Rep Power: 0

Well, I am in a (serious?) situation now. I don't know what's wrong with my electrical system, but here is what I experienced:

1. Start the car, either cold start or warm start, the voltage is around 14.0V, read from VAFC-II and capacitor(all number shown below are read in VAFC-II).

2. Press the acceleration pedal at neutral stop, the voltage stays constant.

3. Start driving, when I press the pedal(gently), voltage drops down to 12.3V.

4. VTEC engages, hard acceleration(full throttle), drops to 11.8V.

5. Lift off the pedal(still in gear, not neutral), voltage goes back to 14.1V.

6. Constant speed with pedal depressed, voltage is 12.3V. After a while, it pops up to 13.8V then back to 12.3V.

7. After all kinds of driving, to a complete stop, after 1 minute of idle, it goes to 14.0V again.

Interesting thing is, when I turn on the AC, voltage is constant at 13.9V, either crusing and accelerating. Only drops when the car is at idle (12.6V) and, if AC is turned on when idling, 11.8V.

Can anybody tell me what's wrong with it?

 
Rep Power: 0

do you have the stock alternator? Sounds like the alternator belt is slipping during hard acceleration, but moving fine at idle.

 
Rep Power: 0

Yes, I have stock alternator. But it only happens sometimes, I will go check tomorrow. It's back to normal now(idle 12.5V and driving 13.9V).

 
Rep Power: 328

Is this voltage reading being taken at the cap? Or are you reading close (within 18 inches or less) of the battery?

 
Rep Power: 812

Um that's normal man. It will even vary due to weather (cold/hot), but our alternator charging system has an ELD (electronic load detector) that shuts off power when there's no need for it. Try turning on the fan when the voltage is low and I bet it will go back up. When it's really cold, it tends to stay high sometimes even over 15v when first started.

 
Rep Power: 328

Again, I'd like to know where the voltage reading is being taken from? Accessory wire, or the cap, or at the battery? If you were to take it at the battery, within 18 inches, I'd be willing to bet you it stays at a constant voltage, or fluctuates a few points, but not a full number.

 
Rep Power: 812

I took mine from a separate voltmeter, which I had hooked directly to the battery. I got the same results using the vafcII volt reader wired off the ecu power wire.

 
Rep Power: 328

Not you gearbox, the 82801 guy that started the thread. lol

 
Rep Power: 0

I take both of the readings from VAFC-II connected to ECU and on the cap. They are consistent, but the cap's reading is a little higher than the VAFC-II.

 
Rep Power: 328

That's wierd that the cap stays higher. I'd have figured it the other way around due to line loss.

 
Rep Power: 0

Ok whatever it is now. I got an Optima Yellow Top. After I drop the battery in there, VAFC-II shows L->H 3700rpm(!!) in V/T info. What's wrong with it? It was showing 3250rpm before.

 
Rep Power: 812

Interesting. Mine always shows around 3200rpms. Did you do the idle learn procedure after changing the battery? Prolly not a big deal.

 
Rep Power: 0

No, it shows 3700 but the engine still engages at maximum 3250, so not a big deal.