I've been having a hell of a time figuring this out.

Had a problem where the alternator would not charge the battery at all. This was apparently a corroded plug... cleaned it out, and voila! The car worked great.

While delivering tonight... I get my infamous clock-LED dimming... you should have seen the look on my face.

This time however... the system did not discharge. I was able to start the car up after a couple cranks. So, the current status:

While driving, the system charges... clock is bright, windshield wipers function normally, etc. When I brake or idle, the system... discharges. clock dims, windows barely roll up down, etc. When driving, no battery light. When at a stop light/idle, the battery light comes on.

I am asking for some technical help.. what the hell could this be? I've already swapped alternators and batteries. It's not those.

 

I hope you know how to use a multimeter. It's time to trace your voltage flow and look for voltage drops. I would start at the battery. With the engine running, you should see around 14.4V at the battery terminals. If battery voltage is 12.6 volts or lower, then your alt. is shot. Voltage needs to be higher than 13.6 volts at the battery, or it will not charge.

If all is well there, then go to the battery cable coming out of the alternator, which should be fairly easy to access on the 3rd gen Preludes. Check for voltage there with the car running, should see 14.4V. If not, ALT SHOT. If 14.4V is there, then I believe that wire goes to the underhood fuse box. If you follow the positive cable off the battery, that should be going to the same place. There, again, check for voltage. A wiring diagram would help.

So simply put, you have a voltage drop somewhere. Where? That's what you gotta find out. Don't know how to use a multimeter? Bring your Prelude to a shop, they'll probably do less damage than you.

Good luck man.

 

Thanks d00d. I'll take a multimeter to the system tomorrow and start checking it out. Much appreciated.

 

Ok, after cold idle, the battery reads: 8.3-8.5v. The terminals read 9.7v.

The interior clock is dim. When I push the gas pedal, it brightens up. I need to get a second person to gas the car while I hold a multimeter to the battery.

Thoughts so far?

 

I got video, each is about 20MB:

http://mariowc.no-ip.com/charging01.avi

http://mariowc.no-ip.com/charging02.avi

 

P/S I've swapped both alternators and batteries from my beater Prelude, and it has done the same thing.

 

yo I also have a similar prob.

get low volts at the battery,
gauges n stuff fluctuate.

swapped batteries and alts, no help.

but a note for you,
just push down on the throttle while your under the hood, its just like pushing the gas from the cabin, and u can do that while watching the volts(well not easilly.. heh, u'll have to hold both probes on the batt with one hand).

good luck!!

 

Thanks dude, I got my problem fixed. Ended up the alternator plug was dirty and wasn't making good contact.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mario BA4 &raquo;</TD></TR><TR><TD CLASS="quote">Thanks dude, I got my problem fixed. Ended up the alternator plug was dirty and wasn't making good contact. </TD></TR></TABLE>
yo my plug looked kinda dirty too.
was it your green one going into the alt?
or the one that screws on the top of it and has a rubber boot on it?

what did you use to clean it out??

thanks!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tad &raquo;</TD></TR><TR><TD CLASS="quote">
yo my plug looked kinda dirty too.
was it your green one going into the alt?
or the one that screws on the top of it and has a rubber boot on it?

what did you use to clean it out??

thanks!</TD></TR></TABLE>

Yep, it was the green one. I took some contact cleaner and sprayed the plug contacts, and then I took a lil pick and made sure the contacts were looking good. But it did end up killing my alternator as well.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mario BA4 &raquo;</TD></TR><TR><TD CLASS="quote">Yep, it was the green one. I took some contact cleaner and sprayed the plug contacts, and then I took a lil pick and made sure the contacts were looking good. But it did end up killing my alternator as well. </TD></TR></TABLE>

woah, how did your alt die?
from spraying the contact cleaner?
or the bad connection killed it?

 

I am pretty sure that the corrosion and dirt and other junk inside the plug killed the alternator.