Flashy Battery and heater lights on dash

I got two lights that keep flickering at low rpms and go off at higher
rpms (2500 or so)
was intermittent now is doing it most of the time, the lights stay on
below 2000 and flicker up to 2500 or so then go off after that
its the battery light and the light that looks like a radiator or
catylitic converter with heat wiggles above.
85 honda integra, 1600 dohc injected 5 spd.

 

It sure sounds like a bad alternator to me. Getting the alternator out
probably takes an act of God, so you want to diagnose it first if possible.

If you have access to a digital voltmeter, measure the AC voltage across the
battery with the engine running. It should be below 0.1 VAC, usually below
0.05 VAC. Readings of 0.5 VAC or more are a strong indication of a bad diode
(or several) in the alternator. That would be consistent with the flickering
battery light.

Mike

 

Sometimes car makers do funny things like tying warning lamps together
with diodes in order to implement lamp test. My guess is that your
coolant temperature alarm is tied to the alternator warning light so
that if the latter comes on, the former comes on too (but not vice
versa). This is done so that you have a chance to check that the
temperature warning light bulb is good. So, my guess is that there is no
problem with the cooling system.

Alternator light flickering or staying on at low RPM is a typical
symptom of a bad alternator. It could be a case of bad diodes as
"Michael Pardee" suggested and his test is easy enough to do. I if the
alternator is original to the car it is more likely to be worn out
brushes. They are replaceable, but I don't know how easy it is to get
access with the alternator still in the car. The nominal output voltage
from the alternator is 14.5 V for every Honda I have checked (back to
1987), your Integra is probably the same. Start the engine and turn on
your headlights. Then measure the voltage at the battery. Slowly
increase the RPM to about 3000. As you raise the RPM, the voltage should
stabilize at 14.5 V +/- 0.6 V. With a good alternator the voltage should
stabilize at 14.5V +/- 0.6 V at or just above idle. In your case the
voltage probably reaches 14.5 V at around 2000 - 2500 RPM. If so,
alternator is bad.

A bad battery can also make the alternator light come on. Also, a bad
battery will wear out your alternator quickly. If your battery is more
than 4 years old, I would replace it just as a matter of course. It can
sometimes be hard to find out if the battery or the alternator is at
fault; A bad battery can be a huge load and drag down the voltage from
the alternator, particularly at low RPM. Conversely, a failing
alternator will not charge the battery properly, reducing the voltage.
If you measure the battery voltage before starting the car (after it has
not been used for at least several hours) you should see at least 12.6
V, If you do, then the battery is not causing your alternator light to
come on. If you see less than 10.5V, then the battery is most likely
bad. Inbetween? most likely a problem with the alternator.

 

Ok done the check, 1200rpm the voltage across the battery is 15V. I put
the setting on 200 ACV and the readout at 1200rpm was 30.0? is that
right? or was i supposed to do something else?

 

Caleb wrote:

15V is a bit high, but within spec. (In my experience, even though the
spec is +/- 0.6V, the voltage is usually well within +/- 0.1V) With the
instrument on DCV, what voltage do you measure at idle, at 1200 RPM, at
2400 RPM and at 3600 RPM?

The reading of 30.0 on ACV is bizarre. Different meters behave
differently on the AC setting (i.e. a precious few measure the true RMS
voltage of the signal, most measure the RMS value of the AC component
only), but regardless, 30.0 V is very high. Could it be that it was 30.0
mV? What type of instrument do you have?

With the instrument set to DCV, what voltage do you read with the
ignition off?

 

Oops... it sounds like your meter is like most analog meters - it just uses
a rectifier with no blocking capacitor to measure AC. Those don't work for
this test because of the DC voltage riding on the battery. Try another
digital voltmeter if you can get your hands on one.

Mike