Ok guys so ive got a 2001 civic ex 5 speed coupe and im having some very weird electrical issues. I have about 1300 watts of stereo equipment on my stock alt and battery, i know this is very sub par. I have the big 3 done, which is 0 gauge wire from alt to battery, battery ground, and engine block ground. When i drive around sometimes the car drives around at 12.5 volts give or take .2 volts or so. At first i thought it was the equipment so i took it out and it still does it. A bolt had come out of the alt which made the belt loose so i fixed that problem last night and the problem still persists. Ive tried a different battery that is known to be good and problem still persisted. All grounds that i have made with the 0 gauge wire and for the amps are good, ive tested each one. I went to all 3 major parts stores, orielys, advanced, and auto zone, they all said the alt and battery checked out ok. If the alt checks out ok then what could be the problem? Ive tried everything, even undoing the big 3 and rehooking up the tiny *** stock wires.

When i drive on the interstate the problem does not occur the car drives at 14.4 volts as long as im 3k + rpms. After getting off the interstate or slowing down to ~50 the voltage drops. The voltage also drops whenever i hit the gas driving around town, if i leave the car in gear and let off the gas the voltage goes back up to 14.4, but as soon as i accelerate the voltage drops. The problem doesnt occur every single time i drive but it does happen often.

Some say it could be the pcm but why doesnt it do it constantly if its the pcm?

Any ideas or insight would be great.

 

I always thought this is a gas-saving feature. The alternator shuts itself off when the load isn't high, then comes back on when necessary, or when engine load is low. I have a completely stock 2005 ex coupe and it does the same thing.

 

That's inaccurate. Your alternator should never shut itself off. It doesn't have a clutch or any mechanism/control to reduce electrical current.

 

I disagree, I believe the alternator can shut itself off and Civics have this feature. I don't have any direct sources, but this thread mentions the Civics existing "smart alternator" and details a method for creating a switch to manually switch the alternator off for increased fuel efficiency: http://ecomodder.com/forum/showthrea...8-a-20513.html

That thread is specifically about a 6th gen Civic but I'm sure the mechanism is similar for the 7th gen as well. I've observed the voltage on my car while driving for several years now and I can see a consistent pattern for when it switches off and back on. I've had my alternator rebuilt for non-related voltage spikes and observed the same pattern before and after.

 

Here's a blown up diagram of the alternator:


Those four pins are for the voltage regulation. You may see current draw fluctuate, which is typical for any alternator when the RPM's change. But, to avoid spikes hitting your car's electrical system, the voltage regulator is put into effect. If you look closely in the diagram... you'll see there is absolutely NO CLUTCH. Meaning, at any given time, the alternator is creating electricity. Its directly driven by your crank pulley, so it is ALWAYS spinning.

 

Aight thanks man. A guy on one of the car audio sites i look at said that he had the same problem and his internal regulator was fried. I was going to put a high output alt in either way but looks like its gonna be now instead of later, lol.

 

You're right about it not having a clutch, I was mistaken in saying that the alternator shuts off entirely. That doesn't change the fact that the voltage drop is an intentional feature meant to increase fuel efficiency. From the 7th gen Civic repair manual on All-Data:

2005 Honda Civic L4-1.7L SOHC Copyright © 2009, ALLDATA 9.90 Page 1
Alternator: Description and Operation
Alternator Control
The alternator signals the engine control module (ECM)/powertrain control module (PCM) during charging. The ECM/PCM then controls the voltage
generated at the alternator according to the electrical load determined by the electrical load detector (ELD) and driving mode. This reduces engine load
to improve fuel economy.

2005 Honda Civic L4-1.7L SOHC Copyright © 2009, ALLDATA 9.90 Page 1
Electric Load Sensor: Description and Operation
Electrical Load Detector (ELD)
Since the early 1990's, Honda vehicles have come with an electrical load detector (ELD) unit in the under-hood fuse/relay box. This unit allows the
ECM/PCM to regulate the alternator (switch it between high output and low output) to provide the best combination of fuel economy and electrical
system operation. The ELD sends a signal to the ECM/PCM that's proportional to the electrical demand. The ECM/PCM switches the alternator between
high output and low output depending on several factors, which include electrical demand, battery charge level, and the driving cycle. When the
alternator is in low output, the engine load is reduced and fuel economy improves.