98 Civic - Possible electrical problem?

I've had an intriguing issue with my 98 Civic, and thought I might
describe it here, and see if anyone has some insight as to what could
be going on with the car.

Short story: poor fuel economy, alternator test suggests bad
alternator (175 amps?!?!), occasional dimming of lights, otherwise no
problems with the car.

Long story: I've had the car for about 3 years, and it's always been
reliable, except last year when the speedometer started acting crazy,
and the transmission shifted rough. It turned out there was a TSB for
a wire bundle that would run on the intake bracket, causing a fuse to
blow, which caused the other symptoms.

This is the TSB:
http://downloads.hondatech.info/Auto/Service%20Bulletin/x99-029e.pdf

Anyway, I checked that wire bundle and couldn't find anything wrong,
so I just replaced the fuse, and the car was back to normal. Both
before and after this incident, I noticed that the lights (dash,
headlights, dome light) would sometimes flicker or dim, but it was
completely intermittent.

I took the car to AutoZone to get the free battery/alternator test,
and they told me that the alternator was bad, outputting 175 amps! I
don't know if that was the measurement under the tester's load, or
what, but the alternator is only spec'ed at like 80. I thought that
maybe there's a wiring problem that may be causing a load on the
alternator all the time, hurting my fuel economy. (I "only" get 25
miles per gallon)

If anyone has a suggestion, I'd love to try to figure out what's going
on. I'm handy with a multi-meter, I just don't know where to start.
Thanks in advance for any replies.

-Randy

 

Earle,

Thanks for your reply. No, I'm quite certain that none of those items
you mentioned are stuck on. I'm also pretty sure that the "basics" are
good, too, but I'll be sure to double-check.

By the way, I measured 30 volts AC across the battery with the engine
running, and then went and measured another vehicle, and got nearly
the same reading, so I assume that most likely, that's a normal
reading.

I'll be sure to update the thread if I find anything else out.

Thanks again,
Randy

 

Earle,

Thanks for your reply. No, I'm quite certain that none of those items
you mentioned are stuck on. I'm also pretty sure that the "basics" are
good, too, but I'll be sure to double-check.

By the way, I measured 30 volts AC across the battery with the engine
running, and then went and measured another vehicle, and got nearly
the same reading, so I assume that most likely, that's a normal
reading.

I'll be sure to update the thread if I find anything else out.

Thanks again,
Randy

 

I have a '99 HX and it gets 40 mpg, average. It's rated for 45 mpg, but I
live in the mountains. I don't see how a "bad" alternator will output more
than double its rated current for a significant length of time, without
burning up, or what could be loading the alternator enough to hurt mileage.
Your big electrical loads are starter, horn, cooling fan and AC fan. None
of those is stuck on, is it?

In a case like this it is a good idea to go "back to basics" just to make
sure you are not overlooking anything obvious. This would be spark plugs,
ignition wires, cap, rotor, belts and clean battery terminals. Don't
overlook the obvious maintenance items, and it is a whole lot cheaper to
check them yourself. A bad or intermittent connection at the battery post
can have lots of unforeseen results.

Good luck.

Earle

 

I have a '99 HX and it gets 40 mpg, average. It's rated for 45 mpg, but I
live in the mountains. I don't see how a "bad" alternator will output more
than double its rated current for a significant length of time, without
burning up, or what could be loading the alternator enough to hurt mileage.
Your big electrical loads are starter, horn, cooling fan and AC fan. None
of those is stuck on, is it?

In a case like this it is a good idea to go "back to basics" just to make
sure you are not overlooking anything obvious. This would be spark plugs,
ignition wires, cap, rotor, belts and clean battery terminals. Don't
overlook the obvious maintenance items, and it is a whole lot cheaper to
check them yourself. A bad or intermittent connection at the battery post
can have lots of unforeseen results.

Good luck.

Earle

 

The alternator regulator is out not limiting the current. This causes noise
on the voltage leads that the battery cannot filter out. The car is computer
controlled and the noise on the voltage leads cause it to be irratic. this
will cause all sorts of problems as well as poor mileage. Fix the obvious
(alternator) and the rest of your problems should go away. Leave it and it
will destroy the computer and other electrical items in your car.

 

The alternator regulator is out not limiting the current. This causes noise
on the voltage leads that the battery cannot filter out. The car is computer
controlled and the noise on the voltage leads cause it to be irratic. this
will cause all sorts of problems as well as poor mileage. Fix the obvious
(alternator) and the rest of your problems should go away. Leave it and it
will destroy the computer and other electrical items in your car.

 

whoa there. this guy is reading a dc voltage with the meter set on ac.
of course it's way off. don't fix what's not the problem.

 

whoa there. this guy is reading a dc voltage with the meter set on ac.
of course it's way off. don't fix what's not the problem.

 

#1. learn how to use a meter properly. you do /NOT/ measure a dc
voltage with the meter set to ac.
#2. suspect a crock from autozone. there's no way an 80A alternator is
going to output 175A, even intermittently.
#3. check the brushes on the alternator. they're cheap to fix. the
rest of the honda alternator is good for 300k miles very often.
#4. re mileage, check for gotchas like brakes stuck on, dying oxygen
sensors, etc.

 

#1. learn how to use a meter properly. you do /NOT/ measure a dc
voltage with the meter set to ac.
#2. suspect a crock from autozone. there's no way an 80A alternator is
going to output 175A, even intermittently.
#3. check the brushes on the alternator. they're cheap to fix. the
rest of the honda alternator is good for 300k miles very often.
#4. re mileage, check for gotchas like brakes stuck on, dying oxygen
sensors, etc.

 

....

I admit I never thought to measure AC across a vehicle battery. The
alternator is supposed to have diodes in it, which filter out the AC, but I
suppose you are going to get some fluctuation with the alternator making
output. What is the DC voltage?

Earle

 

....

I admit I never thought to measure AC across a vehicle battery. The
alternator is supposed to have diodes in it, which filter out the AC, but I
suppose you are going to get some fluctuation with the alternator making
output. What is the DC voltage?

Earle

 

Does this vehicle have an internal (to the alternator) regulator?

Earle

 

Does this vehicle have an internal (to the alternator) regulator?

Earle

 

You must be using an analog voltmeter, which reads like that on AC ranges.
It just has a series diode to convert AC to half voltage DC, which causes 14
VDC to look like 30 VAC. Reversing the leads will give a voltage of 0, which
also may not be right. Some meters have an "output" jack to let you read
actual AC voltage with superimposed DC voltage. All digital voltmeters work
right.

There should be under 0.1 VAC across the battery with the engine running.
Bad diodes will produce voltages upward of 0.5 VAC; the last one I saw read
1.7 VAC.

Mike

 

You must be using an analog voltmeter, which reads like that on AC ranges.
It just has a series diode to convert AC to half voltage DC, which causes 14
VDC to look like 30 VAC. Reversing the leads will give a voltage of 0, which
also may not be right. Some meters have an "output" jack to let you read
actual AC voltage with superimposed DC voltage. All digital voltmeters work
right.

There should be under 0.1 VAC across the battery with the engine running.
Bad diodes will produce voltages upward of 0.5 VAC; the last one I saw read
1.7 VAC.

Mike

 

You must be using an analog voltmeter, which reads like that on AC ranges.

Nope, it's a digital multimeter, but admittedly a dirt-cheap (sub-$10)
one. Still, I guess I should have realized that it was probably just
doubling whatever voltage it saw, hence that reading.

More in a reply to "jim beam" later in this thread.

Thanks again for your time and response!

-Randy

 

You must be using an analog voltmeter, which reads like that on AC ranges.

Nope, it's a digital multimeter, but admittedly a dirt-cheap (sub-$10)
one. Still, I guess I should have realized that it was probably just
doubling whatever voltage it saw, hence that reading.

More in a reply to "jim beam" later in this thread.

Thanks again for your time and response!

-Randy

 

#1. learn how to use a meter properly. you do /NOT/ measure a dc

Before I go any further, I want you know that I'm grateful for your
help. That said... I'm pretty sure I know how to use a multimeter. My
intention was NOT to learn the DC voltage, but rather the amount of AC
ripple, which exists in any DC generated by a rectifying circuit.
Obviously, since I measured pretty much the same thing on another
"good" vehicle, either my meter was wrong, or I'm not using it right,
but I'm going to blame the sub-$10 digital multimeter, unless you tell
me there's a different way to measure AC ripple on a DC voltage.

I'm leery of what they told me, but I'm confused as to how two
different stores, 6 months apart, managed to measure the same thing,
and make the same diagnosis. I'd believe you over them any day, but
I'm still curious as to what they're measuring...

This is great advice. I never even considered the brakes/O2 sensors,
either of which could be faulty by 150k miles, and would definitely
impact fuel economy. Hmmm, O2 sensors... Maybe that cheap-***
multimeter will come in handy, after all! At least I know how to get
DC voltage readings from it, for sure!

Thank you again for your time and help.

-Randy