evidence that I need to replace my alternator. Thoughts or suggestions before I dive into replacing the alternator?
 
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Throw a multimeter on your battery terminals to be sure. With vehicle idling a healthy alternator should be putting out between 14.0 and 14.6 volts...If your in the 12's you're running off the battery only...
 
Signs point towards alternator.. but please be sure to check grounds all around the block. A bad/loose ground can really throw some weird symptoms.
 
brake and battery lights simultaneously is common when you lose an alt belt or the alt is not charging any more.

Take it down and have your local parts store check to see if its working on their alternator testing machine.

Not sure if this is 4 or 6 cylinder, there's lots of writeups about alternative replacement alternators if you'd like to have a bit more amperage if you need to replace the stock unit.

Other than that, do as the others have said, check all the ground points as well as the ~8gauge +12vdc wire from the battery to the alternator. That can also be falling apart and cause the alternator to waste most of its output to heat through that wire if its corroded or falling apart. If it is, that's an easy one to repair, search a bit around for "big three upgrade", that will help you replace a few wires and gain a few extra amps of current.
 
doublezer6 said:
Have a 1991 4runner, recently was on long drive and noticed the battery level gauge slowly dropping. As was doing so, the emergency brake light came on, then the battery symbol lit up, then my radio turned off, then the anti-lock brake light turned on, then the whole car died while I was pulling over. Was able to jump start the truck shortly after, made it about another 10 miles, then died again following same process as before.

Battery was old so just replaced with brand new battery thinking bad battery might be the issue, managed to make it the 60 some odd miles back home, but same series of events as above happened again and the truck died again right as I was pulling into my driveway.

Pretty sure this is evidence that I need to replace my alternator. Thoughts or suggestions before I dive into replacing the alternator?
Click to expand...


To me it sounds like a real safe bet that you have a dead alt. If you dont have a multimeter you can get your truck runner and pull the ground off the battery if it dies you need an alt. if not then maybe a voltage regulator.
 
All of the above, although I would not feel safe disconnecting ANY battery cable while truck is running.

IF 22R-E, here's how it works with voltage test points and readings.

Yes, it could be alternator, so have it tested.
Yes, it could be wiring.


IF you could not have it tested right away and IF you are confident enough...

Maybe alternator is not getting excitation through IG wire?
IF you can safely hold a probe to the back of the alt connector into the IG pin, check for 12V while truck is running.
OR:
(1) Temporarily remove connector from back of alt,
(2) Use 1/4-inch spade terminals to connect "S" pin (thin white) and "IG" pins (thin red wire) directly to battery.
(Don't worry about "L" (yellow wire), yet
(3) Run truck and make voltage measurements at Screw terminal of alt
(4) Measure voltage on battery post

Voltage at alt output should be within range in link above. If not, alt is bad (or its regulator).

IF voltage at alt output is good but battery connector and/or post is not the same, "B" wire could be bad.
 
RAD4Runner said:
All of the above, although I would not feel safe disconnecting ANY battery cable while truck is running.

IF 22R-E, here's how it works with voltage test points and readings.

Yes, it could be alternator, so have it tested.
Yes, it could be wiring.


IF you could not have it tested right away and IF you are confident enough...

Maybe alternator is not getting excitation through IG wire?
IF you can safely hold a probe to the back of the alt connector into the IG pin, check for 12V while truck is running.
OR:
(1) Temporarily remove connector from back of alt,
(2) Use 1/4-inch spade terminals to connect "S" pin (thin white) and "IG" pins (thin red wire) directly to battery.
(Don't worry about "L" (yellow wire), yet
(3) Run truck and make voltage measurements at Screw terminal of alt
(4) Measure voltage on battery post

Voltage at alt output should be within range in link above. If not, alt is bad (or its regulator).

IF voltage at alt output is good but battery connector and/or post is not the same, "B" wire could be bad.
Click to expand...

Actually your real safe pulling the battery cable as long as you pay attention and dont put your hand in the radiator fan or touch the cable to anything i do it all the time and have never had a problem (knock knock)
 
You really should be careful doing that, as the alternator without a battery will allow voltage spikes nearing 16-18 volts, depending on the rpm of the engine.

The battery acts as a sort of capacitor in the system, which allows the alternator's regulator to apply steady voltage to the system. Without the battery, you'll probably notice that the lights will get noticeably brighter without a battery installed, and will get really bright if you rev the engine.

Not good for lamps, but extremely bad for the ecu and any car stereo equipment you have installed!

Watched a friend blow a whole bunch of stuff out on a relatively brand new 88 or 87 Dodge Shelby Charger when he disconnected the battery's positive terminal while it was running. I believe he ended up with new headlights, taillamps and a few dash bulbs after that error! Don't ask me why he pulled it off though, possibility the battery was dead and he pulled it off after jumping the car or maybe it was still stuck to the jumper cables or something. Way too long ago for me to remember details!!!
 
Have just now gotten around to looking into this. This one is a V6. It wouldn't start on its own but the battery seemed fully charged as all lights, headlights, radio, etc. were working. Jumped it successfully and tested voltage with a multi-meter before and after and it was hovering just below 12v.

Thinking all signs point to new alternator. Pretty sure its the original alternator and milage is about right for replacement time.

Thanks very much for all the help so far!
 
Another thing to check is the fuse for the alternator. I had an issue like this on a customer's truck when I was a car mechanic. Changed the alternator because it tested bad with a basic tester. Ran fine for about 30 minutes then battery light again. Customer changed battery (under warranty, as toast) and then same thing. Came back and I did a little diag to find the fuse for the alt was blown. Make sure to check the cheap things (fuse) before changing out that alternator. Just a good general practice thing that could save you some time and money.
 
After jumping it, once you disconnected the jumper cables, did the brake and battery lights come back on?

Should have been pretty immediate, since you were seeing below 12V. I'd check the fusible link (or fuse if it has that, not sure when toyota moved to fuses) like the last poster suggested.

Also, take the alternator in to the parts store, could just be the regulator's gone out. Much cheaper to replace the regulator than the whole alternator! Ebay shows them at about 25 bucks, vs. a new alternator at $160!

I believe the denso part number for yours is Denso 126000-0610, on Amazon for 28 bucks. Double check that part number though, don't know which alt. was put in your vehicle.
 
Had the alternator tested and sure enough came back as bad. Put in new alternator and the truck fired right up. Only now, there is a squealing noise when its running. Could this be a symptom of the belt being too loose or tight?

Also, I just started it and let it run idle for a few minutes to make sure I had everything connected right, but when I read the voltage on the battery it was still coming in at just under 12v. Should this immediately be reading closer to the 14v mark or...? When I tried to start the truck again this morning it wouldn't start, but all the lights, radio, etc, were working (back to square one). Does the battery just need some time with the car running to get back up to par or...?
 
Check your belt if its squealing and you're not getting any current to the battery!

Do a youtube search for measure belt tension, that should show you how to test the belt for the proper deflection. Me? I just twist the belt with my fingers, if I can twist it more than a quarter turn, its too loose, if I can barely twist it, its too tight.

If you're squealing, its definitely too loose.
 
A neighbor with a little know-how helped me to tighten the belt better than I could and all works wonderfully now. Thanks to everyone for the help.
 
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