Experts' alternator/charging advice needed: Alt upgrade
 

Hi fellow 4Runnerers
Im trying to figure out what is the M terminal on the alternators on the newer 4Runners and Toyotas in general for, since I drive an older one that has no M terminal. I'll post this in the 5th gen too, since 4ths and 3rds dont have the M terminal.

What I want to do is upgrade my 4Runner's alternator to a higher AMP rating. The 4Runner I have is a 3rd gen purely mechanical diesel 4Runner and it originally comes with a 60amp alternator, that is sufficient for all the loads installed from the factory but... after having it for 10 years, I upgraded it with almost all stock options and extras from both the 4Runner and Hilux Surf and now Im starting to run on occasion into starter battery drain issues while driving.

The current regular winter wattage in the car is as much as the alt can provide in amps and not enough to charge the battery. And I haven't even turned ON the fog lights or use the wipers, heater seats, talk about turning ON my secondary crap like fridge and hf radio and charge my AUX battery all at the same time... It's only time until I drive 500kms and turn off the car and wont be able to start it because all the electrics and electronics have drained my starter during driving... :D :D :D

The alternators from the US gasoline engines are not bolt on and they are only 80amp max which is not enough. I know there are options to upgrade the alternator with a generic crap alts, but I prefer it to be calculated by Toyota and OEM quality.

I found a few options here that seem to have the correct mounting options for the 1KZ-T motor and seem to be able to fit by just changing the pulley on the alt itself. The amperage is 120 and 12v, which will be more than enough I think :D, and they are from cheaper Toyotas that I don't know why the hell they would need a 120 amp alts!

The quys in NZ and Ausies use the 1HD 120 amp alt on the 1KZ, but it needs a modded bracket for mounting it (not a big deal). But since it's a bigger alt, it will protrude more towards the frame horn and I already have an engine Webasto preheater (to heat up the cabin and keep the engine warm in winter trips) mounted on the frame horn and is about 2 inches away from the current alt, which is far enough not to rub against the engine at idle.

Another reason not to use the 1HD alts, is that junk yards here want too much money for a used and abused one, because they know it's for the legendary Cruiser!

The diagram is for 5th Gen 4RUnners charge circuit. The M terminals is connected to the ECU and if applicable to other electronics, in this case AC amplifier.

All I want to know is if anyone can confirm the M terminal's function. Is it to send a signal to the main ECU to inform it of it's working condition or is it for the ECU to send a signal to the alt for control?

Im thinking that if the M terminal is only to provide a signal to the ECU, than I have nothing to worry about electrically and can just replace my original connector with the new one, and rewire the engine harness.

But if the signal is mandatory, because the ECU controls the alt in some way, then I will have to research further since I have no engine ECU and have to find out what signal is sent to the alt.

Thanks
Pavel

From what I understand it’s a input to the ECU to tell it how much of a load it has.


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It is how the ecu monitors load output and of it falls under a certain threshold, the ecu will set a cel.

Thanks guys I was thinking the same thing. But since toyota puts arrows in their schematics indicating the direction of current travel between systems (not the diode arrow symbol), I was confused it might control the alternator somehow.

Like in this diagram of the 1KD motor which also has a 4 pin alternator connector, you can see that the arrow points towards the alt and has a description "From engine ECU", while current travels from the alternator to "To Daytime Running light relay" - arrow points away.

I did read that the M terminal on alternators mean "Monitor", but only in general pdfs and sites around the web, not official Toyota description.

I think that it is in fact a monitor function, but it acts differently. If the alternator fails due to a belt breaking, it will stop rotating and all lights on the dash will flash. That's how you tell that it's specifically an alternator problem. All those lights that turn ON at the same time have a diode that prevents them from getting current when the alternator is running. But when it stops, current stops pushing on the diodes and has less voltage than the battery the battery's current coming from the bulbs and goes to the alternator's regulator that leads them to ground (when not energized) and that's how all those bulbs turn ON.

I might think that it might be the same thing with the M terminal. If the alt fails, the ECU, sending current to the alternator, will also get to ground and will know that the alt failed, and i think it might switch to limp mode, especially if the alternator belt is also running the water pump.

But if that's the case, why would they put a separate pin on the alternator instead of just connecting it to the same circuit that the bulbs are connected to? I dont know...

What do you think?

Thanks
Pavel

I think you have a better understanding of the alternator circuit function then me. Hopefully some one with more knowledge can jump in.

Let's get the other connections defined for the rest of the audience:

B: Main power output from the alternator (bolt-on connection)
S: Sense voltage return to the alternator - used to make sure the battery charge voltage is correct at the battery itself.
IG: Ignition power, this is the 'excite' signal that turns on the alternator and allows it to output power on the "B" terminal
L: Charge warning light output. Pulls to ground through the alternator when the alternator senses a problem internally.
M: Let's figure this one out...

First, a document directly from Denso: https://www.denso.ua/media/815126/16...web_locked.pdf

Page 52 indicates that the "M" terminal is a duty cycle output that mirrors the output demands on the alternator. There is also mention of a return control signal that can also be present to request different output voltages depending on conditions programmed in the engine ECU (I know some Honda alternators support this feature).

Here's a general link that corroborates: Regulator Terminals - What Do They Mean? - Professional Motor Mechanic

So, my guess is that you can leave that terminal disconnected with no ill effects.

-Charlie

Pure thanks guys!
That pdf is saved to my Toyota database!!!! Very helpful!
So I ordered one unit from the shady junkyard, and asked for the connector also, so I dont have to play around trying to make my own.

Once it arrives, I will document everything and let you guys know how it turned out, if of course the enclosure is not too different from my original alt.

So wish me luck and have a good afternoon! I am going to sleep since it's like 11pm here!