backlash2032

Hey! I'm trying to figure out why my charging system has been giving me fits. It's a 2006 base model m6, I bought it with 67k miles on the clock, essentially bone stock. When I bought it it charged perfectly, never dipped below 14.4 volts. As I racked the miles up, I started to get the balancer wobble, and I figured if I was going that far I may as well put a cam in it. So on went a powerbond 10% underdrive pulley, BTR stage 2 n/a cam, their dual springs, and hardened pushrods. Also added stainless works 1 7/8ths long tube headers. Ever since this, It seemed to never charge the same. At idle it would dip down to 12.8 volts or so, driving down the road it would charge around 14 volts. Just chocked that up to the underdrive pulley without really thinking about it. Somewhere along the line, I also added a Nitrous Express plate kit, with a FJO mini progressive nitrous controller, but the issue happened before this anyway.

Fast forward to recently, 108k miles on the clock and the OE alternator completely gives up. Replace it with SEVERAL parts store alternators before i finally bite the bullet and put an AC Delco alternator on it. That one has survived a couple thousand miles and several months so far. The parts store alternators would only last a week lol. That being said though, it seems like my voltages are dropping faster and faster. Now at idle it will dip down to 12.5 volts or so and driving down the road it barely cracks 13.5.

So here are the tests I've performed. I did a voltage drop test on the positive side of the charging system, and I get a pretty consistent .2 volts of drop. Doesn't seem to make much sense as at idle I'm only charging at 12.5 volts. Decided to double check that that was accurate by using some jumper cables and jumping the positive lug on the alternator to the positive terminal of the battery, and noticed no appreciable change in battery voltage. Did the same thing, but jumped the alternator case to the negative terminal. No appreciable change.

I then checked the actual output of the alternator compared to battery voltage. It seems that battery voltage fluctuates the most with temperature. So on todays cool day, idling with the hood open, I was getting about 14.0 volts out of the alternator and 13.6 at the battery. I also checked the voltage at the 3 wire connector at the alternator. One pin had battery voltage, the center pin I'm presuming is a ground as it had 0 volts. And the other pin had 4.80 volts.

I've also checked all engine bay grounds, cleaned, greased, and tightened them. Have done the same with all the positive side connections as well. I also took a good look at the starter solenoid as these are prone to cracking when you add in the heat from long tube headers. Both terminals seem very solid. I wasn't very keen on pulling the starter and taking a closer look, as I have to pull the drivers side header to get the starter out.

At this point I'm absolutely completely stumped, I don't know where to go from here, and so i'm hoping that somebody has some excellent advice for me.

Thanks in advance
Justin

Dano523

Here's your problem, and with the alternator spinning slower at idle, it may be the reason that your not getting 14.7v at the alternator when the motor is idling, and the A/C shut off.

Or could be after market spark plugs and wires that is causing RF noise from the coils back to the ECM, which controls the output voltage of the alternator as well.

As for quick run down with the car idling and the A/C lights off, should have 14.7v from the back terminal of the alternator(under the rubber boot) to the body of the alternator with the meter, 14.5 at the battery, and also at the fuse box terminal to either the negative of the battery or the alternator body, and DIC should be showing 14.1~14.3 volts.


As for clean up of the alternator, below thread link will cover that, but it not your real problem, but isntead under drive pulley and maybe RF noise as well.

https://www.corvetteforum.com/forums...nator-fix.html

SladeX

Being a m6 and cammed now, did you raise idle rpm to keep a stable idle? Auto cars usually idle 600 rpm in gear and still generate enough voltage with a stock alternator. A cammed m6 doing 800rpm idle would negate a 10% drop in rpm, my cammed ls3 does 850rpm idle with a 25% underdrive and gets 13.8v idle
Its posible your setup is frying the rectifiers in the stock alternators. This would drop the idle voltage but seem normalish if the rpm goes up. If revving the engine up brings your voltage up to 13.5 or better when its dropping at idle, thats a good indicator. The bit you noted that when cool seems to have more voltage is also pointing to that. Stock setups run very hot under the hood and a set of longtubes would just really make things hot. My stock ls2 killed an alternator on a super hot day that way. I replaced with a billet tech alternator 170amp which is much better designed electrically to deal with heat.

Turbo6TA

I think your biggest mistake was to install an underdrive harmonic balancer.

The HP increase is so insignificant using an underdrive HB, that it's not worth the problems associated with a slower turning alternator and water pump.

backlash2032

I'll have to look into the cleanup of the terminals in the alternator. Didn't think I'd run into that issue with a brand new re man alternator lol. But as for the plugs and plug wires, that was my first thought as I had NGK TR6s in it. Changed to BR7EFs and had zero change. Also have stock plug wires. Made sure that the positive terminal coming off the alternator is as far away as possible from the #1 plug wire as well.

Idle RPM is 800-850, which negates the 10% underdrive. Longtubes are also ceramic coated, which helps a bit with the heat. That being said, my buddy with a 80k mile cammed auto LS2 car hits 14.0+ all day long with bare stainless headers lol

SladeX

Its hit or miss with the stock alternator. Being on my 2nd c6, I just brought over the billet tech I had to it and keep a working stock one as a spare. On the old one, it was when cleaning it as per the above post that I found the fried rectifiers.

Dano523

Guess, I need to add replacing fired bridge rectifiers to the post now as well. A brand new bride rectifier assembly plate is only about $30 for the valeo units, and is a snap to de-solder and solder in the new one,
Attachment 48332766


or you can replace just the burn bridge rectifier in the assembly that is bad for a few bucks isntead (mouser has them).

backlash2032

SladeX

When the rectifiers started going out on my alternator, I noted that when at idle it would be 12.x V and while driving it was 13.4. Eventually that idle dropped to 11.9V at idle cold/hot which was insufficient to power everything.

If revving the engine at idle raises the voltage to 13 again, your alternator rectifiers are on the way out. Replace/repair or get a better built alternator. I got the billet tech one years ago and have not had it drop below 14V at idle even on the hottest of days and crazy humidity this year.

backlash2032

backlash2032

Tally Ho

Check your starter leads. I just fixed a 2008 with the same type of charging issue. New alternator and battery did not fix the problem. The stud on the starter that the hot leads connect to was not making contact. The plastic housing was cracked and the stud was making intermittent contact. When it finally disengaged, the car would not start. Required a new starter and now everything in the charging system works fine. It's worth a look especially with your mileage. The car I worked on had 96K miles.

backlash2032