So long story short Ive got a project at the shop, LS3 Erod, nothing special, all stock outa the box. It overcharges. Soon as you start it it charges 16-17 volts, rev the motor it spikes to 19+.

Engine is properly grounded, alt the cables have less than .1 voltage drop. I swapped the alternator and the ECU with new ones right out of another Erod we have sitting here in the box, same thing. I ohmd the wire from the L terminal on the alternator back to the ECU, pin 7 grey connector E67 ECU. Its fine, I can command the L terminal on and off with a scanner and the alternator charges and stops charging like its supposed to in the test mode, and the ECU sees the correct voltage in the data stream, 17v and up. I have 5v on the alternator plug with it unplugged but I havent checked the duty cycle with it plugged in and running. This is a PWM triggered alternator.

What the hell am I missing here? First one Ive had do this, all I can figure is there is something going on in the harness im missing, though its unlikely cause I can command full field and no field with the scanner. Or something like a ground isnt pinned right at the ECU connectors? This is just too wierd at the end of the day on a friday haha. Any thoughts at all?

 

Does that harness use a "sense" wire on the "S" terminal? If so, where is it wired to? If there's a wire on the "S" term and it's not attached, it could be reading stray voltage (or even ground!) and driving the output high.

 

Are you sure that the harness and ECU are set-up for PWM control? There was some confusion in a recent thread about this...

http://www.lateral-g.net/forums/showthread.php4?t=55174

Andrew

 

It's an erod set up. I've done about 15 of these at this place and never have I had one do this. It's got 1 wire from the ecu to the alt plug at the L terminal, same as very other one I've done, and the battery cable at the lug. So far as i remember every other one including the one I just unboxed has a single wire on the L terminal. I can command the ecu to go full duty cycle on or off and the alternator responds accordingly. I thought you couldn't do anything with alternator control in HP tuners...is there an setting for generator control on or off? I read that thread but he had an alternator mismatch. Mine is all matching

 

Internal regulator is being commanded by ecm, try disconnecting the field wire plug while its running for 30 seconds then plug it back in and see what your system voltage reference says, you could just ave and uncontroled reg because it's bad. Also, I had an field exciter wire in the wrong position of the plug, after that was determined and relocated it worked fine, this was a no charge condition.

 

I swapped the alternator and the ECU and i've verified pin position on another harness right out of the box. Disconnect the wire it stops charging reconnect it and it just spikes and stays full field. I have the Erod fuse box connected to the terminal on the back of the alternator, it was just extra convenient with the location of everything in the engine compartment of this build. So battery to starter to alternator to E-rod fuse box. I wouldn't think this would be an issue, Ive seen and used Howell LS harnesses with the E-fan wiring in them and they take power right from the alternator terminal to run the fans, never had a charging issue with those. But for kicks im gonna relocate the power wire for the fuse box temporarily. After that im gonna call up my tuner and bring him the ECU to see how the alternator settings are done. From what I read at least with an E38 ECU there are a few alternator settings in system options

 

You should just try to run straight 12v to the exciter wire terminal on the alt. to see what the system charges at, if you have normal charge voltage 13-14V then you know where your problem is.

 

This particular alternator doesnt work with a regular 12v to the exciter. Its a PWM signal from the ECU. Had my tuner come down and we looked at and played with the alternator settings for over 2 hours. I have one other vehicle here thats identical drivetrain wise thats running with no issues, and whats crazy is inside the alt. settings, its all disabled. I cant borrow any parts from that vehicle as its sold and detailed. At this point im gonna assume its a problem within the harness and put a 1 wire alternator on it. Swapping the engine harness is a nightmare and the time/cost doesnt warrant it at this point. I hate to throw in the towel but after swapping 2 alternators and 3 ECU's, granted they were out of the box and not on running vehicles yet, I can only assume its in the harness, even though the single wire to the plug on the alt is pinned correctly and is working as the ECU can turn the alternator on and off. I have 5v at the plug disconnected and something like .46 when its plugged in. It commands 99.6 duty cycle all the time on the vehicle thats working fine as well as this one, but this one is not happy.

It has a 4 pin plug but only has an L and F marking on the plug. Its a DR44G I think, the regulator so far as I know is setup for PWM only. Id be happy to just hook up switched ignition to it if that would work but the 25888970 alternator I dont think would like that, unless someone tells me otherwise. I know the regulators that have PLFS I can get away with a switched source, but this is only L and F

I have to add this to my very very short list of cars I couldnt fix, not for lack of trying, but for time and cost reasons...bummer. But the vehicle will be here for a little while still while we do our test miles.

 

So i put another harness in it for kicks and an ECU from a knows working charging system, same thing, full field and overcharges soon as you start it. Changed the battery also, same thing. Im seriously puzzled here. Only thing I havent done is put a 3rd alternator in it or connect it straight to the battery instead of the the starter. Guess Ill try that tomarrow

 

Isn't the PWM signal voltage from the ecm? Try unplugging it while it's in the overcharge state and get your DVOM and get a read on that exciter wire, find out what you,ve got there, compare that reading to what the other like vehicle setup's exciter wire.I f it's the same, try a different alt, If it's radically different then there's a clue for you. Be 101% sure the field wire is in the correct position on the alt and at the ecm and there's continuity to and from. None of this should take days to solve if you're diagnosing by deduction/comparison if you're lucky enough to have another setup in the shop.

 

It's hooked up to the L terminal on the alternator like every other one I've done. 5v unplugged at the alt connector like it should have. Engine running. Plug it in it goes to .46 v. The car I have working properly has 1.3 v running plugged in. Something is commanding the ecu to do this and I have no idea what. Only thing I don't have plugged in is the oil pressure sensor. That should have no bearing on the charging system. I put a resistor in it to simuate oil pressure anyway and it didn't change

 

Is it possible it's connected to the wrong pin? In the pin out diagram I have pin 7 is a purple wire labeled "generator regulator control"...

Further down, pin 29 is the gray wire labeled "generator field duty cycle signal".....

The fact that you can cycle the charging circuit shows it's good, but it doesn't help you regulate the output voltage of the alternator.....just a guess..

T,

 

A brief cut and paste from a search, see if this makes any sense. It kind of does, but seems it would need a wire back to the ECM to monitor duty cycle.


System Operation
The basic operation of the RVC system is
covered here, but not all systems will enter all
modes of operation; refer to the applicable
service manual information for more details.
The purpose of the RVC system is to maintain
the battery state-of-charge at 80% or
above and support vehicle loads.
The six modes of operation include:
• Charge Mode
• Fuel Economy Mode
• Voltage Reduction Mode
• Start Up Mode
• Windshield De-ice Mode
• Battery Sulfation Mode
The PCM/ECM (generator battery control
module on full-size trucks) controls the generator
through the generator L-terminal control
circuit. It monitors the generator performance
though the generator field duty cycle signal circuit.
The signal is a 5 volt PWM (pulse width
modulated) signal of 128 Hz with a duty cycle
of 0-100%. Normal duty cycle is between 5-
95%. The ranges between 0-5% and 95-100%
are for diagnostic purposes. The accompanying
table shows the commanded duty cycle
and output voltage of the generator.
The generator provides
a feedback signal
of the generator load
through the generator
field duty cycle signal
circuit to the control
module. The signal is
a 5 volt PWM signal of
128 Hz, with a duty
cycle of 0-100%.
Normal duty cycle is
between 5-99%. The
ranges between 0-5%
and 100% are for
diagnostic purposes.
Charge Mode – The control module enters
Charge Mode whenever one of the following
conditions is met:
• Under WOT conditions and when the fuel
rate (sent by the ECM/PCM) is greater
than 21 g/s and the throttle
position is greater than 90%.
• The headlamps are on, low or high beam.
• The wipers are on for more than
8 seconds.
• The electric cooling fans are on
high speed.
• The rear defogger is on.
• The Battery SOC (state of charge)
is less than 80%.

Here's the table...

Duty
Cycle
Generator
Voltage
Set Point
10% 11.0V
20% 11.56V
30% 12.12V
40% 12.68V
50% 13.25V
60% 13.81V
70% 14.37V
80% 14.94V
90% 15.5V


T,

 

Some explanation at post #21...

https://ls1tech.com/forums/conversio...-wiring-2.html


T,

 

Ive found and read through all that haha. The thing is the E-rod setup/control pack for an LS3 from GM performance does not have alternator controls turned on in the ECU. Nor does it have that grey wire for field sense, yet the systems still work perfectly. How? Id love to know cause I cant figure out how. I did trace the L terminal wire back to pin 7 right where it should be, and the likeliness of it being wrong in 2 harnesses is unlikely. I took a chance and hooked up what would be the S wire to battery voltage, and it charges at 14.6 now. Im fine with that. Took it on its maiden drive and all seems normal with the charging system. I dont know what the deal was but it seems to be stable. Building an arduino is something I would do with my own car, but not something I wanna do in this case with a clients car.

I wish I knew how the setup was supposed work with the LS3 GMP controls pack, then maybe I could further diagnose. But at this point, i went down every path I could think of, replaced every part I could, and seeing in multiple ECMS the alternator control turned off, makes it even more mysterious how the E-rod ECU is supposed to handle the charging system.

 

Have you called GMPP?

Andrew

 

Getting a hold of anyone at GMPP is an effort in futility, in my expirance anyway. I fixed the issue by adding a wire from what I think would be the S terminal t the battery lug on the alternator for a reference voltage. Maintains 14.6v. Ive had this issue on GM Erod crate motors now, I dont know why, but thats what fixed it and I moved on.

 

I had exactly the same problem with my own motor and wiring harness this summer, i had new ls3 whit gm wiring harness, finally the matter was resolved by local GM dealer and he had discovered that several wiring harnesses had a factory assembly fault in GM factory. I don't know which cable place they had replaced in the wiring harness but it started to work perfectly.