LS swap alternator issues - Team Camaro Tech
LSx Swap LSx Engines in Non-LSx Vehicles

 2Likes
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 21 (permalink) Old Jul 14th, 19, 05:03 PM Thread Starter
Senior Tech
Greg
 
Join Date: Aug 2011
Location: nebraska
Posts: 883
LS swap alternator issues

I have a LS376/480 with a 4l70e that I put in almost 3 years ago. I got the Holley accessory drive which came with a 130a alternator. The first one lasted about a year but then went out 1 day. I got another one and it went out in about 100 miles. I turned that one in for warranty and got another. That one lasted me up until about March of this year and it started acting funny so I swapped to a spare. The spare only lasted a couple months and I just put on another this weekend.

At first I thought I may have just had a bad couple alternators because we all know the quality of parts nowadays. There is no way that I could have gone through this many alternators without some other issue.

I started doing some testing and some research. I am going to add a more grounds just to make sure that isn't this issue. I tested my battery wire to my alternator for correct sizing by measuring voltage drop at full load and I am only dropping .2 - .3 volts so that seems fine. I have a brand new optima battery that I put in about 2 weeks ago. At full load at idle (A/C, cooling fans on high, headlights, and stereo with 2 amps on) and I am getting 14.3 volts at the battery terminal on the alternator which is right where it needs to be. So it seems the alternator is fine with the load. Everything is functioning correctly in the car.

Anyone else have any issues or offer any insights?

My 69 Build thread :
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


1995 Z28 (sold)
1987 Iroc-Z (sold)
2005 350Z (sold)
gphusker is offline  
Sponsored Links
Advertisement
 
post #2 of 21 (permalink) Old Jul 14th, 19, 05:34 PM
Gold Lifetime Member
Chris
 
130fe's Avatar
 
Join Date: Feb 2001
Location: Jacksonville, FL
Posts: 1,580
Re: LS swap alternator issues

When it goes out, what symptoms are you experiencing? What harness are you using? Are you using the Holley alt pigtail?

Chris
1968 Camaro SS coupe, Lemans Blue/medium blue interior
LS3/T56 Ridetech Suspension
130fe is offline  
post #3 of 21 (permalink) Old Jul 15th, 19, 05:21 AM Thread Starter
Senior Tech
Greg
 
Join Date: Aug 2011
Location: nebraska
Posts: 883
Re: LS swap alternator issues

When it goes out it the voltage just drops and it just quits charging. I am using the GMPP harness and the alternator connector is built in. Not using the Holley pigtail.

My 69 Build thread :
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


1995 Z28 (sold)
1987 Iroc-Z (sold)
2005 350Z (sold)
gphusker is offline  
 
post #4 of 21 (permalink) Old Jul 17th, 19, 05:26 AM Thread Starter
Senior Tech
Greg
 
Join Date: Aug 2011
Location: nebraska
Posts: 883
Re: LS swap alternator issues

I talked to a bunch of different people (GM Tech Line, PCM of NC who did my fan wiring kit, and a really good local alternator and starter repair shop) and got mixed opinions.

The local shop mentioned I may need a resistor on the "excite" or "L" terminal wire because it is sending too much voltage and burning the regulators out. I only talked to them on the phone and I really doubt they fully understand how the wiring on the car all is because they have never seen it, but still I thought it may be possible. They also mentioned to make sure my grounds are all good.

PCM of NC didn't have much advice other than they had never heard of this happening (they specialize in late model GM stuff). I was mainly questioning them on the fan wiring just to clarify how it all functions.

I placed 2 separate calls to the GM tech line and both people seemed very knowledgeable and both confirmed there is no need for a resistor in the wire going to the "L" terminal with this harness. They said grounds could be a possible issue but also mentioned the possibility that I may have just gotten several junk alternators in a row because that does happen. Getting junk alternators was my first thought, but then when you are on alternator #4 it makes you start to wonder.

So here is where I am at now. I added a couple additional grounds because that really cant hurt. I have a ground from each side of the engine to the frame. From the same bolt on the frame I have a ground going to my firewall. I have ohm checked my body, engine, frame in several spots to make sure there is good connection between them all. So I am going to roll with things and see what happens now.

My 69 Build thread :
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


1995 Z28 (sold)
1987 Iroc-Z (sold)
2005 350Z (sold)
gphusker is offline  
post #5 of 21 (permalink) Old Jul 17th, 19, 06:16 AM
Senior Tech
Lee
 
Join Date: Oct 2011
Location: Texas
Posts: 150
Re: LS swap alternator issues

If you don't have resistance on the "L" terminal then I recommend that you add some. The "L" terminal is used to excite the rotor windings when the alternator is not turning but after the alternator starts turning the alternator will provide its own excitation and it also adjusts the amount of excitation to keep the alternator at the proper voltage. Without the resistance the alternator will have a tougher time maintaining proper voltage since the self-excitation current is back feeding all the way back to the battery. In the original circuit the incandescent bulb in the dash for the alternator provided this resistance. Putting a 510 ohm resistor in parallel with this lamp is a good idea in case the lamp should burn out or if you don't have this lamp anymore.

Another thing I would check is the "S" terminal. This is the remote sense terminal of the regulator and if the connection is intermittent it will cause the regulator voltage to swing high and may cause it to shut down. Although I would think you would see this on the voltage gauge if you were watching for it.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
blitzer454 is offline  
post #6 of 21 (permalink) Old Jul 17th, 19, 06:31 AM
Team Member
Don
 
Join Date: Jun 2006
Location: Mountain Springs, Texas
Posts: 3,960
Re: LS swap alternator issues

I thought the resistance was included in the GMPP harness? At least that has always been my assumption.... I think that is why GMPP tech said no additional resistor is needed.

Don

1969 Camaro LSA 6L90E AME subframe and IRS
1969 Camaro vert LS3 4L65E Ridetech level 2 - sold
1959 El Camino project
1969 Mustang Sportsroof project
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

1956 Cameo project - C5 drivetrain
1957 Buick Caballero project
dhutton is online now  
post #7 of 21 (permalink) Old Jul 17th, 19, 07:35 AM Thread Starter
Senior Tech
Greg
 
Join Date: Aug 2011
Location: nebraska
Posts: 883
Re: LS swap alternator issues

Quote:
Originally Posted by dhutton View Post
I thought the resistance was included in the GMPP harness? At least that has always been my assumption.... I think that is why GMPP tech said no additional resistor is needed.

Don
Yes Don is correct according to GM. The tech said there is no need for a resister because the computer adjusts voltage as needed. Also for reference, I am using a 4 pin alternator with 1 wire going to the "L" terminal. No other wires are used.

My other thinking is there are countless people who have used this exact harness (several on here) and Googling doesn't show me any results for that exact issue. There are enough people on different forums talking about LS swaps that if this was an issue it would have been talked about.

I appreciate the input though. You are 100% spot on for an LS swap where you may be using a wire going to your alternator from a switched 12v source that isn't coming from the computer.

My 69 Build thread :
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


1995 Z28 (sold)
1987 Iroc-Z (sold)
2005 350Z (sold)
gphusker is offline  
post #8 of 21 (permalink) Old Jul 17th, 19, 04:20 PM
Senior Tech
Garth
 
Join Date: Oct 2012
Location: PA
Posts: 1,171
Garage
Re: LS swap alternator issues

How did you rewire the cars front harness with the old voltage regulator and all that stuff? All the old charge circuit and wires should be bypassed and/or abandoned.

Itís been awhile since I did mine but had the same setup, GMPP LS3 and GM harness. I seem to recall my charge wire going to the starter lug, I used that as a junction for the battery since it was in the trunk. Power center ran from there too. I kept everything as short as possible and nothing Ďextraí.

Your engine harness grounds are very important. The engine to frame ground is needed, one good ground. The factory had the subframe then grounded to the body with a strap. You donít need anything more than that.

I donít know where this resistor would go. Charge wire and harness plug was all I remember. Alternators didnít have all the terminals like the old ones. These are internally regulated alternators.

Have you checked to see if your overloading it? Voltage alone wonít tell you that. If it goes out again I would take the alternator to a rebuilder and have them build it and do some post mortem diagnosis to see if the can figure out what failed.

I donít think you go four bad alternators.

1969 Camaro SS 350 LeMans Blue
2015 Z/28 - Red
2 x 1967 R/Tís
1977 Power Wagon
1978 Liíl Red Express
69L48Z27 is offline  
post #9 of 21 (permalink) Old Jul 18th, 19, 05:19 AM Thread Starter
Senior Tech
Greg
 
Join Date: Aug 2011
Location: nebraska
Posts: 883
Re: LS swap alternator issues

Quote:
Originally Posted by 69L48Z27 View Post
How did you rewire the cars front harness with the old voltage regulator and all that stuff? All the old charge circuit and wires should be bypassed and/or abandoned.

Itís been awhile since I did mine but had the same setup, GMPP LS3 and GM harness. I seem to recall my charge wire going to the starter lug, I used that as a junction for the battery since it was in the trunk. Power center ran from there too. I kept everything as short as possible and nothing Ďextraí.

Your engine harness grounds are very important. The engine to frame ground is needed, one good ground. The factory had the subframe then grounded to the body with a strap. You donít need anything more than that.

I donít know where this resistor would go. Charge wire and harness plug was all I remember. Alternators didnít have all the terminals like the old ones. These are internally regulated alternators.

Have you checked to see if your overloading it? Voltage alone wonít tell you that. If it goes out again I would take the alternator to a rebuilder and have them build it and do some post mortem diagnosis to see if the can figure out what failed.

I donít think you go four bad alternators.
All my old voltage regulator etc are long gone. The wiring going to the 4 pin plug on my alternator comes from the GMPP harness. I have a essentially a battery cable going from the back of my alternator back to the battery. Battery is in the front of the car. By overloading I assume you mean that I am pulling more amps than the alternator can put out. I thought of that as well and I don't have anything out of the ordinary electrical wise. LS3 with a 4L70E, dual electric fans (the superior radiator ones), electric fuel pump, vintage air and a stereo with 2 amps and Dakota Digital gauges. If I have any further issues I am going to take my alternator to a local shop that specializes in that and see what they have to say.

My 69 Build thread :
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


1995 Z28 (sold)
1987 Iroc-Z (sold)
2005 350Z (sold)
gphusker is offline  
post #10 of 21 (permalink) Old Jul 18th, 19, 05:50 AM
Gold Lifetime Member
Steven
 
stamatisg1977's Avatar
 
Join Date: Sep 2005
Location: Mastic Beach Village, NY
Posts: 3,072
Back in the day when i used to do car audio there was a formula that we used to determine how much power we needed to safely run the equipment

Later i will dig up some of my books and post it

69 Frost Green Camaro
LS3 with TSP stage 3 cam
Tremec TKO 600
Moser 12 bolt rear with ford ends 3.73:1 Eaton tru trac differential
Speedtech pro touring subframe
Ridetech rear 4-Link


Follow my journey here:

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
stamatisg1977 is online now  
post #11 of 21 (permalink) Old Jul 18th, 19, 08:24 AM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 32,010
Garage
Re: LS swap alternator issues

You might get/borrow a starter current meter, the type of meter slips over the cable, and see how much current is being converted.
Is alternator case hot to the touch? The higher the current demand, the hotter the case.
And, if two ground cables between engine and chassis/body, remove one of them - eliminates ground loop, more prevalent in AC circuits than DC circuits.
The battery is a parallel load in the electrical circuitry of car.
There should be a cable from alt BATT stud to distribution block, usually horn relay buss bar, then power lead to fusebox, and lead to battery junction block.
Yes, I read a cable from alt BATT stud to pos clamp, and may not be a bad idea, but, you might try a resistor in the line like OE design.
Can't hurt.

Give a man a rescued dog for the health of both their souls. May 2017 ROTM Winner - Thank you!
'
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
CUBS - 2016 World Series Champions - Thank you, Joe Madden Ö enjoy your next chapter.
Everett#2390 is online now  
post #12 of 21 (permalink) Old Jul 18th, 19, 05:12 PM
Senior Tech
Garth
 
Join Date: Oct 2012
Location: PA
Posts: 1,171
Garage
Re: LS swap alternator issues

Resistor in what line?

1969 Camaro SS 350 LeMans Blue
2015 Z/28 - Red
2 x 1967 R/Tís
1977 Power Wagon
1978 Liíl Red Express
69L48Z27 is offline  
post #13 of 21 (permalink) Old Jul 19th, 19, 08:15 AM Thread Starter
Senior Tech
Greg
 
Join Date: Aug 2011
Location: nebraska
Posts: 883
Re: LS swap alternator issues

Quote:
Originally Posted by 69L48Z27 View Post
Resistor in what line?
Alternators need some sort of resistance in the "excite" line or on the style of alternator I have the "L" terminal if they are wired directly to a switched 12v source. This resistance can take a couple different forms. You either need an "idiot" light or a resistor that provides the same amount of resistance as the bulb would.

That all being said, according to the GM tech line claims that the GMPP engine harness (that has a "Gen" plug for the alternator build into it) doesn't need a resistor because the signal is coming from the computer and not just a switched 12v source. From my understanding the reasoning for the resistor is that the voltage from this "L" terminal would be too high and cause the regulator to overcharge and thus burn out the regulator.

My 69 Build thread :
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


1995 Z28 (sold)
1987 Iroc-Z (sold)
2005 350Z (sold)
gphusker is offline  
post #14 of 21 (permalink) Old Jul 19th, 19, 08:28 AM
Moderator
John
 
Vega$69's Avatar
 
Join Date: Sep 2010
Location: Vegas NV/Wesley Chapel FL
Posts: 13,287
Garage
Re: LS swap alternator issues

Iíve used the GMPP harness at least 6 times or more and all builds still have the alternators I installed running without any problems.

2017 Corvette ZO6 with ZO7 Option
66 Chevelle Protour LS3/525(SOLD AT Mecum 2018)
69 SS396 Cortez Silver(SOLD)
69 Z28(Sold)
69 Pro Tour - LS3/T56
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
(SOLD)
69 Pro Tour - LS7/T56 (SOLD)
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

69 Z28/RS Tribute355/5 Speed (SOLD)
69 RS Clone 427/TH400 (SOLD)
67 RSZZ502/5 Speed (SOLD)
69 Camaro 406 SBC/TH400 (SOLD)
Vega$69 is offline  
post #15 of 21 (permalink) Old Jul 19th, 19, 08:28 AM
Senior Tech
Kip
 
Join Date: Sep 2004
Location: Tulsa, Ok
Posts: 509
Re: LS swap alternator issues

I just went through this with my Holley Mid-mount serpentine belt set up on my LS3. You NEED that resistor...

1967 SSRS
kv67ssrs is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Team Camaro Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.



Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome