P59 Controlling Alternator Voltage

Hi All;

I've been trying to help out with the setup of an LS swap for the last six months. I'm not a mechanic and know little about engines but been poking at computers since the early 80's, so that makes me very dangerous, LOL. Big shout out to all you guys as this site has already been very helpful in this journey.

Here's what we have to work with.
- 2007 5.3ls from a 1500 series truck (GMT800 platform)
- P59 PCM from same truck (Blue and Green connectors)
- Alternator, original to the engine when we got it has the two wire connector (L and F terminals only)

The truck originally had the separate BCM that had the current probe on the negative battery lead. We did not use that piece in our swapped setup.

We have ran the L and F alternator connections back to the PCM to terminals 15 and 75 of the green connector and also enabled the L terminal in HP Tuners under System/Options, but we can't seem to get the alternator to charge at anything other than about 13.5 volts. All the online searching we have done says that we should be able to get this setup to work and the PCM should control the voltage output of the alternator but so far we have not been able to get anything other than 13.5 volts. We have tested the alternator with a 5V PWM source and we can control the voltage so we have to assume that our alternator is working. Our backup plan is to use one of those PWM setters that people are using which at the end of the day might be a handy option to have since it can be manually set.

We believe that the P59 was used in vehicles without the BCM and it did control the alternator in the way we were expecting. We have noticed from looking at the various wiring diagrams online that in at least some of those setups the alternator used was the older 4 terminal version. (S, F, L, P connections) Is this what we are missing. Do we need to change the alternator ( OR AT LEAST THE REGULATOR) or should the P59 be able to directly control one of these two pin (F and L only) alternators?

Thanks
Jim

Need to see the tune file.

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Originally Posted by MechanicHelper

Hi All;

I've been trying to help out with the setup of an LS swap for the last six months. I'm not a mechanic and know little about engines but been poking at computers since the early 80's, so that makes me very dangerous, LOL. Big shout out to all you guys as this site has already been very helpful in this journey.

Here's what we have to work with.
- 2007 5.3ls from a 1500 series truck (GMT800 platform)
- P59 PCM from same truck (Blue and Green connectors)
- Alternator, original to the engine when we got it has the two wire connector (L and F terminals only)

The truck originally had the separate BCM that had the current probe on the negative battery lead. We did not use that piece in our swapped setup.

We have ran the L and F alternator connections back to the PCM to terminals 15 and 75 of the green connector and also enabled the L terminal in HP Tuners under System/Options, but we can't seem to get the alternator to charge at anything other than about 13.5 volts. All the online searching we have done says that we should be able to get this setup to work and the PCM should control the voltage output of the alternator but so far we have not been able to get anything other than 13.5 volts. We have tested the alternator with a 5V PWM source and we can control the voltage so we have to assume that our alternator is working. Our backup plan is to use one of those PWM setters that people are using which at the end of the day might be a handy option to have since it can be manually set.

We believe that the P59 was used in vehicles without the BCM and it did control the alternator in the way we were expecting. We have noticed from looking at the various wiring diagrams online that in at least some of those setups the alternator used was the older 4 terminal version. (S, F, L, P connections) Is this what we are missing. Do we need to change the alternator ( OR AT LEAST THE REGULATOR) or should the P59 be able to directly control one of these two pin (F and L only) alternators?

Thanks
Jim

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I do a lot of swaps. We typically do not let the ECM/PCM control the alternator. A 470 ohm resistor on the "brown" wire going to the alternator will get it going.

Google "LS swap 470 ohm resistor" and you'll find plenty about this.

Blindsquirrel;
Thanks for the info. So you figure we need to change the alternator to a 4 wire type in order to get the P59 to control it?
Jim

Alvin;
We went down that road and from all the info we managed to find on the 470 ohm resistor fix we thought that it only works on the four wire alternators. We currently have the two wire. Will it work on both alternator types?
Jim

Yes.. Some GEN 3's are only 1 wire and it works just fine.

Maybe need something like this?
https://speedmaxinnovation.com/produ...control-module

Is it bigger than a breadbox? (this is how it works if there's no tune file to look at, we get to play 20 Questions instead)

What's in your tune file at System Options for F/L terminals? Would go much smoother if there's something to look at.

2 wire & 4 wire alts are the same, they just have different plugs. They both only use only the F & L terminals and you can swap from one to the other and don't have to change anything but the connector. I guess GM finally accepted that they were never going to have an application that used the S & P pins, and got rid of them.

Quote:

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Originally Posted by gtstorey

Maybe need something like this?
https://speedmaxinnovation.com/produ...control-module

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Yes, that's a gadget that would work.
Thanks
Jim

Quote:

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Originally Posted by blindsquirrel

2 wire & 4 wire alts are the same, they just have different plugs. They both only use only the F & L terminals and you can swap from one to the other and don't have to change anything but the connector. I guess GM finally accepted that they were never going to have an application that used the S & P pins, and got rid of them.

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They are not just different plugs. The regulators work completely different. The 4 pin uses a current limited 12 volt signal on the L terminal and the 2 pin uses a 5 volt PWM signal on the L terminal. If I had quick access to the tune file I would post it for you. We have both the L and F alt functions enabled in the System/Options menu of HP Tuners.

Jim

Hi all
I have a 2004 LQ9 swapped into my Malibu when I look under System the Alt F option is set a 1 and the Alt L option is set at 0.
In your original post you mentioned that you turned on the Alt L option, could this be part of the problem?
I'm no expert and may have missed something, so I'm just throwing out ideas.

Quote:

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Originally Posted by LongRoof81

Hi all
I have a 2004 LQ9 swapped into my Malibu when I look under System the Alt F option is set a 1 and the Alt L option is set at 0.
In your original post you mentioned that you turned on the Alt L option, could this be part of the problem?
I'm no expert and may have missed something, so I'm just throwing out ideas.

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No one is an expert, LOL. Thats why we are on these forums. Thats interesting, I believe the 2004 LQ9 used the 4 pin regulator with the L and F terminals wired back to the PCM (no separate BCM). I would have figured your L terminal would be enabled in the PCM. Our P59 PCM also had it disabled in stock form. We have tried it both ways and neither has worked for us. Our setup is a 2007 5.3 that used the 2 pin regulator and the external BCM. So having the L terminal disabled in the PCM makes sense to me since the BCM was doing this for us.

Thanks for the info.
Jim

I don't know if this guy knows what he's talking about, but goes into pretty good detail.
https://speedmaxinnovation.com/blogs...you-could-need

Quote:

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Originally Posted by gtstorey

I don't know if this guy knows what he is talking about, but goes into pretty good detail.
https://speedmaxinnovation.com/blogs...you-could-need

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Ya he goes into great detail. From what he is saying the 2 pin and 4 pin regulators are very different beasts. I think we have enough background on this issue to decide where to go next. Thanks all for your help.
We will try one of the manual adjustment setups for the 2 pin version. Here is one such device we can purchase, but there are a bunch of different option out there.

https://brand-x-electrical.myshopify...05-gm-vehicles

Jim