weatherman

About 6 months ago I sporadically ran into a problem of my aftermarket Alpine not coming on, or cutting out at high volume. This has slowly become more frequent. Sometimes a few of the backlit buttons flash regularly but sometimes the display goes completely.

It's a 4x60W head unit so runs a direct positive lead to the battery.

I think that for whatever reason the unit is not getting sufficient voltage.

There's been no problem starting the car.

Interestingly today after about 20 minutes into a motorway journey the radio again cut out. I noticed that the voltage as measured by a car thermometer attached to the cigarette lighter socket was sitting at around 12.5V (normally 14.5V while the car is running).

The most interesting part was, that when I had to brake for some roadworks, the radio suddenly came on and I noticed the voltage had jumped back up to 14V. Then once I finished braking the voltage fell back and the radio went off.

I wondered if it was the fact that the brake lights were on that caused the alternator to start charging the battery again (I believe that this doesn't happen while the car is warming up unless a power source is used) so I put on the sidelights and the voltage came back up and the radio came on! After about another 30 minutes I put the sidelights off and the voltage stayed up for the rest of the journey and the radio stayed on.

So I'm slightly confused - obviously I will get a battery check done but wondered if the symptoms themselves pointed one way or another.

I have thought that I've heard a ticking noise while coasting up to the lights but it disappears when I come to a stop and can't replicate the sound by revving the engine at a standstill.

Looking at the following webpage http://www.international-auto.com/fi...-voltmeter.cfm the only slight variance is that on occasion when the car is off the battery shows just under 12V (triggering an alarm from the voltage meter) so perhaps the radio problem is an early sign that the battery is not holding a full charge (it really needs to be 80-90% to show more than 14V) and because the radio is taking the power direct from the battery rather than through the general electrics it's running into problems first. And if the alternator charging is not occurring at the start of a journey due to no lights being on, then the radio only kicks into life once the alternator is forced to start charging the battery.

Anyway, I think I have convinced myself slightly it's the battery, but do any electrical gurus on here agree or disagree?

Stuart

albob

(not a Guru!)
reading your post, at the beginning i thought - "loose wire/connection" : but, the last section of your post makes a lot of sense

radio drains battery, until voltage to low to run radio

(battery a lot cheaper than alternator !!)

Have u tried 'thumping' the area around the radio, to see if it cuts out?

alan

alcazar

iTrader: (2)

OK, first things first.

Look for the cheap option. So......check ALL connections. Remake any dodgy looking ones, always soldering if you can. That INCLUDES the earth connection, of course.

Then check the tightness of BOTH battery connections, and any earth wires leading to the battery at BOTH ends. Look for corrosion etc.

IF the problem persists, then get your battery checked out. And NOT by QuikFit or the like. Use a proper auto electrician.

If the battery checks out OK, then suspect the alternator.

Dutch Scooby lover

iTrader: (3)

I would think alternator at this time.
Getting a 12v current on the lighter socket is on the very low side.

Have you tried using the rear defrost, as that extra load should certainly get the alternator to actually turn on (the alternator spins with the engine all the time, but only at certain conditions the ECU sends out a signal to the alternator to actually start charging, the defrost should be one of them)

Can you check on the battery terminals with the defrost on, as the lighter socket could give a different reading (wire length/damage etc).You should see 13.5/14 volts between the positive and negative terminal that way.

Don Clark

Nothing to do with the ECU at all (total myth).

The alternator has its own voltage regulator..........

https://www.scoobynet.com/showpost.p...9&postcount=29

https://www.scoobynet.com/showpost.p...2&postcount=31



To answer the OP, your problem could be either or both......
Battery on its last legs
Alternator with a suspect voltage regulator

Dutch Scooby lover

iTrader: (3)

Then why does my MY98 have a 3 wire plug, and my Syvecs ECU has a Alternator output??

When I removed my gauge binnacle, to replace it with a Stack the alternator left me stranded with a flat battery.The charging light is connected to the alternator, but why is there a wire going from the alternator circuit to/from the ECU, besides the charge light wire??

Don Clark

I think Syvecs ECU says it all.

Power supply routing for OEM LHD 98 Impreza......



Charging circuit for same..........



Strandard 97/98 ECU pin outs.......

Don Clark

Hmmm, don't see any Alternator specific output here...........
I see a couple of Ignition controlled inputs.........

http://www.syvecs.com/forum/viewtopi...7&start=0#p840

Dutch Scooby lover

iTrader: (3)

You can assign a output for the alternator in de SCal software.
(on/off rpm, combined with on/off voltage)

There are surplus outputs, as the My98 uses a different idle control valve then the later classics.

Also, the list only has 55 pins covered, and the plugs contain 64 terminals.

If you take the back of the MY98 cluster (the plastic circuit board, and trace the wiring to the charge light on the stock cluster you'll see 3 wires, the third goes to a undescribed pin on one of the plugs.
(Changed the cluster 3 years ago, so not sure of which terminal, but there is a wire going from the alternator charge light circuit in the cluster to the ECU.

(It could be that is has nothing to do with the alternator, but why put it there)
If the alternator has it's own brain/logic about charging/not charging, why run a wire to the ECU??

Don Clark

The standard OEM setup doesn't require an output from the ECU as it has its own voltage regulator and monitors the load from the ignition side of the things.

As the alternator link is not listed in the Syvecs pin out pages, it would suggest it's not required for an Impreza and maybe that is what's causing your battery to discharge as it would be on load all the time.

If you were running a competition alternator it may be that the ECU output can be used as the load signal to the alternator, rather than the ignition/acc circuits.

weatherman

Thanks for replies. Radio won't come on at all now, doesn't even flash, voltage while running is just over 14V and when I stop drops to 13V, perhaps 11.8V when starting up the next day.

Might be the radio itself, I'll connect another battery in parallel as if I'm jump starting, and if it still doesn't come on it must be the radio.

It's previously been my experience that if a battery is low on juice, being able to start the car becomes impossible well before any radios give up the ghost!

Stuart

alcazar

iTrader: (2)

Is there a small fuse either inline to the radio, or on it's rear, under a cover etc?

Worth checking.

weatherman

Just connected in parallel with another car and still the radio won't come on. So I don't think it is anything to do with the alternator or battery, which is something!

I see a 20A fuse on the red lead near the battery, will check it though would have thought that if it was the issue, I wouldn't have had a long period of intermittent failures, unless there is shorting somewhere which has finally melted the fuse!

Stuart

alcazar

iTrader: (2)

Ah......the intermittent is a pain.

That could be a duff headunit.........

Don Clark

Update.....

Following a post by Rob84 elsewhere, have had another look and it appears that with the introduction of CANBus (Hawkeye onwards??) some models are fitted with Alternators that have 4 wire connections not 3.

The additional connection goes to the ECU (ALT-1)