F body Altenator on LS1

Now I'm having alternator problems, using a new F body alternator excited by the PCM Red pin 15.
Has blown three voltage regulators. Each time it went back to the alternator shop for pro work.
Voltage on trigger wire is 10.4. Battery is in good shape.

Has anybody had problems with triggering F body alternators? I'm seriously thinking of changing to one wire and by passing the PCM

Take a look at this thread and see if it helps, I have a single wire alternator with a 470 Ohm resistor inline and my alternator works fine, my harness came with the resistor.

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I can't say anything about trigger issues but I can speak about the F body alt in general. My wife's 2002 Camaro SS factory installed alternator started acting funny last week (170,000 miles has that effect on things .)
After a bit of looking on the LS boards it appears that no after-market alternator manufacturer/re-manufacturer can build one that will last, but the factory installed Delco or Bosch units work wonders until they die. It appears that whatever regulator is being used by these re-manufacturers never has what it takes. Even the alt/starter shops don't seem to produce the goods.
Most people are picking up the 145 amp truck alternator (stock Camaro is 102 amp), option "KG3" from trucks of 2005 vintage. I got a used, factory installed unit, last week for $65 shipped. Installed in an hour and bam! 15 volts on a cold start, and it has not dipped below 14 yet. Got it from car-parts 2005 Chevy truck 2500 series should get you what you need.
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Here is the post that I found most informative on the KG3 alternator (and other choices if you have time to read it all). The KG3 is a direct fit but you will not be able to use the rear mount.
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This is the reason why I mounted the 5.3/6.0 truck alternator from the start. Performancetrucks has similar threads. I think SSP sent a 1-wire plug, I'll have to double check. If there is no resistor there, should I solder one in?

The GTO alternator is a higher output unit, also. If you have the check light for the alternator working on the dash you won't need a resistor. The late models have a light and a backup resistor in case the light burns out. The alternator wiring from the Porsche is wired through the alarm, if you removed your alarm and did the bypass correctly there should be no problem there. I put a resistor in line with my alternator and the light on the dash would not come on. When the resistor was removed the light came on and everything worked as it should, so far.
I had a rebuilt alternator from Advance bench tested, it didn't work right out of the box.

Just been to the alternator shop and confirmed that the regulator is fried for the third time.

I'm using the standard LS1 alternator set up and only place it interfaces with the Porsche is the main output cable from the alternator to the battery.

The PCM has a trigger wire from Red Pin 15 that goes to the alternator and turns on the alt when the engine is running, voltage on this wire is 10.5 volts. My alt shop thinks that this wire may being grounded as that could destroy the regulator. This setup is called two wire and does not require a resistor in the trigger line.

I have ordered a self exciting one wire regulator which will completely divorce the alt from the PCM.
Going to beat this until something else quits.

Arthropraxis......not sure what alternator wire in the Porsche you mention. My alt has been separate from the Porsche except for the PCM trigger.

This sounds just like my problems with the quest alternator on my turbo motor. Bought a rebuilt unit, regulator died within 2 months. Had the reg. replaced at local shop, then the new reg. dies in less than a month. I wonder if there is just a huge batch of crap regulators out there right now? Seems like several people here have had their gm alternators go out as well. I have a hard time believing the wiring is the problem.

Can someone tell me what the voltage level of the alternator turn on signal at Red pin 15 should be.
I have read elsewhere that if this voltage is high it can destroy the alternator regulator.
The GM wiring schematic shows a direct wire from this pin to the alternator. I believe that earlier PCM's required a resistor.

Schematic here:

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The alternator wire I was referring to comes off of the two pin connector at the firewall. One Red/bl wire goes to the starter the other, a blue wire goes to the alternator. The GTO alternator does not connect to the PCM. It is a two wire hookup. One wire to the blue Porsche alternator/voltage gauge, the other wire directly to the battery.

Thanks Arthropraxis,
You can go two ways with the alternator hook up, the method you used or the stock LS1 method.
My modified harness came back from SSP Wiring with a single wire connector to fit the Camaro alternator. (This is called a two wre alternator, power out and trigger)

This is the wire from Red Pin 15 on the PCM that you can see in the referenced schematic.
As I have destroyed three regulators I am thinking that the voltage on this pin is out of specification.

I have overcome the problem by converting the alternator to one wire self exciting.
My voltmeter works fine as it monitors the system voltage somewhere in the car.

Having blown three regulators in a F body Alternator, my rebuilder suggested converting it to one wire (only the wire to the battery) making it self exciting.
This was done and refitted, finally have a reliable alternator that is totally divorced from the PCM.

I have reduced the PCM/Porsche connections to the following:

+12 volts battery
+12 volts switched ignition
Fuel pump
Tach
VSS input.
Added later.....Fan triggers

For single wire PCM driven alternators you need 12v resisted by 470ohm 1/2 watt resistor inline (8.2v after resistor) to pin B and ignition switched 12v to pin C. This means buying a four wire pigtail and removing wires for A and D.

The single wire coming from the PCM (which actually receives the on/off signal from the body control module) is pin B.

I went to a truck alternator as well for the higher amperage, but this wiring works on all of these alternators up to 2002 as far as I know.

Marc,
Thanks for your input, if you check the Electrical schematic for the F body cars you can see how the alternator (Generator) is wired, the main output wire is connected to the starter motor and on to the battery, the other wire (turn on signal) to B is from the PCM pin 15 C2. This is how I wired my car and it was destroying regulators. I can only assume that my PCM is faulty in some way. I see no requirement for a resistor. I would appreciate any information for a data source that indicates the need for a resistor.

I changed my setup from a two wire to a single wire (self exciting) regulator which is independant of the PCM and any other vehicle wiring and the same alternator is now behaving fine.

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Mike,

The diagram that you have does not show the relationship between the body control module and the other side of the PCM. The PCM, when told by the BCM, generates 5volts to the single wire going to the alt pigtail. We do not keep the BCM so the wire from the PCM does nothing, therefore no charging. If you put 12v to the C terminal the alt will not function.

I did a lot of reading on lstech and this is the fix that worked for me. So I run one wire powered by the ignition and split it with the resistor going on B and 12v going to C.

That's good news, Mike. Nice small list. So are you running the factory Porsche thermo switch to control the fans then? I keep reading about rewiring it to the Chevy PCM and adding relays and I wonder why when the 944's control stuff all seems to be intact.

I think I've found the late 944 setup turns both fans on low speed at 92C and high speed at 102C. This is considerably lower than Painless reports the Chevy 411 PCM fan outputs as Fan1 turns on at 226F and Fan2 at 235F. Seems to be the same ballpark. Any issues in just leaving the 944 controls?

Rich

Rich,
Sorry I left of from my list that the PCM fan triggers (switched grounds) are used to control two relays that control each fan. I'm not using the three relay method but thinking about it because the stock Porsche fans are so noisy at full speed. The fan relays follow the PCM programmed on/off temps.

I have also placed additional relay contacts in series with the fan feeds, so when the compressor turns on it turns on both fans. After having trouble with the PCM wiring I didn't want additional problems.
When I get the AC system leak proof and charged I will try using the PCM AC request wire to see if it will increase the idle with the air on.

Here are my PCM Fan temps.

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Cool, thanks Mike. That might be the best way to do it. I was just reading in some of the old threads and I see that Admin has a strong opinion to do it the PCM way. Doing so would give me that port on the radiator for my temp gauge too.

Rich

Never thought about that. What is the thread size for the port on the radiator?

Hey Arthropraxis. Looks like it's 22mmx1.5 but I'm not finding an adapter to 1/8" NPT for this thermocouple. So, did the deal you described work of pulling out the wires to the temp switch and connecting them to the PCM? The PCM outputs for Fan1 and Fan2 switch to ground, as Mike describes. This drives your fans on hign and low properly?

Rich

Yes, it seems to run fine. The system will run as the original Porsche system. Both fans will run at high or low speed as needed. The relay will get the signal from the PCM, the PCM gets it's signal from the GM temp sender in the drivers side head.

Don't forget to use relays between the fans and the PCM fan triggers, this is the three relay version that runs two fans in series at low speed. Diagram here:

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Sorry to jack your alternator thread, Mike. Good diagram of the 3 relay method. Arthropraxis did it differently described by him toward the bottom of page 2 of this thread:

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So I have 3 options: A) old switch and relays already in the car, B) new relays driven by the Chevy switch in the PCM, C) old relays driven by the switch in the PCM. The last one is the "hybrid" approach...

Rich

P.S. Sent from Waikiki beach!

Rich,
Enjoy the beach, I used to fly LAX-HNL-LAX and we laid over in Waikiki. Good food.
Loved the street performers at night and the Coldstone Creamery. There used to be a place where you could rent Ferraris and Porsches by the day.
Enjoy