98 Civic - Possible electrical problem?

#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

 

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

 

The fuse has reblown....

 

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

 

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. 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

 

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

 

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.

 

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.

 

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.

 

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.

 

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.

t

 

jim beam 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).

 

jim beam 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).