Alternator always on?
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Joined: Apr 2019
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Alternator always on? Hello,
I have swapped a LQ4 from a 2002 GMC Denali into my 1989 Firebird GTA- using LS1 intake, wiring harness, and f-body LS1 accessories. Im using the the truck ECM with the truck Delphi injectors (I had to do some tuning to make the 3 wire MAF work as well as the non-vacuum referenced FPR). So anyways, everything worked great for about a week, then i went to start the car and the battery was dead. Hmmm... I had been fixing the hatch pull down motor and thought that was the problem, but the battery still went dead. I got my clamp style amp meter out and started checking wires. I found that the Alternator was drawing .53 amps with the car off and everything powered down. So, i though it was probably a bad alternator. When i pulled the L connector off the alternator, the draw stops. Plug it back in, and the draw is there. Sometimes it will draw and other times it wont. I ordered a new alternator and placed it in the engine bay and hooked it up with jumper cables. It was also drawing ..... I measured the L terminal wire and i get 4-5 volts with everything off. I pulled up the starting /charging diagram for the 2000 Silverado LQ4 tune that i am using, and found that this alternator uses two wires(GEN F and GEN L) whereas a 2000 LS1 F-body(the alternator that i am using) uses a single wire on terminal L to C2 Pin 15. The truck diagram shows C2 pin 15 as GEN L as well... Any ideas on why i still have voltage on this wire when it should be off? Is there something different between the F-Body tune and the truck tune that i am missing?
Thanks,
Derek
I have swapped a LQ4 from a 2002 GMC Denali into my 1989 Firebird GTA- using LS1 intake, wiring harness, and f-body LS1 accessories. Im using the the truck ECM with the truck Delphi injectors (I had to do some tuning to make the 3 wire MAF work as well as the non-vacuum referenced FPR). So anyways, everything worked great for about a week, then i went to start the car and the battery was dead. Hmmm... I had been fixing the hatch pull down motor and thought that was the problem, but the battery still went dead. I got my clamp style amp meter out and started checking wires. I found that the Alternator was drawing .53 amps with the car off and everything powered down. So, i though it was probably a bad alternator. When i pulled the L connector off the alternator, the draw stops. Plug it back in, and the draw is there. Sometimes it will draw and other times it wont. I ordered a new alternator and placed it in the engine bay and hooked it up with jumper cables. It was also drawing ..... I measured the L terminal wire and i get 4-5 volts with everything off. I pulled up the starting /charging diagram for the 2000 Silverado LQ4 tune that i am using, and found that this alternator uses two wires(GEN F and GEN L) whereas a 2000 LS1 F-body(the alternator that i am using) uses a single wire on terminal L to C2 Pin 15. The truck diagram shows C2 pin 15 as GEN L as well... Any ideas on why i still have voltage on this wire when it should be off? Is there something different between the F-Body tune and the truck tune that i am missing?
Thanks,
Derek
Derek,
I can't help directly, but you are on the right track. Pin L should only be getting power with the ignition in the ON position. So the L terminals is either in the wrong ECU pin or something is up with the tune.
Andrew
I can't help directly, but you are on the right track. Pin L should only be getting power with the ignition in the ON position. So the L terminals is either in the wrong ECU pin or something is up with the tune.
Andrew
Thread Starter
Teching In
Joined: Apr 2019
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Thanks Andrew.
I bought the harness off ebay. It is a stock F-body LS1 harness. Although i did notice that the alternator connector had been cut off... Maybe the previous owner encountered a problem with it? And had to do a work around... Im going to go check and see if there is a red wire in C2 #15.
I bought the harness off ebay. It is a stock F-body LS1 harness. Although i did notice that the alternator connector had been cut off... Maybe the previous owner encountered a problem with it? And had to do a work around... Im going to go check and see if there is a red wire in C2 #15.
Thread Starter
Teching In
Joined: Apr 2019
Posts: 13
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No real progress yet. The wire is going to the correct place on the ECM. I looked through Hptuners looking for things to change. I found that the F terminal is enabled and the L terminal is disabled. Platform is GMT800. Do I need to change the platform type to F?
I've run into this on two different F body engine swaps before and it was always a bad alternator. One of them you could actually here the alternator buzzing with the key off. Very strange that the alternator wasn't the fix for you. Hope you get it figured out man.
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Thread Starter
Teching In
Joined: Apr 2019
Posts: 13
Likes: 2
Fixxed it 
I used a relay to isolate the alternator from the ECM when the ignition is turned off. Now, when the key is on and the relay is energized, the alternator is on. When i turn the car off, the relay is open and the alternator is off. I like that this retains the ECM's control of the alternator while running. I don't like that i had to run another two wire loom into the engine compartment, but oh well...
Relay
#87- Alternator terminal L
#30- ECM C2-15
#85- Ground
#86- Ignition Hot
I used a relay to isolate the alternator from the ECM when the ignition is turned off. Now, when the key is on and the relay is energized, the alternator is on. When i turn the car off, the relay is open and the alternator is off. I like that this retains the ECM's control of the alternator while running. I don't like that i had to run another two wire loom into the engine compartment, but oh well...Relay
#87- Alternator terminal L
#30- ECM C2-15
#85- Ground
#86- Ignition Hot
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