Gen V Swap Alternator

[gofast321]

Hi everyone. Just finished a L83 Gen V swap in my 1988 Suburban (attached) and I love the way it turned out. However, I'm having some alternator issues and was curious how some of you fixed it in your swaps.

My alternator performance is hit or miss. Sometimes it will charge at 13.6 volts but other times it won't charge at all. I assume this is because I don't have a BCM and the alternator is just in a limp mode. I don't have a big stereo or off road lights but I do run the front and rear AC, plus dual electric cooling fans, and a fuel pump so I'm concerned that the alternator won't keep pace. Or I won't notice one of the times when its not charging and will drain the battery.

I have heard that adding the 470 ohm resistor to the brown (L) wire in the alternator wiring should fix this (similar to LS swaps) but I have also read that it doesn't work on the Gen V stuff.

Do any of you Gen V swap guys have a solution here?


Thanks,
Chad

[Nick_R_23]

You have what is called a PWM alternator, which can step its output voltage based on a signal supplied from the ECU. Unplugging it should allow it to run in a default output, but you can also pick up a small PWM controller or PWM generator and command it to whatever voltage output you prefer.

This thread should have a lot on information for you:

https://ls1tech.com/forums/conversio...hrow-away.html

Edit: If you are running a factory ECU/tune with your swap, then it is completely normal for the alternator to show a low output state. The ECU will lower the alternator output to improve fuel economy under certain conditions.

[Nick_R_23]

Here is also a description of what variables the system uses to determine how the alternator operates.


Charging System Operation
The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:

• Battery Sulfation Mode

• Charge Mode

• Fuel Economy Mode

• Headlamp Mode

• Start Up Mode

• Voltage Reduction Mode

The engine control module (ECM) controls the generator through the generator turn on signal. It monitors the generator performance though the generator field duty cycle signal circuit. The signal is a 5-volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-95 percent. Between 0-5 percent and 95-100 percent are for diagnostic purposes. The following table shows the commanded duty cycle and output voltage of the generator:


The generator provides a feedback signal of the generator voltage output through the generator field duty cycle signal circuit to the ECM. This information is sent to the body control module (BCM). The signal is a 5-volt PWM signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99 percent. Between 0-5 percent and 100 percent are for diagnostic purposes.

Battery Sulfation Mode
The BCM will enter this mode when the interpreted generator output voltage is less than 13.2 volts for 45 minutes. When this condition exists the BCM will enter Charge Mode for 2-3 minutes. The BCM will then determine which mode to enter depending on voltage requirements.

Charge Mode
The BCM will enter Charge Mode when ever one of the following conditions are met.

• The wipers are ON for more than 3 seconds.

• GMLAN (Climate Control Voltage Boost Mode Request) is true, as sensed by the HVAC control head. High speed cooling fan, rear defogger and HVAC high speed blower operation can cause the BCM to enter the Charge Mode.

• The estimated battery temperature is less than 0°C (32°F).

• Battery State of Charge is less than 80 percent.

• Vehicle Speed is greater than 145 kph (90 mph)

• Current Sensor Fault Exists

• System Voltage was determined to be below 12.56 volts

• Tow/Haul Mode is enabled

When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9-15.5 volts, depending on the battery state of charge and estimated battery temperature.

Fuel Economy Mode
The BCM will enter Fuel Economy Mode when the ambient air temperature is at least 0°C (32°F) but less than or equal to 80°C (176°F), the calculated battery current is less than 15 amps and greater than -8 amps, and the battery state of charge (SOC) is greater than or equal to 80 percent. Its targeted generator output voltage is the open circuit voltage of the battery and can be between 12.5-13.1 volts. The BCM will exit this mode and enter Charge Mode when any of the conditions described above are present.

Headlamp Mode
The BCM will enter Headlamp Mode when ever the headlamps are ON (high or low beams). Voltage will be regulated between 13.9-14.5 volts

Start Up Mode
When the engine is started the BCM sets a targeted generator output voltage of 14.3 volts for 30 seconds.

Voltage Reduction Mode
The BCM will enter Voltage Reduction Mode when the calculated battery temperature is above 0°C (32°F). The calculated battery current is less than 1 amp and greater than -7 amps, and the generator field duty cycle is less than 99 percent. Its targeted generator output voltage is 13 volts. The BCM will exit this mode once the criteria are met for Charge Mode.

Instrument Panel Cluster (IPC) Operation
Charge Indicator Operation
The instrument panel cluster (IPC) illuminates the charge indicator and displays a warning message in the driver information center (DIC) when the one or more of the following occurs:

• The engine control module (ECM) detects that the generator output is less than 11 volts or greater than 16 volts. The IPC receives a GMLAN message from the ECM requesting illumination.

• The BCM determines that the system voltage is less than 11 volts or greater than 16 volts.

• The IPC receives a GMLAN message from the body control module (BCM) indicating there is a system voltage range concern.

• The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

• The ignition is ON, with the engine OFF.

Battery Voltage Gauge Operation
The IPC displays the system voltage as received from the BCM over the GMLAN serial data circuit. If there is no communication with the BCM then the gauge will indicate minimum.

Utilities and light duty full size pickups are equipped with a new regulated voltage control (RVC) system. This system turns off the alternator when it is not required in order to improve fuel economy. The generator will turn back on when additional voltage is required. This will cause the voltmeter to fluctuate between 12 and 14 volts as opposed to non-regulated systems which usually maintain a more consistent reading of 14 volts. This fluctuation with the RVC system is normal system operation and NO repairs should be attempted.

SERVICE BATTERY CHARGING SYSTEM
The BCM and the ECM will send a GMLAN message to the DIC for the SERVICE BATTERY CHARGING SYSTEM message to be displayed. It is commanded ON when a charging system DTC is a current DTC. The message is turned OFF when the conditions for clearing the DTC have been met.

[gofast321]

Thanks for the info Nick, I appreciate it.

Quick follow up question... If I don't use a PWM controller, I understand the alternator will run in a default mode. In cases where the ECM commands the alternator to stop making voltage will it eventually command the alternator to turn back on? I haven't run the truck long enough to determine that. Times when I have noticed that the alternator is not producing voltage I have just restarted the truck and the alternator has gone back to 13.6-8 volts after restarting. If I was on a long trip and the alternator stopped making voltage would it eventually come back on without restarting the truck?


Thanks

[Nick_R_23]

From the way I understand them, completely unplugged aside from the battery cable, the alternator should default to an output voltage of 13.6-13.8v and maintain that. I do not believe that they are supposed to deviate from that default voltage.

[gofast321]

I just tested mine tonight and unplugged the 2 pin harness. It did read 13.6 volts, however, when I turned on the front and rear ac and headlights the voltage dropped to 12.4. So based on the articled you referenced Nick I ordered a PWM generator. I'm going to set it to run the alt at about 14.4 volts and I'll just hide the controller under the dash somewhere.

Also the generator I ordered was from TKXEC and the model was XY-APWM. What's nice about this one is that you can use a 12v source but set the PWM output to the 5v the alternator needs.

Anyway, thanks for the help Nick, that was definitely the info I needed.

[87chevy.com]

old thread, just adding information for others

My stock alternator settings did the same thing. Sometimes the gauge was 13 volts - ish.... others would be below 12 on the gauge... annoying.... then came across some info

HPTuners required

go to

System Tab / General

Fuel System Voltage Min

Set this to the desired Voltage output. In one of my swaps 2006 BMW x5, I have it set to 14v, and it outputs 13.6v. So tweak it as needed

Fuel System Delay : delays the alternator commanded on voltage for however long you set this delay to. I give it 10 seconds, think it was a factory value just so its not loading the engine right on startup.