Explanation of E38 ECM and Alternator Voltage Control/ECM Override Settings Requested

[scottt28]

I have an GEN IV E38 ECM running my 408 LS. The wiring harness was made by Speartech. I am using a complete Holley LS Engine Swap Accessory Drive Systems Part #20-138 that includes a 130 amp alternator. The engine is swapped into a 2001 Chevrolet S10. I removed the stock S10 ECM that ran the original V6. The truck died over the weekend. In the scan file (NOT attached because it is huge), I can see the voltage to the ECM drop from 13 something down to about 6 volts. Before it died, the GM 4L85E Supermatic transmission was not shifting correctly , the radio came on and off, and the truck was acting weird.

I had the truck jumped started, but it was clear the battery either 1). wasn't being charged by the alternator, or 2). the battery was totally junk and would not accept a charge, or 3). wiring to/from the battery/alternator was loose etc, or 4). some combination of #1 and #2 and #3.

Wiring at battery, master disconnect switch, starter and alternator etc looks fine. With a new battery installed, I am only getting 11.something volts. After some research, I found that the ECM might control the alternator on this setup. Here are the two settings that I see in HP Tuners:

SYSTEM > GENERAL > ALTERNATOR > VOLTAGE CONTROL
SYSTEM > GENERAL > ALTERNATOR > ECM OVERRIDE

My tune shows "Not Fitted" and "Disabled" for Voltage Control and ECM Override respectively. Tune file and screen shot attached.

Would simply changing the VOLTAGE CONTROL and ECM OVERRIDE to "Fitted" and "Enabled" fix my problem? I am expecting to see 13.6 volts to 14.5 volts during normal operation.

I'm reading up on the subject, but I'm not understanding the whole deal yet. If someone wants to chime in with a educated response, I would appreciate it.

[99socalfrc]

Does the harness actually connect to the 4 pin connector on the alternator? Most swaps simply take the correct wires off the 4 pin connector to a switched 12v. This then excites the alernator totally independent of the ECM.

[scottt28]

This is the SpearTech harness. On the top of the alternator, there is a connector with three wires. The orange wire at the top has the same voltage as the lug with the 10mm nut shown on the back of the alternator.

[scottt28]

This is the SpearTech harness. On the top of the alternator, there is a connector with three wires. The orange wire at the top has the same voltage as the lug with the 10mm nut shown on the back of the alternator.

Still researching. Anybody experience this issue?

[Montecarlodrag]

You will not be able to control the charge voltage in a new alternator (2 pin) without a BCM or a BCCM.
They use a different type of regulator which needs a PWM signal to control the charge. The ECM can't output this signal, this work is done by the BCM or BCCM. It doesn't matter the setting you change in the tune, it will just not work. If you feed 12V to it or hook a resistor bulb won't work either.
If this pwm signal isn't present the regulator will default to 13.8 V and stay there always, which is good for 99% of the cars out there.
If you want true charge control install and wire a BCM or change the alternator regulator to an old one (4 pin), or buy another alternator.

[scottt28]

You will not be able to control the charge voltage in a new alternator (2 pin) without a BCM or a BCCM.
They use a different type of regulator which needs a PWM signal to control the charge. The ECM can't output this signal, this work is done by the BCM or BCCM. It doesn't matter the setting you change in the tune, it will just not work. If you feed 12V to it or hook a resistor bulb won't work either.
If this pwm signal isn't present the regulator will default to 13.8 V and stay there always, which is good for 99% of the cars out there.
If you want true charge control install and wire a BCM or change the alternator regulator to an old one (4 pin), or buy another alternator.

Not sure I understand your response. The engine is being controlled by an E38 PCM. The stock PCM from the S10 is gone, but the stock BCM is right above the trans hump under the dash. And to be honest, I never knew what a BCM was until recently. Anyway, does the new E38 PCM somehow work with the stock 2001 S10 BCM to control the voltage output from the alternator? If so, how does it get wired up? I haven't got a clue.

And while we're on the subject, does anybody know how I can get my stock 2001 S10 gauges to work with an E38 PCM, stock BCM?

[scottt28]

Also... the picture of the alternator shows what appears to be 4 pins. It is a 130 amp alternator supplied in the Holley LS Engine Swap Accessory Drive Systems Part #20-138. It is different than the 2 pin regulator that I am used to from the old days.

[realsquash]

The E38 controls the field on the alternator directly. The ECM gets input from the BCM (via the CAN bus), which has a current sensor on it. I think that if you don't have the BCM you need to flip on the override in the tune and also voltage control needs to be enabled. I'd flip them and see what it does. Or go the hardwired route as mentioned.

[scottt28]

The E38 controls the field on the alternator directly. The ECM gets input from the BCM (via the CAN bus), which has a current sensor on it. I think that if you don't have the BCM you need to flip on the override in the tune and also voltage control needs to be enabled. I'd flip them and see what it does. Or go the hardwired route as mentioned.

Sitting in the driveway, Voltage Control = "Fitted" and ECM Override "Enabled". I am seeing 10.80 volts as "Control Module Voltage".

How exactly do I "hard-wire" this thing?

[afasts10]

i was having the issue as you are.
I just used the original alternator and used the original wiring on my s10.
everything works perfect now.

[scottt28]

i was having the issue as you are.
I just used the original alternator and used the original wiring on my s10.
everything works perfect now.

That's cool, but I sold the original engine and transmission with the original wiring/ECM to help pay for the LS setup. I have an all-new harness, ECM, alternator... I'm trying to figure out how to get it to charge correctly with the aftermarket Holley alternator/accessories setup, and a E38 ECM and a completely new SpearTech harness.

[realsquash]

I don't have the pinouts here in front of me, but that looks like a CS130 alternator, which just needs a couple of +12 connections to operate without any thing connected to the ECM.

[afasts10]

I did quite a bit of research on this and never got an answer that would work.
I hope you can get it worked out. I would like to be able to used the other alternator.

[pganci]

I also have a Speartech harness and had an issue with Voltage drop as engine temperatures went up. When first started i would be at 12V at idle and once cruising around it would drop to 10V at idle. After upgrading to a 200+ alternator and still having the problem i started digging and found this article about Remote Voltage Sensing. The alternator has a Sensor Pin that is not being used or at least not on my Speartech harness. I checked the voltage output at the alternator and it was 13+Volts but the bus bar on the fuse block was 2 - 3 volts less. I added a 10 gauge wire from the S pin to my the bus bar and now have 13 plus volts at idle.

Here is the article i copied. Hope it helps.

Remote Voltage Sensing

This is where the concept of REMOTE voltage sensing comes into play. Instead of sensing system voltage at the alternator or close to it (which is like congratulating yourself on a great job regardless of the results!) - we sense system voltage where we need full voltage - in this case at the main distribution point (bus bar).

That way, when the voltage sensing circuit detects 13.0 volts at the main bus bar, it says: " I'm supposed to produce and output sufficient to maintain system voltage at 14.0 volts. I sense system voltage as 13.0 volts. Better increase output to 15.0 volts to bring system voltage up to 14.0 volts."

Such a system would look like this (note the remote voltage sensing wire, highlighted red):

Voltage Sensing.jpg

Another advantage to this remote voltage sensing, is that it allows the alternator to compensate for increased system demand as more accessories are turned on. That's what it's supposed to do, after all. As more and more devices are switched on, a voltage drop will occur at the main bus bar. With remote voltage sensing, the alternator sees this drop caused by the extra demand, and automatically increases output to compensate. To not use remote voltage sensing, or to simply jumper the wire to the alternator output or some other nearby source would be like hiring a blind sniper - sure you might hit the target, but only by blind luck!

Now - if you're thinking about what I've just written and looking at the diagram and thinking: "But why do I need that #10 GA wire for voltage sensing? I already have that big fat #2 wire going from the alternator to the bus bar - why not just jumper that to the voltage sensing terminal?" well, all I can say is I am soooooo disappointed in you! ;-) Have you forgotten Part 1 so quickly? Remember voltage is the "electrical pressure" difference between two points and that voltage is related to current flow and resistance. In the diagram above - as system demands draw more and more current, so the voltage at the bus bar will drop. However, if we take our voltage sensing directly from the alternator output, we will only be reading alternator output not system voltage, despite the fact that the #2 wire connects to the bus bar - the current is flowing from the alternator output to the bus bar, not the other way around, and it is "losing pressure" as it goes. If we just jumper the #2 wire to the voltage sensing terminal, we are reading the "pressure" at the beginning of its journey, and yet we know it decreases as it goes. On the other hand, the advantage to the #10 voltage sensing wire is that very, very little current flows through it, and this doesn't vary with system demand (i.e. when we switch more stuff on) AND it is sensing the voltage at the END (or at least the middle) of its journey, which is what is important to us.

Also, note that connecting the remote voltage sensing terminal to the battery will only result in the alternator being a good battery charger - it still won't compensate for voltage drop in the system caused by wiring to the main distribution point and increasing electrical demand as more components are powered on.

Also note that this "main distribution point" system only works properly when the “battery charging wire” connects from the main distribution point to the battery (as seen in the diagrams above). There should never be a wire connected from the alternator directly to the battery. This is because, the voltage regulator can only "sense" and "respond to" one voltage - in this case the voltage at the main distribution point. If we also ran a heavy gauge charging wire from the alternator directly to the battery, we risk dangerously overcharging the battery as the alternator adjusts output to maintain the main distribution point at 14.0 volts. That's why the battery must also take its charge from the main distribution point - so the system is in equilibrium and we don't risk sending 16.0 volts directly to a battery because that's what the alternator is outputting to keep the main distribution point at 14.0 volts.

[scottt28]

Howdy... I talked to Justin @ SpearTech. We confirmed that the harness was built correctly and that the settings in the tune were initially correct i.e "Not Fitted" and "Disabled" for Voltage Control and ECM Override respectively.

I have a new battery. Negative side grounded to the frame (in a couple of spots) and to the transmission. Positive side of the battery runs to a master disconnect switch mounted on the rear of the frame. From the master disconnect switch, power goes to the starter. From the starter, power goes to a 175 amp fuse (ideally, the fuse should be before the starter... but it didn't happen that way). I believe pganci is using a "bus bar" as described above. I basically connected everything to the end of the fuse - the end of my fuse is the main distribution point.

Picture of the 175 amp "big fuse" attached. The alternator lug is attached to the left side of the fuse with a 4 gauge wire. (Fan relays/fuel pump relays, fuse block etc are also connected to the left side of the fuse too). The right side of the fuse receives power from the lug on the starter with another 4 gauge wire. Starter is connected to master shutoff switch, then the battery with a heavy 2/0 gauge wire.

Holley makes a single wire connector shown in the attachment. I put the connector into the alternator and applied battery voltage directly from the lug on the back of the alternator. See artwork attached. I didn't see any change in output. Then I noticed the Holley pinout might be wrong, so I moved the single wire to the "S" location (signal) on the alternator. I then applied battery voltage to the "S" ... no change in output

[GFB Performance]

I had an issue when doing a Gen 3 Hemi swap in a 70 Charger and using a Holley Dominator EFI. The Holley doesn't provide any output to control the alternator so I used these guys adjustable unit and it worked great. https://alternatorparts.com/ Hope it helps

[scottt28]

I had an issue when doing a Gen 3 Hemi swap in a 70 Charger and using a Holley Dominator EFI. The Holley doesn't provide any output to control the alternator so I used these guys adjustable unit and it worked great. https://alternatorparts.com/ Hope it helps

On Oct 7 at 6512 RPM and 101 mph, Control Module Voltage dropped from 13 something to 11 something in a fraction of a second. You can see it at 22:05 of the attached scan. In the software development world, we always ask ourselves "what changed?" when something doesn't work. Since the battery, wiring etc didn't change, I think the alternator might have died. Everything is new, but so was the starter and the drive-by-wire gas pedal. New build blues i guess... The alternator was part of the Holley accessories kit I bought from Summit, so I am waiting for them to ship me a replacement under warranty.

[scottt28]

Replacement alternator showed up and I am charging again. I'm seeing 13.2 or so Control Module Voltage. Seems low, but better than discharging.

[rpmextreme]

Replacement alternator showed up and I am charging again. I'm seeing 13.2 or so Control Module Voltage. Seems low, but better than discharging.

Your E38 needs to see a charging request signal from the BCM before it will charge more than 13.2. It's currently in default mode. We have a module that will send the correct charging signal and get you up to 14.2 or so. Send me a PM if interested.

[HartRod]

Your E38 needs to see a charging request signal from the BCM before it will charge more than 13.2. It's currently in default mode. We have a module that will send the correct charging signal and get you up to 14.2 or so. Send me a PM if interested.

Any more information on this?