OK folks, I feel like I have been chasing a ghost (gremlin) with my car. The car is far from stock and I am running Speed Density because of an earlier cam choice and reversion issues at the time. I stuck with SD out of simplicity and cost with my new cam upgrade (details in sig).

In short the car would not hold timing. What I mean is: the car would start out with a respectable timing but over time something would command more and more advance even beyond 40 degrees and consequently more KR as the timing advanced. My tuner and I have been using HP Tuner to capture logs. Nothing jumped out at us until I noticed during high speed transitions (Shifts) the voltage gauge on the car was reading below 13 volts and even at times below 12 volts.

I am sourcing an alternator (although GM Manual calls it a generator) but could this be the cause of this KR and persistent timing advance? Keep in mind all of the ignition components are stock LS6.

Feedback and thoughts are welcome

 

I have been chasing electrical gremlins down for a long time now on my F-body. Not holding a tune, timing issues, maf issues ect. ect. I logged my volts and it always seemed to have around 12.8 or a little lower and I always chalked it up to the underdrive pulley and the battery being located in the back. I figured the alt. always was charging somewhat and it never left me sit and always started so it must have been fine, right? Well i finally threw a new highoutput alternator in and WOW, what a differance. 14.2 volts + and it just seems to run alot better. I would get that alternator checked or switched out to take this out of the equation. You'd be surprised how fussy the electronics are now and the need for the right amount of voltage.

 

Interesting, I have an underdrive pulley also, a TVS 1900 SC. I have been having knock/timing issues and my dash lights up with the same error under certain conditions (one of the MAP/MAF errors, I forget). Normally while driving at low RPM's then coming down on it the dash would light up. If I shift to a lower gear, getting the RPM's higher then coming down on it no codes are thrown. I have noticed my voltage was a little low at low RPM's.

I went with colder plugs and meth and it seems to have taken care of the knocking it but my dash is still lighting up.

I was thinking about getting the Cartek flip drive to get the accessories back to normal speed and to dedicate the SC to the UD pulley.

Now I will be keeping a closer watch on my voltage, thanks ramairws6 for your info.

 

I have the SLP UD pulley as well. So the answer may be to find a pulley for the alternator that is 25% oversized. Although if I remember correctly my voltage did not change all that much, if any, at the higher RPMs.

Has anyone seen over-drive pulleys for accessories? Kinda defeats the purpose of the UD pulley to begin with

 

Ok folks just ordered an alternator over-drive pulley from Thunder Racing. I am going to see if that corrects the problem. Although I suspect the roadracing, Texas heat, (me forgetting to disconnecting the battery and shorting out the hot lead to the alternator housing ) has taken it's toll on the stock unit. I will grab some logs and see what timing does with the OD alternator pulley.

 

I think that over-drive pulley will help the alternator get back to the normal RPM.

I need to go a different path due to my SC, I am almost ready to order the Cartek Flip-drive. I will do some voltage checks this weekend to get a baseline. The cartek solution uses the A/C part of the balancer to spin the accessories which is smaller and will make the accessories spin faster.

http://www.cartekracing.com/Products...EFlipDrive.htm

I realized today I have installed a MSD boost a pump and gauges which add up to 35 amp draw to an alternator that is marginal for stock use as it is, I am looking for a higher output alternator now.


Mike, let us know how the pulley works for you.

 

Hey Mike,

FWIW, I run a 10% UD pulley and don't have any problems and that's with running a 1000w audio system.

Kevin

 

Kevin,

Now you have me wondering what mine under drive is; I thought it was higher than 10% but now I am not so sure.

I am working on putting a dinky system in my car but I need to verify capacity before I go that route.

Ok I just checked and mine is 25% under-drive.

 

I drove my Vette to work today and the voltage on my display showed 14.7 when I started it, dipped to 13.8 while driving, bouncing around a little but nothing drastic. I made a short trip later in the day and when I got back to the parking lot my voltage dropped to 12.2, a 17% drop in voltage, anything under 13 volts I consider bad. Hopefully this weekend I can do some checking to see what else I can discover. Since I am losing more than two volts, I am assuming this could affect other sensors. I image the 5 volt sensors have a tighter tolerance and will not be as forgiving with low voltage.

 

Sorry to bore you guys with another update. I rode home tonight and I was watching the voltage and is was steady 14.2 volts. I normally can hammer it at low RPM and sometimes throw code but with the voltage steady at 14.2 tonight i couldn't get it to throw the code tonight. Now I am thinking it isn't a pulley issue but something random like loose cable somewhere or alternator dying.

 

2002 Corvette:From the GM manual.

GM calls it a generator because Chrysler owns or did own the trade name and GM would have had to pay them royalties if alternator was used in the manuals. A little worthless trivia.

Charging System Description and Operation
Generator
The Valeo generator is electrically similar to earlier models. The generator features the following major components:

The delta stator
The rectifier bridge
The rotor with slip rings and brushes
A conventional pulley
The regulator
The pulley and the fan cool the slip ring and the frame.

The generator features permanently lubricated bearings. Service should only include tightening of mount components. Otherwise, replace the generator as a complete unit.

Regulator
The voltage regulator controls the rotor field current in order to limit the system voltage. When the field current is on, the regulator switches the current on and off at a rate of 400 cycles per second in order to perform the following functions:

Radio noise control
Obtain the correct average current needed for proper system voltage control

At high speeds, the on-time may be 10 percent with the off-time at 90 percent. At low speeds, the on-time may be 90 percent and the off-time 10 percent.

Circuit Description
The generator provides voltage to operate the vehicle's electrical system and to charge its battery. A magnetic field is created when current flows through the rotor. This field rotates as the rotor is driven by the engine, creating an AC voltage in the stator windings. The AC voltage is converted to DC by the rectifier bridge and is supplied to the electrical system at the battery terminal.

When the engine is running, the generator turn-on signal is sent to the generator from the PCM, turning on the regulator. The generator's voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator. When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the regulator varies the field current by controlling the pulse width. This regulates the generator output voltage for proper battery charging and electrical system operation. The generator F terminal is connected internally to the voltage regulator and externally to the PCM. When the voltage regulator detects a charging system problem, it grounds this circuit to signal the PCM that a problem exists. The PCM monitors the generator field duty cycle signal circuit. The system voltage sense circuit receives B+ voltage that is Hot At All Times through a fuse link that is connedted to the starter.. This voltage is used by the regulator as the reference for system voltage control.

Charging System Indicator(s)
CHARGE SYSTEM FAULT
The IPC illuminates the CHARGE SYSTEM FAULT indicator in the message center when the following occurs:

The PCM detects that there is a problem with the electrical charging system. The IPC receives a class 2 message from the PCM.
If the tachometer is less than 500 RPM and the power mode state is in the crank mode then this message will not be displayed. Instead the CHECK GAGES indicator will illuminate.
HIGH VOLTAGE
The IPC illuminates the HIGH VOLTAGE indicator in the message center when the IPC detects that the ignition is in RUN and battery voltage is greater than 15.75 V for more than 5 seconds.

LOW VOLTAGE
The IPC illuminates the LOW VOLTAGE indicator in the message center when the IPC detects that the ignition is in RUN and battery voltage is less than 10 V for more than 5 seconds.

 

Well I bit the bullet and ordered a 150A unit (stereo plans). The KR and timing issue just started with mine and, as stated above, Corey (Henderson Performance) and I were scratching our heads trying to figure out what the hell was causing the car to advance the timing so high. To the point it was causing low RPM, high load (WOT) pinging and, consequently, significant KR.

Additionally, I was getting a flat spot on light acceleration around 2k RPM and milegae wasn't that great either. Although with 465+ RWHP who cares about mileage?

And on top of all of that my poor Optima Red top was taking a beating and needed to sit on a slow 2A charge for days to get its reserve back

SO in a nutshell, I believe, as others do, the electronics for the LSx motor are highly sensitive to voltage dips and needs a consistent feed. I am not sure what the minimum is but I suspect it is in the high 13.x range. If I had the time I would like to narrow down exactly which sensors are the most sensitive. Probably something in the ignition and fuel injection circuit.

 

Doing some Google searching today, I came across guys with headers, which I have and with your mods I expect you might have also. Anyways, they have noticed good voltages until the car gets hot then the voltages drop. Believe it or not but I found several cases of the starter solenoid connection causing the problem. Apparently the solenoid connection is between the battery and alternator, if the starter solenoid connection is altered it affects how much power gets to the battery.

If this is a problem a couple of things can be done. Heat shield around the headers and or starter. Another option would to install a battery relocation kit and bypassing the starter solenoid connection.

Something else to consider.

 

Ok alt is installed with an overdrive pulley; literally took about 10 minutes and five of those was spent trying to find my @#$^%* wrenches.

Finding a belt that worked with the UD pulley and OD alt pulley proved to be a handful and I am not completely satisfied as it was extremely tight getting it on the Katech tensioner but the tighter the better right? I might go with a gates K060770 to get a little more slack. I didn't think the difference between 76 7/8 and 77 1/2 could make that much difference on a belt.

Anywho the alternator is rock solid at 14.2 volts. I need to find an amp meter to measure the amperage. I will drive and log over the weekend and report back. Here's is hoping I can put this demon to bed

 

Glad to hear you are solid at 14.2, if it holds up for you this weekend I will be ordering parts to upgrade mine. Thanks for your posts.

 

Awesome.....it really sucks to be always chasing electrical issues like this. Very time consuming. Glad ya got it worked out. I tell ya what though, i am so happy after installing my new high output alt. Wish i would have bit the bullet long ago! Live and learn i guess.

 

Took the Vette out for a little cruise and the voltage did not drop below 13 volts. I am pretty happy so far and with a couple of WOT to 60 mph I could not get any KR. So far so good.

 

GREAT news Mike.

 

Well after a nice cruise into work this morning and an extended logging session, I can say the KR issue seems to be abated for the moment and voltage never dropped below 14 volts.

My timing is still advancing itself so I need to dig a little deeper on that one

So in a nutshell, I replaced the alternator with a 150A unit, replaced the alt pulley with an OD pulley. As a consequence I had to replace the serpentine belt as well. So for less than 5 bills I now have a charging system capable of supporting the 25% UD crank pulley and support future stereo upgrades.

 

I have the Powerbond 25% underdrive pulley on my 441 and after the new HO alt. everything is mint