[JeffreyO]

RPM Dependant Electronics Issues?

So, let's hear your ideas. This one has me baffled.

I'm driving down the road, enjoying some sunshine in Seattle, when suddenly my battery light comes on. I ponder to myself what the issue is, my first thought was alternator was going out. I was crusing between 2000-2500 rpm's. Suddnely, the radio minus the subs goes quiet, the deck is still working, I am not far from home, so I decide to haul ass, and turn around, and get home before the battery is drained. When I get to a stop, suddenly, the check battery light goes off, and the radio turns back on fullblast. Now this should be opposite of what should happen. Normally it chargse more when driving. So I open the console and check the turbo timer. Lo' and behold I'm getting 14.* voltage. At worst, it drops to 13.8 when I let off the gas, and brings itself back to 14. When I hit the gas, and I tested several times, it'll max out at 18 depending on how hard I hit it, and then drop back down to 14. If I hold high enough revs for awhile, my ABS light comes on. The battery light stays off until I reach about 1900 RPM's. Beyond that it stays on and 3 seconds after it comes on, the radio shuts off all speakers except the subs.

Knowing that the bettery is getting a proper charge, and I still have full voltage, what do you guys think? Short somewhere? Isn't it odd though that the problems are RPM dependant? I'm open to any ideas.

 

[Kurdain]

Well.
A normal car normally charges around 14 volts if I recall correctly.
Seeing that your voltage is RPM dependant I would say your voltage regulator is starting to go out, however I am not sure if they are built into the alternator on the MR2 or if its external (most are in the internal to the alternator if I recall correctly).

I am not sure how to check this, possibly turn off everything possible that's electrical and check the voltage at different RPM's as close to the alternator as possible and at the battery terminals.

COULD have a bad cell in your battery too maybe....long shot. How old is your battery? Does it seem strong? Might be putting a large load on your alternator and causing it to freak out.

As far as thing shutting down of going goofy it might be your amps protection circuit kicking in from either an under or over voltage situation, that's why your deck was still on. Also I guess your relays and sensors could freak out too explaining the dash lights and stuff.

Dunno if I helped or not....

 

[JeffreyO]

Somewhat. The battery is getting a good charge and is showing a good charge when the car is off, so it's not the battery. Voltage regulator you say? Might be. I really don't want to drive it much until i find out the issue. I don't know what other electronics will turn off . Is it possible it's a short somewhere? I still don't get why it's rpm dependant... and it's not overcharging. It stops at 18. Although voltage regulator sounds like the right path. I 'd hate to get a new alt to find out that's not the issue though.

 

[Kurdain]

Well,
Old generators before they came out with alternators would charge more and more the faster you spun them, i.e. higher rpms.
So at an idle your lights and everythign would dim and flicker, pretty annoying. (old cob-webs memory kicking in here...) Alternators pretty much relieved that as they use a slight charge from the battery at low rpm's to generate a constant voltage and current. I do not think you should be going to 18 volts, should stay around 14.
However I am pulling this from old school muscle car memory so hopefully someone will chime in.

It could be a bad ground, electrical can be such a pain in the butt as 1 small problem can appear in several places and make you chase your tail for hours....

Otherwise you can try replacing the alternator or take it to a shop, but either way you are going to be out cash.
If you were REALLY careful and didn't get the alternator dirty you could install it, try it, and take it back if it didn't fix it. But my engine bay is a mess under the engine so good luck there heh.

Hopefully someone will chime in that has more specific MR2 experience.