PCM controlled alternator behavior question

[Fast4.7]

Anyone else with a P01/P59 and PCM controlled alternator experience a charging system cutout above ~5,000 rpm? It is so consistent at that RPM I feel it has to be the PCM cutting the alternator at high rpm. First noticed it passing on a 2-lane road at night. The headlights momentarily blinked dimmer while I was passing a car that felt like speeding up 20 mph while I was trying to overtake them. I already had the ~500 hp 383 in my Express van with the pedal on the floorboard, wrapped up in 2nd gear and went around them anyway. I looked all over the PIDs and have not found the alternator field coil duty cycle to datalog what is going on. Only concerned because I have heard of guys nuking their AD244 from over spinning them. I am only at 5,500 rpm on a WOT upshift and have the stock L31 belt ratio on the alternator. That is only 1,200 rpm on the alternator higher than the stock shift point at 5,100 rpm and with a ~3:1 belt ratio the alternator rotor rpm calculates out to be under the generally accepted maximum RPM for the unit. Has me scratching my head a bit. It is a 10 year old Napa 200 amp AD244 but seems to work great other than the high rpm charging cutout. If it were a normal cheap alternator, I would have already slapped another unit on it, but I need the 200a unit and it is a $400 unit now days. No way to prove it is failing on a bench tester and perhaps the PCM is the culprit anyway. The alternator is PCM controlled same as a factory 0411/P59 truck or van. I added a couple of wires when I swapped to the 0411 to control the alternator. Doubled my battery life on my 97.

[Fast4.7]

I made this clip a couple of evenings ago. You can see the dash voltmeter dip right at 5K rpm. Then jump right back up after the 1-2 shift.

https://youtu.be/Dyvl6LlkMcA?si=RGtFXcKZi6_o65j-

[edcmat-l1]

I've tuned thousands of GEN3s and have never experienced this. I know at some point I would have noticed it.

I'd think you'd be able to log the alt pids but if not you could hook up a scope or even a good voltmeter and monitor it that way.

What OS are you running? Wonder if a clean slate write entire would fix it. I've fixed a wide range of problems on these things with a fresh rewrite.

[blindsquirrel]

The stock gauges can do some very weird, very non-reality-based things. Do not trust them to be anything other than a mechanical idiot light.

[edcmat-l1]

The stock gauges can do some very weird, very non-reality-based things. Do not trust them to be anything other than a mechanical idiot light.

He did say in his first post he saw it first in his headlights.

[kingtal0n]

Why not throw a 470ohm resistor on the L excite and eliminate the pcm from the equation for diagnostic


I always shut alternator off or regulate down near battery voltage 12.65v~13.2 at wide open throttle for performance vehicles


This way customer is forced to use necessary fuel system and ignition components and can never complain about alternator failure destroying their engine

[SiriusC1024]

I was reading up on it last night. Some spoke about worn brushes chattering. Can't you temporarily rewire the alternator to force 100% duty cycle as a test?

The way the camera leans back from acceleration in a VAN is hilarious.

[horsepowerguru427]

Why not throw a 470ohm resistor on the L excite and eliminate the pcm from the equation for diagnostic


I always shut alternator off or regulate down near battery voltage 12.65v~13.2 at wide open throttle for performance vehicles


This way customer is forced to use necessary fuel system and ignition components and can never complain about alternator failure destroying their engine

Whats the reasoning behind reducing WOT voltage in a performance car vs a daily driver?? just the fact that itll be at WOT much more, in theory?

[kingtal0n]

Whats the reasoning behind reducing WOT voltage in a performance car vs a daily driver?? just the fact that itll be at WOT much more, in theory?

Most cars I tune are daily drivers and turbocharged performers. Daily drivers are about reliability, you give up the edge for longevity.

The fuel system needs to be able handle wide open throttle fueling without any help from the alternator, with headroom to spare for mileage and wear.
Furthermore as rpm rises and engines/alternators heating up, typically system voltage will change- usually it will drop, becomes a moving target for sensors and devices- As voltage changes a slew of variations occur for example coil dwell, injector dead-time, transmission solenoid rates, boost control solenoid frequency response, etc... it may even influence sensor accuracy. Because it is a moving target the transient delay between voltage changes and sensors behaviors cannot be adequately compensated for by any ECU.

We can easily prevent voltage variation from affecting our wot tunes and from having an impact on the fuel system output and delivery of fuel and safety by adjusting the wot system voltage near the battery voltage. The battery acts like a large capacitor and smoothing the voltage signal during wide open throttle which makes all of the sensors more accurate, the delivery of fuel more concise, the injector and coil behaviors consistent.

[Fast4.7]

The stock gauges can do some very weird, very non-reality-based things. Do not trust them to be anything other than a mechanical idiot light.

Its definitely dropping voltage. Head lights and cluster lights dim and I was able to log battery voltage. The logged voltage is 100% accurate with the dash gauge somehow. My Fluke DVM also shows the same voltage at idle at the underhood fusebox connection to the battery. I am about certain it is the PCM cutting the load at WOT. I briefly brought it up to 5,500 rpm in Park and it keeps right on charging. Even momentarily blipping the throttle WOT to fuel kill it keeps charging. Seems it has to be in Drive under full load and WOT for it to happen. I guess if the alternator goes it goes. I might bypass the regulator function as a diagnostic test but it is a real pain to get at the harness with everything assembled.

[SiriusC1024]

Most cars I tune are daily drivers and turbocharged performers. Daily drivers are about reliability, you give up the edge for longevity.

The fuel system needs to be able handle wide open throttle fueling without any help from the alternator, with headroom to spare for mileage and wear.
Furthermore as rpm rises and engines/alternators heating up, typically system voltage will change- usually it will drop, becomes a moving target for sensors and devices- As voltage changes a slew of variations occur for example coil dwell, injector dead-time, transmission solenoid rates, boost control solenoid frequency response, etc... it may even influence sensor accuracy. Because it is a moving target the transient delay between voltage changes and sensors behaviors cannot be adequately compensated for by any ECU.

We can easily prevent voltage variation from affecting our wot tunes and from having an impact on the fuel system output and delivery of fuel and safety by adjusting the wot system voltage near the battery voltage. The battery acts like a large capacitor and smoothing the voltage signal during wide open throttle which makes all of the sensors more accurate, the delivery of fuel more concise, the injector and coil behaviors consistent.

That purple font you keep using makes me think I'm stroking out lol.

Really good advice. I always enjoy your nuances and insights.

[horsepowerguru427]

That purple font you keep using makes me think I'm stroking out lol.

Really good advice. I always enjoy your nuances and insights.

Agreed.

[kingtal0n]

Every now and then you'd hear 'my alternator died and it blew my engine' sometimes on a forum.

I was like what do you mean, your alternator blew the engine? Why do people say these things, its crazy talk.

They blame the alternator when it fails, which of course it inevitably will, for causing a drop in fuel supply. Whose fault is that


Tuning an engine to be alternator dependent is like tuning methanol dependency- eventually, the pump/alt will fail and you've pretty much guaranteed your own demise.

As tuners its our job to consider cause/effect relationship and diminish or remove the potential disasters before they happen. Alt failure is a guarantee but it doesn't have to equal engine failure, that is up to us.

In other words, it should become common sense to consider all the ways an engine could be exposed to failure conditions and tune for that situation. This is one example.

Over a Decade ago, I started pulling the alternator excite wires out and tuning the engine at baseline battery voltage to find injector duty and pump output at low voltage. The first car I did to was a 1995 Toyota Supra running a power FC computer which has no alternator control feature. I wanted to make sure the fuel system could keep up because I noticed the voltage dropping at wot and figured it would be smart to test the lowest possible voltage for the 28psi on C16 making some 800rwhp on a stock piston 3L engine turning 8000rpm.


Originally just to be confident with alternator failure- but I noticed something else. The engine ran smoother. The lines on my logs were smoother. It makes a difference in the way the engine runs.

Then it just hit me. I started thinking about all the other devices which vary with voltage- injectors and pumps and sensors, whatever. They all depend on DC voltage whether its a PWM or a straight DC and they all utilize a ground feature from which that voltage signal is raised and interpreted or utilized either by a motor or solenoid or sensor. The alternator itself produces an alternating current which is rectified into a DC but there are limitations to the design of such electronics depending on the vehicle and year and components IC etc... it is not a given that the signal will be clear and clean, especially at high RPM, sometimes there is clipping or 'wings' on the edges of such a voltage signal which inherently add to the waviness of voltage output which cannot be easily detected by a digital meter or inadequate sampling.


It makes sense to keep the voltage at a steady, level, even amount, take the emphasis away from the alternators instantaneous voltage supply and rely instead on the rock with no rectifier: the battery.
I noticed the surface charge of typical batteries can maintain near 13.2v and I started using this technique target 12.6 to 13.3v depending on the vehicle for wide open throttle and have seen only benefits. Reducing alternator load frequently frees up 1 or 2hp anyways the alternator cut off switch is not a new thing. Some auto manufacturers do it anyways from the factory OEM also. It was just surprising that more people don't think about the fuel pump supply and alternator a potentially deadly mouse trap, and blindly blame obvious trap when it snaps shut as if it was unavoidable. It is absolutely avoidable.