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Electrical problem - sounds like the alternator?

dmention7

dmention7

Hater
Long story short, I'm driving a 2002 civic for awhile so I can do some work on the MSP.

Yesterday while driving home from work, after about 25-30 miles on the freeway, the radio started cutting out, then the ABS light came on, and then a minute later the instrument cluster went dead. I turned off the headlights, and things powered back up and were fine for the rest of the way home. It started nice and strong this morning.

This morning while driving though, the same thing happened about 25-30 miles out except the cluster stayed dead. I kept on driving and about 5 miles later the car started to lose power (probably low spark) so I started to pull over on the shoulder. Well, as soon as I got down to about 55mph, the gauge cluster spring back to life. I stopped and let it idle for a minute, then took off again. As soon as I passed 60mph the gauges died, so I exited the freeway and took highways the rest of the way to work and kept it under 60.

The only explanation I can think of is that the alternator loses its ability to charge above a certain engine speed and after about 30 minutes on the freeway, I've drained the battery. But the 10 minutes or so of slow driving I do before reaching my destination is enough to juice the battery back up enough to start. I've just never heard of an alternator acting like that.... anything else I should look into?
 
mndsm

mndsm

I'M OFFENDED!
Sounds like an alternator to me. The only other thing I can think of is something within the intsrument cluster is requiring x draw above whatever RPM 60mph= in a Civic, and it's eating it. Not as likely I'd guess, but possible. If the alternator is anything like a normal electric motor, whats probably happening is that it's not able to make solid whatever contact it needs to make electricity above that RPM.

Plus it's a Honda.
 
dmention7

dmention7

Hater
Any thoughts on why the alternator would start to crap out at higher rpms though? That just seems kind of strange to me.

Maybe the belt is so loose that it's not even squealing or something...
 
mndsm

mndsm

I'M OFFENDED!
Maybe it slips at higher RPMS and it just isn't spinning anymore, or like I said, maybe the core is so shot it can't make good contact to generate the electricities.
 
D

DrWebster

Guest
While I tend to agree that it's something alternator-related, I wouldn't discount the possibility of a dirty ground somewhere. I had the ground wire to my sub come loose once in my old car, and it did some wack shit -- not just to the sub, but the whole car.

Here's another thing to take into account: Alternators are driven before the transmission, not after. Vehicle speed doesn't matter so much as engine RPM. Try screaming along in 2nd at like 4k RPM and see if the problem happens then.
 
dmention7

dmention7

Hater
It's definitely engine speed related. The magic number turned out to be right around 2500rpms or 60mph in overdrive. Funny thing is when the cluster would die, if I took my foot off the gas and put it in neutral, it would spark back up again almost instantly.

Incidentally I thought I might have solved it when I left work because the positive battery cable was pretty loose on the battery post. So I jammed some scrap copper foil in there to make a tighter connection, but no dice. I'll have to dig around the wiring a bit more when I get back on monday to see if there is a loose connection before I drop $140 on a new alternator.

Looks like I might be back to driving the MSP on shot wheel bearings for a couple few more days. lol
 
Big Nate

Big Nate

Chaos Engineer
Jay, you have done a lot of electrical work on your car and changed a lot of stuff around. I would take some time with a Multimeter and test everything you have. You can also test your own alternator. See this thread. That will get you started. If you need help I can see if I can free up some time.
 
dmention7

dmention7

Hater
So, here are some results of poking around with a multimeter:

Battery voltage: 12.2v (plenty of juice in there)

Alternator to ground with car off: 12.2v
Alternator voltage at idle: 14.5v (right where it should be)
Alternator voltage at idle with headlights, fan, defroster, radio, interior lights all on: 12.3v or so.
Rev the motor to 2000rpms: 12.5v
Rev the motor to 3000 rpsm: 11.5v

So, right off the bat, the alternator is barely able to keep up with the accessory load at idle. Speeding up the motor helps, but then past that 2500 rpms, the alternator falls on its face. Kinda weird... but does anyone know anything else I should check before I order a new alternator?

Oh, and thanks for the help!
 
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