98 Civic - Possible electrical problem?

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

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.

#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

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

Mike

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

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

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

Pics have been uploaded to

snipped-for-privacy@gmail.com wrote:

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

Me, too. Overcurrent should be nearly impossible, because of the physics of the windings.

Mike

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.

"Earle Horton" wrote in news:BNydnfMdVZVIipbbnZ2dnUVZ snipped-for-privacy@comcast.com:

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.

"loewent via CarKB.com" wrote in news:6fe61a42fbc3e@uwe:

Wouldn't that turn on the CEL and set a code or two?

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.

Jim Yanik wrote:

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.

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).