Toyota thought i was nuts.....i started to think i was nuts. but i could definitely hear a very soft hi-pitched hum in my engine bay. Tonight, I pulled the 7.5a "ALT-S" fuse in the engine bay fuse box and the hum stopped. Put it back in and it started again. I did the cs144 upgrade. Anyone have any idea what could be causing this??
Soft Hi-pitched Hum
- Thread starter psea17
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bettywhiteT4R_2015
New member
I just read somewhere that it may be linked to the battery maybe? So I’d looked into that just to be safe. I’ll tag the post I read on it below.
https://www.toyota-4runner.org/3601593-post3.html
https://www.toyota-4runner.org/3601593-post3.html
Last edited:
spartacus
Senior Member
The 7.5 at s fuse gets power when the ignition is turned on. Check the current at the battery if the alternator is under charging or over charging, could be the voltage regulator. or could be some thing minor like the belt or ground.
this is a brand new cs144 alternator. have measured voltage at bothe the alternator and thd battery. both look great w minimal voltage drop since im running 2awg betw them.
pulled the fuse, disconnected the battery and let sit overnight. even w ignition on, no buzz atm. cant start truck cuz im waiting for my radiator which i hope to have later today. will report back later.
id love to know the source of the hi pitched hum. very odd. is it an alarm of some sorts? guessing it's too quiet to be that.
... some days i just want to drive this damn truck off a cliff.
thanks for chiming in!
pulled the fuse, disconnected the battery and let sit overnight. even w ignition on, no buzz atm. cant start truck cuz im waiting for my radiator which i hope to have later today. will report back later.
id love to know the source of the hi pitched hum. very odd. is it an alarm of some sorts? guessing it's too quiet to be that.
... some days i just want to drive this damn truck off a cliff.
thanks for chiming in!
phattyduck
Elite Member
Constant or does it change with RPM or electrical load? It could be the alternator (bad diode, etc.).
-Charlie
-Charlie
19963.4lsr5
New member
I had that issue with the Denso Alt and it was a bad diode in the bridge.
But mine would get louder with more load and the charge voltage couldn’t keep up with the load increase. It could barely supply 15a at 13.0v.
It could just be the brushes are noisy. It it a new or reman Alt?
What is the battery post voltage when you have lights on and fan on max speed?
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But mine would get louder with more load and the charge voltage couldn’t keep up with the load increase. It could barely supply 15a at 13.0v.
It could just be the brushes are noisy. It it a new or reman Alt?
What is the battery post voltage when you have lights on and fan on max speed?
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19963.4lsr5
New member
DB electric sells new Alts. I bought a CS Alt for my Saturn a few years ago and have had zero problems so far. If I ever go that route for my Toy I was going to purchase a new one from them.
Yours being reman means you could find a local reman shop and have it gone over.
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