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
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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

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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
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...

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
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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.

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Woody wrote:

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.

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

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his meter could measure pulsating DC on the AC mode,especially if it's a True RMS meter. 30VAC seems odd.
DCV is more important,though.
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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
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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
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That's good to know. I have a couple of really cheap DVMs to carry in the cars and they may do the same. I ought to check. Thanks!
Mike
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snipped-for-privacy@gmail.com wrote:

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.
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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
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With regards to your crazy speedo, I had the same problem recently on my 98 Civic LX. Here are pics of what I found was wrong. The short blew my #15 fuse, which is for the Alternator and BOTH O2 sensors. If you've been driving around with this fuse blown, it would make sense that your mileage is in the pooper.
My car runs like a top now, mileage back to high 30s. (and it has almost 300k kms on it)
Pics have been uploaded to
http://www.tegger.com/hondafaq/misc/96-99_civic_mil%26fuse15 /
t
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If fuse 15 blew, CEL is on. If its not, its probably burnt out. It has to go on as this is the fuse for the alternator and the O2 sensors. no power to O2 sensors = P0135 and P0141.
t
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Me, too. Overcurrent should be nearly impossible, because of the physics of the windings. http://tegger.com/hondafaq/altcharge.html Maybe the regulator is running wide open? I'm grasping at straws here.
I'm sure your situation is frustrating, but you're providing some interesting glimpses into the "shouldn't work that way" areas :-} As Mr. Spock would observe in the old Star Trek series, "Fascinating."
Mike
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snipped-for-privacy@gmail.com wrote:

i doubt a meter that cheap will give you ripple since it'll need to "offset" the dc. also, the ripple should be something of a funky waveform since the alternator is 3-phase - it'll be 3 full-wave rectified bumps, superimposed at 120 degrees each - so a cheapo r.m.s. approximation will be off too. if you have one rectifier out, waveform will be real ugly - ugly enough to cause noise on the audio system. borrow an oscilloscope if you want to get serious about that stuff.
in the mean time, measure the dc voltage at idle, no load and at idle, full load. if the readings are within spec, it's probably just brushes giving you that startup flicker. also, check the gotcha of belt tightness.

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jim beam wrote:
<snip>

Plenty of cheap meters (including my $7.99 no-name digital DMM) will read the ripple on top of a DC voltage. On the AC setting, the input signal is AC coupled (through a capacitor).
Regardless, both the poster's car and a known good car measure 30V ripple. This simply isn't so. There is something wrong with the meter or the method.
<snip>

With the caveat that on some cars (like my '94 Civic) the set point for the voltage regulator is lowered while at idle (if a few other conditions are met). Bumping the RPMs up a tad from Idle makes the set point return to 14.5V (nominal).
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The fuse has reblown....
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