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2006 chevy trailblazer_ls
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Discussion Starter · #1 ·
Okay I know this has been discussed at Great length with no resolution other than live with it. What I have gleaned is the ECU senses a load greater than what the alternator can generate at idle (maybe?). Not sure how my theory plans plays out yet, but I'm pursuing this. I've got an idea, just take control of the alternator away from the PCM. Put an internal regulator in the alternator, then tune out the alternator in the PCM, I do have HP tuners. Any thoughts? another thought I had was to interrupt the alternator turn on wire, which is C1 wire 2 at the PCM, or B wire at the alternator. Need to find out if it's positive on or no voltage on. I'll let you know what happens. I just don't believe there's not a fix, we didn't have problems like this before they let the ECU control the alternator, that's my theory that I'm starting with.
 

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Discussion Starter · #3 ·
Lol. Thats an open ended answer. Nope as in no ideas, or nope you dont agree?
 

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interrupt the alternator turn on wire, which is C1 wire 2 at the PCM, or B wire at the alternator.
Might want to have another look at your wiring diagrams. On my diagrams for a 2006 LL8 C1, pin 2 is not used. On the V8s C1, pin 2 is serial data.

57373
 

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Discussion Starter · #6 ·
We have a bit of a discrepancy,. Lol. And I did get it wrong I'd guess. C3-2. At any rate does anyone have any feed back? Or am I the guinea pig? Lol
 

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We have a bit of a discrepancy,. Lol. And I did get it wrong I'd guess. C3-2. At any rate does anyone have any feed back? Or am I the guinea pig? Lol

Well I posted a diagram for a 2006 based on the listing in your profile. That would be a P12 PCM.

The diagram you posted is what I have for a 2002. That would be a P10 PCM.

Have you monitored the GEN-L and GEN-F parameters to confirm your suspicions?
 

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Discussion Starter · #8 ·
Ok Google isnt very accurate in its searches, so i do appreciate the correction. No i havent had the issue long enough to monitor any parameters, although i did download a tune file from HP tuners. Doesn't look promising the Trailblazer doesn't have many parameters cracked yet. The only issue plaguing me is if i go to a one wire regulator, will the PCM catch me? Throw a CEL light and code?
 

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We tried this one wire alt on a Cadillac with a screwed-up PWM Field Circuit Driver and the alternator really wasn't happy - neither was the computer. That was "back in the day" and we had an angry customer and he just traded the car in and got a Lincoln TC.

I'll try to make this simple - as that's the way I understand it too ....... but it might take a lot of words - even for me .........

The hack you're consideration will mean that the 800Hz idle excitement won't be there any more if you go 1-wire.

So - what's this 800Hz thing about?

When the battery voltage gets low enough, the computer switches ON a "Super Excitement" 800Hz to the Field and the alternator makes more Voltage and Amperage. It has something to do with "cascadic flooring" and I'm not too sure I understand the physics of it - but I know what it does - I think.....

If one hasn't ruined his hearing with loud noises - and whilst one's head is under the hood with the engine idling --- one can hear when the 800 Hz system kicks ON and OFF.

At idle ---> when the battery Voltage starts to exceed the output of the alternator and power in the charging circuit all but halts travelling in the right direction and then the battery Voltage keeps dropping --- the PWM-Field Duty Cycle is ramped-up --- by kicking in an 800Hz digital signal to boost alternator output.

The alternator gets fed an 800Hz digital signal from the ECM that falsely saturates the Field and that makes the alternator shove out more Amperage (this is a critical part) and that Amperage is monitored by the induction/pickup coil on the negative cable from the battery (although that particular device SEEMS to be missing in the latest drawing posted).

If the "I don't see it in the drawing" Amperage Induction Sensor is missing or damaged or a wire broken - then this system falls on it's a$$.

Lest we forget about the other critical factor: VOLTAGE --- it too, if the system's healthy and working properly, will then climb, satisfying the Voltage Regulator (hence the device's name: "Regulator") and it will start lowering the alternator output by lowering the Field excitement Voltage [SEE: NOTE] - and at "TIP OFF" (of the throttle) the 800 Hz system immediately ceases to operate.

NOTE - the transition from the 800 Hz idle condition to the normal running-charging condition USED to be accomplished with going from a PWM/Digital Field Excitement Signal ---> to an analog Field Excitement Voltage.
I'm pretty sure the engineers did away with switching from Digital to Analog, a long time ago and by now ... but of this, I am not knowledgeable.

As the voltage approaches the mysterious algorithmic value that sets the ultimate charging Voltage - coupled with the Amperage that is being read - and factors in the size and temperature of the battery (I don't know how it does that - but it does) - the system is SUPPOSED to be able to pretty much handle anything the vehicle can throw at it and this is at a variety of climatic and RPM and load and temperature and speed considerations.

Put a current-sucking accessory on the vehicle's electrical backbone - and you can have troubles in all sorts of ways.

Hope this helps - but now I'm confused - however it's late and I'm going to bed as soon as I hit "Post reply"
 

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Discussion Starter · #10 ·
Well!! That was enlightening believe it or not I understand most of it enough to get a grip on what you're saying. So what you're saying is the one wire voltage regulator is not a fix. Possibly a bigger battery would solve the issue? And I got to thinking about all this mess I wonder if it isn't that the idle is set too low? According to HB tuners, I got in and looked, idle speed is set at 613 RPM from 132° up to max temp. Begs the question are v8s back when if they idle less than 800 RPM the alternator could not charge at all or very poorly. Wondering if I raise that RPM a hundred if it wouldn't solve this issue? I get that an inline 6 can idle slower, but did they get the pulley ratios set correctly to have the alternator spin at the correct speed to generate sufficiently at the desired idle speed? I know I'm getting off into this pretty deep, but I am an electronics tech and I understand the electronic side of this plus playing with cars all my life, kinda drives my brain crazy with theories
 

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I get that an inline 6 can idle slower, but did they get the pulley ratios set correctly to have the alternator spin at the correct speed to generate sufficiently at the desired idle speed?
Remember that at idle, the ECM takes over and injects that 800Hz signal into the alternator field and the rapid build-n-collapse of that high cycle rate (certainly higher than if the alternator was running at idle speed) artificially forces the output to climb - and then the voltage regulation is controlled from the inside of the ECM also - so it's pretty easy to keep a constant flow of enough current to keep things running at proper voltages.

Anything less has to be found as to the cause of the problem.

1. Bad regulator (¿ecm?)
2. Bad diode trio (it's inside the alternator - I think so anyway - or it USED to be)
3. Bad diodes on the 3-phase output (A, B, C,) - usually blown OPEN instead of shorted
4. ECM getting bad info from the Amps-sensor on the Batt-to-Engine/frame negative cable
5. ECM cannot handle alternating current (~) which should be less than 0.015AC on the DC B+ stud from the alternator
6. Bad alternator bearings - yup - they can induce a bounce to the output too!

Diode Chart
57376


Too much AC ripple in the DC Output
57377
 

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Discussion Starter · #12 ·
Ok I've read this several times, if I'm reading it correctly, this negative cable monitor is flaky? That could be our problem?? I'm not believing this is a live with it kind of deal. Has anyone tried a a new, not reconditioned, PCM? It doesn't make sense to me that these problems show up and we got to live with it, there's got to be a fix. I don't think it's throttle cracker what few times I've been able to get it title at 800 RPM it's still fluctuates on the alternator, another problem I'm having, if I rev it up and let off it'll almost die when it idles down and then it recovers. I have also had it die three times now when I let it idle and just sit with air conditioner on. Maybe unrelated maybe related just like I said earlier beginning stages of trying to figure this out
 

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OK --- think of this --- if the alternator is sending flaky (read: some AC or dropouts in the DC 12V output) to the various electronics - you COULD be getting these sorts of problems.

It has happened on many less intensively electronic'd vehicles.

I'd start with the alternator and run a diagnostic on it yourself - no way I'd trust the testers at parts houses. They often are ignorant to ripple values that are harmful to some systems and yet others can tolerate it OK.

Do your own due diligence.
 

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In part of the research you should be doing, I've pulled an interesting post from another page on this site --- it should be an eye-opener about the complexities of the charging system.

The PCM is also fed by multiple fuses, so it might be functional, but the circuit that monitors battery voltage or the alternator duty cycle might be offline.​
Check under hood fuses #10, 22, 23, 28 and rear fuse block #47​
What does the dashboard gauge read when the engine's running? If it's around 14V, then the gauge and the measuring circuit in the PCM is OK, and your problem is just in the duty cycle monitoring wire from the alternator to the PCM.​
There's a 2-wire connector at the alternator you should inspect.​
One wire is an inhibit line from the PCM to the alternator, to hold off the alternator starting up just after engine start, to prevent the additional mechanical load of the alternator recharging the battery from being added to the engine while its trying to get its idle stabilized.​
The other one is from the alternator to the PCM, and allows the PCM to see the duty cycle of the alternator, so it can judge how hard the alternator is working.​
If it sees the alternator working at 100%, but detects the voltage is dropping anyway, it goes into a "load shed" mode to try to preserve engine and transmission operation at the expense of AC, HVAC blower, lights, and so forth, to let you limp home or to safety if the alternator dies.​
 

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At this point, you've had a lot of an "Alternator 1-A Class" and you should be able to block this out yourself.

Let me know when you have some realistic test results.
 

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Discussion Starter · #16 ·
Hummmm now your making sense, ill get the oscilloscope out and have a look at waveforms, maybe look at the fields line too Also going to chech the plug tomorrow when I do the oil change. And fusses!
 

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Discussion Starter · #17 ·
Ok i checked the plug all is good there nice and new looking, there is 0.37 vAC on the line. No problems there. So I have been trouble shooting today and I am close to solving this
 

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Discussion Starter · #20 ·
Ok?? I've never seen an alternator that clean?? Not even when i was into competition stereos. But if you say so?? But that is not the whole problem. I guess I could see your point, but I'd have to have more proof. Tonight when I go home I will prove my theory and I will let you know what it is at that time.
 
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