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2001 Ford Focus SE Sedan, 5 speed manual Cold Air intake, and some high mileage....
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Discussion Starter #1
Hey all,

I don't like how the PCM regulates my alternator to 12.9-13.5 volts all the time (Especially when I'm bumpin my system)

I understand that these alternators are PWM by the PCM along with an internal regulator for failsafe purposes. Well I had to wire a new connector in for the alt but when I did I had the 12v reference and the PCM+ Wire backwards and noticed that it practically full fielded the alternator (15.3 volts and probably about 250 amps from the aftermarket alternator).

That got me thinking, could you theoretically put resistors inline and step the 12v down to the PWM voltage?

Just an idea that I wanted to get some insight and opinions on.

Thanks!
 

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The regulator won't be able to read it, it is looking for pulsed duty cycle input there, it doesn't just read volts. And there is no one PWM 'volt' anyway, it has to change all over the map depending on the load. The PCM will log error as soon as it detects it can't change the voltage.

The regulator is NOT a failsafe, it is actually regulating at all times, based on the signal sent to it by PCM.
 

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2001 Ford Focus SE Sedan, 5 speed manual Cold Air intake, and some high mileage....
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Discussion Starter #3
L
The regulator won't be able to read it, it is looking for pulsed duty cycle input there, it doesn't just read volts. And there is no one PWM 'volt' anyway, it has to change all over the map depending on the load.
I understand that, I was more asking the voltage range, like does it use the standard signal voltage range of 0-5 volts. Like if I hook it up to the signal wire on my crank sensor would it read it as "Hey the PCM is commanding me to actually work"?

On the thought of simulating PWM could I theoretically use an old timing light and wire the light signal to the PCM + and simulate the width modulation?

Obviously the computer will get mad that it can't control something lol

I do think I need to look into getting a scope though, might make it easier to figure this out myself.

Why can't I just get a single wire conversion and call it good 😭
 

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I just told you volts are not being used there and again you ask about volts. What part do you not get? Your 'standard voltage range' of 0-5 is misplaced, there is nothing like that there at all. You are wildly confusing reference volts with PWM.

'Like if I hook it up to the signal wire on my crank sensor would it read it as "Hey the PCM is commanding me to actually work"?'

You do not understand the crank sensor either, it is a standalone signal maker.

'I theoretically use an old timing light...'

Nope, you say you understand PWM but you obviously don't. I suggest you study it closer. Timing light cannot reproduce different duty cycles.
 

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2001 Ford Focus SE Sedan, 5 speed manual Cold Air intake, and some high mileage....
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Discussion Starter #5 (Edited)
-PWM has no voltage
Uhh okay Noted...

What exactly does the PCM use to make the PWM then? Magic?

The way it controls stuff is the length of the pulse, so yea...

Crank sensor uses a magnet to generate signal, which is then sent back to the PCM in the form of low voltage no?

The timing light was a really simple idea because my thought process was it uses the field generated from the #1 sparkplug wire to signal the light on and off, so if we stepped that down to control voltage levels it would act like the PCM sending the signal, (Except just a single pulse that's not made longer or shorter) that's why I thought it might work, but that got shot down 🤷‍♂️

This is kinda why I came to the forum, bounce some ideas around, get some insight cuz I don't know exactly how this whole system works but eh...
 

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You got it right, the timing light signal would not change in length. Thinking the speed is same as home ac, or 60Hz. Speed stays the same, the length of the pulse changes.

Your idea of crank sensor is now right also. Very low volt though, if you even sent one volt from PCM to it it would likely blow out. Normal pulse there maybe 1/100 volt. Self-generating, Ford does not use Hall effect like others can. Ther difference is 2 wires needed vs. 3.
 

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2001 Ford Focus SE Sedan, 5 speed manual Cold Air intake, and some high mileage....
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Discussion Starter #7
So in theory, I could get a PWM motor controller and use that to simulate duty cycle from the PCM? Or will a motor controller use a different frequency range than the PCM?

I know I'll get an error code that'll light up my battery light if I disconnect the alternator from the PCM. But will it turn on my engine light?

Sorry if my questions sound dumb I'm just legitimately trying to find a solution that might actually work...
 

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Depends on your location state inspection laws. Some don't care about engine light but most do. If like Texas they can even refuse to inspect over battery light as it IS a safety aspect of a sort, the car can strand possibly at any minute. Here they allow inspectors latitude to step out of the normal inspection envelope if they feel something is wrong.

You should know the PCM also uses the PWM to let the regulators cool. When they charge steady they overheat and then they have to back way off charging or the regulator fries. A real risk if you go to constant charging. The OEM regulators overheat easy as spit.
 

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2001 Ford Focus SE Sedan, 5 speed manual Cold Air intake, and some high mileage....
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Discussion Starter #9
Well I just ordered an ebay Pulse width generator... I'll let ya know how that goes when I get it and hook it up.

I'll keep the overheat warning in mind, Do you think a decent aftermarket high output would overheat as easy as a stock one?

Actually now thinking about it that could've been why my oem alternator tried to catch fire on me... The 12v reference and the PCM+ got melted together on my exhaust manifold but I didn't notice it until I smelt the alternator burning and had charging problems (Part of the reason I just got a whole new connector for it)
 

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Why try to control the alternator that way? Sounds convoluted.
It’d be easier to just rewire for the older regulators that use voltage sense.
& have the ECM reflashed to bypass the alternator com lines?
 

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13.5V sounds like something isn’t correct.
System should be putting out 13.6 minimum with lights & A/C fan on high with a stock alternator.
 

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2001 Ford Focus SE Sedan, 5 speed manual Cold Air intake, and some high mileage....
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Discussion Starter #12
Stock alternator with new wiring to the control plug and an upgraded main power wire was putting out 13.0v with led lights all around and ac on full blast, not bumpin my 2 12" subs.

Even with the aftermarket high output it's getting regulated to 13.0v under the same conditions...

I wish I could just simply rewire it to use voltage sense, the only way you could is if you left it unplugged and it defaulted to 13.8v but it would still do the same thing under a the same load. (Believe me I've tried...)

Anyways that's not the main concern atm, I dropped a valve seat yesterday. Shattered the #4 piston and put a hole in my cylinder wall... Just picked up a short block and ordered a head that has the valve seat issue corrected. It only took 238k till it happened at least lol
 

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13.0V is a sign of ether a crap alternator or a problem with your alternator’s wiring setup/pigtails.
Did you add a ground wire to the alternator’s body to Batt. ground?
This is usually overlooked when improving the alternator to Batt. positive connection.

Also, have the alternator tested, consecutively 3X. The test can push an alternator to showing it’s true colors.
———
There’s some aftermarket alternators that actually have low charge levels at idle RPM’s & those places use the interstate RPM speeds for their amperage ratings. So in truth, your aftermarket alternator might be only putting out the rated amperage at interstate RPM.
 

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2001 Ford Focus SE Sedan, 5 speed manual Cold Air intake, and some high mileage....
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Discussion Starter #14
Yea I added a second 4 gauge ground to the alternator bolts I know it's not a ground issue cuz I also added a 4 gauge ground to the body and put the PCM grounds directly on that ground as well.

I suspected the alt was bad and I had it tested, it tested good consecutively.

During the day when I just have the windows down, no ac, it charges at 14v fine. But as soon as my ac goes on it doesn't charge over 13.2v at idle. But you're probably right about the interstate rpm thing cause cruising it tends to jump around the 12.8-13.6 range cruising.

Yea in my last post I should've specified that sitting at idle it doesn't like going above 13.0v at night with lights and ac on, my bad
 

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2001 Ford Focus SE Sedan, 5 speed manual Cold Air intake, and some high mileage....
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Discussion Starter #15
Okay so update!

She's back together and running better than ever! I got the eBay PWM Controller and my theory is correct! The alternator likes 125Hz and as I adjust the duty cycle on the controller it also starts charging the battery more.

Now to deal with the battery light...
I ordered some diodes and plan on putting those behind where I patch the controller into(Between the PCM and behind the Controller wires) and I'll have the controller on a switch so when I wanna stop and bump my system a bit I just flip the switch and boom, 14.6 volts of bumpin powa!

I'll post another update once I get the diodes and let ya know if it works to shut the battery light off.
Thanks people!


 
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