97 4Runner Electrical problem

My 1997 4Runner with 203,000 miles has begun exhibiting a strange problem that seems to be electrical. While driving the engine stumbles, the brake light on the dash comes on, then in most cases the engine catches again, the brake light goes out and I drive on. So far it has never actually stalled the engine entirely, but I've lost power to a dangerous extent. Often this happens two, three, as many as six times in succession before it seems to clear. I've noticed a high-pitched small motor bearing noise from under the hood at about the same time, as though a bearing in perhaps an alternator or other similar sized unit is wearing out. Ok, I understand it is an old enough truck that any of these things could be normal wear and tear, but it is Christmas, and a long weekend till I might get a chance to have diag codes read. I'm not even sure anything will have registered. I am most puzzled by the clear connection between the brake light and the apparent electrical problem.

Any ideas I might look at tomorrow, any hope that the brake light indicator is just an indicator that some code is being logged?

Thanks, Jere

Reply to
JMc
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alternator or

apparent

When I had an alternator problem in my '87 PU the brake light and alternator (charge) light both came on. Does the charge light come on when you turn the key prior to starting the engine? Maybe the bulb is burned out?

How long has it been since the alternator was replaced? 203,000 miles is a long time for the original to last.

FWIW, I had the alternator freeze up in a Chevy Lumina while doing 6o mph. It stopped the engine completely and I slid off of the highway. I was just outside of a small town and had some of my tools with me. So I took off the serpentine belt and drove it to the only garage for miles around.

Reply to
Anyolmouse

Thanks for suggestions: The alternator is original, (as is everything else but fluids, tires, brake pads and the throttle positioning sensor). Charge indicator does illuminate when I turn key on before starting, but has not yet ever lit during one of my episodes. I'll stay off highways and below 60 till I sort this out. Fortunately, it is manual trans and I can control potential skidding with application of clutch. I'll give an update after some more thought and investigation tomorrow.

Thanks again

Reply to
JMc

Do you have the optional 4 wheel brake equalizer gadgetry, AntiLock, or whatever they call it? "Brake Light" makes ME think BRAKES! I never liked the looks of all that plumbing...

Or... the optional automatic locking, i.e., vacuum operated, front differential comes to mind. Another plumber's bad dream.

Check your wiring, including grounds?

Yea, I dread those unpredictable power-drops in the middle of nowhere!

Take care, and Good Luck!

Reply to
Jeff

I do ABS brakes, though they are factory. But you raise a good point. I am now thinking the Brake light on the dash is a result rather than a source indicator. My sense is the electrical interruption is long enough for the ABS circuitry to sense and it is lighting the dash light to indicate they are not ready for emergency stopping.

I am back to tracing the electrical feeds from battery, alternator, starter and ground. It's pouring rain, melting our snow pack, and even a dry garage is not a comfortable place for crawling around, but better than a ditch somewhere.

Thanks, Jere

Reply to
JMc

Your reasoning appears sound. Of course, this is the type of problem that may not reappear, leaving you clueless as to whether all the fooling around did any good or not. And, you're probably inadvertently erasing any codes. But, what else can you do? How much more trouble would it have been to include OBDII scan and clear functions in the operating controls of the vehicle (not requiring the acquisition and use of a scan tool)?

I say optional ABS, since my '98 Tacoma does NOT have ABS, nor the automatic locking front differential. 4Runners may have had ABS standard.

Does the ABS c> I do ABS brakes, though they are factory. But you raise a good point.

Reply to
Jeff

There are no codes logged or pending. As an intermittent, it has been very difficult to diagnose, but my brother on holiday visit is convinced it is a crankshaft position sensor. He tells me it is a perfect symptom match on the interruption of ignition, and very easily can explain trouble starting. We (ok he) is not exactly sure of the high-pitch bearing noise, and unfortunately that has not exhibited itself this week. I'll run a tank of gas through after replacement and report back if anyone is interested.

Jere

Reply to
JMc

Feels like I can confidently confirm the Crankshaft Positioning Sensor was the source of this problem. A little more obscure than I expected, but at

203k miles, just about anything could be wearing out. This was not cheap, hope to get another 50k miles now.

Jere

Reply to
JMc

Thanks for the update! I wonder if a (more readily available) sensor might interchange. A Tacoma is rare in the upullit yards, but a Camry or Lexus are there for the picking.

NO error codes! Damn! Any more screaming?

JMc wrote:

Reply to
Jeff

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