Celica -76, 18RC poor voltage regulation.

[Paxman]

Hi!

My first thread here and I'm hoping to get some advice on the charging in my car. I have had some problems with the car stalling when idling so I have troubleshooted the charging and found that the voltage was really low. The alternator was checked by a professional alternator/starter shop and the regulator is new. The new regulator bumped up the voltage but the voltage is still really variable.

The following is what I have found using a multimeter connected to my cigarett lighter outlet.

At idle revs:

No electrical load= around 14 volts
Normal load i.e. headlights and cabin fan on setting 1= around 12 volts and slowly decreasing.

At normal speed revs:

No load= over 15 volts.
Normal load (see above)= around 14,4 volts.

I did see voltage over 17 volts the other day so I checked all the wires. I found some weird connections which I fixed and now the voltage is what I wrote above.

What is normal variations in the voltage in these cars? I don't really like the values over 15 volts and below 12 volts and I thought the new regulator would regulate better than this. Can it be the alternator even if it tested fine?

Best regards
Fred

[ta22fan]

Anything around 12.5 to 14.5 volts is reasonable depending on temperature and load, so these numbers don't sound too bad. What makes you think this is an electrical issue? If stalling at idle is your only symptom, I'd start with fuel and vacuum. Are you running the stock carby? Couple of pretty simple things that it could be in that case. Check your vacuum (mainly hoses) for any leaks - poor idle is a classic symptom of a vacuum leak somewhere.

[Paxman]

Thank's for your reply ta22fan,

I'm 100 % sure the stalling was due to bad charging. I saw the lights dim before it happened so I set up the multimeter with a cigarett plug and got it confirmed, voltage dropped way under 12 volts. This also only happened when the retro fitted electric cooling fan started when sitting in traffic on a hot day.

I know that 12.5 to 14.5 is OK but since my voltage is so connected to the load and the revs I still think something is wrong. And I should never see over 15 volts for prolonged time since that can damage the battery and other electrical components.

Also, I have tested three different batteries, two of which I know are good.

[ta22fan]

Charging voltage of 15 and even a bit more are reasonably normal for short periods, but you are right - you should not see anything that high for extended periods. Check your earth/ground. Sounds like you've got a new voltage regulator installed - double check that you have the correct unit and that it is wired in right. Older engines are surprisingly tolerant to low/variable voltage on the primary ignitiion circuit (assuming the coil & points are in Ok condition) once running and warm - you'll still get enough spark to maintain idle at 9 volts or even less - which is what makes me suspect it could be something else.

[ctrain]

Do a voltage drop test between your battery and the positive (B+) on the alternator, there shouldn't be anymore then .5v of resistance, also do it across all your connections from the battery to the alternator, its a simple test that can rule out anything. You shouldn't see anymore then .2v over a connection and .5v over a circuit.

EDIT: I just read that you check all the wires, i should of read that before posting, also try not using the cigarette lighter outlet as your test point, actually connect the multimeter to the alternator just to be sure.

Cheers,
Callum

[Paxman]

Charging voltage of 15 and even a bit more are reasonably normal for short periods, but you are right - you should not see anything that high for extended periods. Check your earth/ground. Sounds like you've got a new voltage regulator installed - double check that you have the correct unit and that it is wired in right. Older engines are surprisingly tolerant to low/variable voltage on the primary ignitiion circuit (assuming the coil & points are in Ok condition) once running and warm - you'll still get enough spark to maintain idle at 9 volts or even less - which is what makes me suspect it could be something else.

Yes, I have a new regulator installed. It not an original but it looks basically the same, has the same connector and even wires with correct colors. I got it from a generator shop that tested the alternator. The new regulator bumped the voltage so it's better than the old one.

Forget about the stalling. Since I found that it was due to low voltage it has never happened again, I just turned off the headlights when I saw that the fan started and I got a new battery...not a repair but a temporary fix. Now I'm after a permanent fix and that's why I'm doing this troubleshooting and writing on forums about the strange voltage regulator.

Lets say the regulator is fine, the wires are correct and the battery is good. Can the alternator be bad even though it tested good at the shop? Can a bad alternator in a otherwise good system give the symptoms I have?

[Paxman]

Do a voltage drop test between your battery and the positive (B+) on the alternator, there shouldn't be anymore then .5v of resistance, also do it across all your connections from the battery to the alternator, its a simple test that can rule out anything. You shouldn't see anymore then .2v over a connection and .5v over a circuit.

EDIT: I just read that you check all the wires, i should of read that before posting, also try not using the cigarette lighter outlet as your test point, actually connect the multimeter to the alternator just to be sure.

Cheers,
Callum

I'd love to do a voltage drop test but the voltage varies so much it'll be impossible. I'll try connecting to the alternator instead and see if that will give a more stable reading. I don't think that the readings that are too high are due to the cigarett lighter outlet though...

I'm doing a schematic based on the original schematics that will show exactly how my car is wired, even where everything is located in the car. I did quite big changes to the layout when I restored the car which I'm starting to regret now...but I was young and ambitious and not really thinking of the consequences...:-/ Will post the schematic when I have something to show!

[ta22fan]

Lets say the regulator is fine, the wires are correct and the battery is good. Can the alternator be bad even though it tested good at the shop? Can a bad alternator in a otherwise good system give the symptoms I have?

Getting beyond my experience Fred. If the shop knew what they were about, a tested unit should be 100% good. These are pretty simple devices that with the right test gear will give a pretty clear "good/bad" test result. I've only ever seen low voltage as a fault symptom, but I believe that high voltage is possible in rare circumstances. Maybe a bit drastic, but if you are pretty certain the alternator is the problem - maybe swap it out and see.

[Paxman]

Actually, the low voltage at idle is not my main concern. I can live with a low voltage at low revs since this is an old car and the 50 amps alternator is the original one. It was never meant to serve a heavy cooling fan at idle rpms with head lights and break lights on. My main concern is the fluctuating voltage and that there seems to be little or no regulation.

[Paxman]

Today I did some changes in the wiring, see this thread, which got my ammeter to work as it should. Problem is that now the voltage varies even more! Now it even effects the lights to the extent that they are visibly dimming intermittently. The multimeter shows violent fluctuations in the voltage that correspond to the dimming of the lights...

I'm going crazy here...

[Paxman]

This is the schematic that I'm working on. It will show the components that are in my car and roughly where they are placed in the car. The part here is the charging part. Does anything stand out that can be the culprit?

[ta22fan]

No help here - sorry. In your shoes I think I'd be off to an auto-electrician at this point.

[ctrain]

If you can be bothered to make a video it would help alot, it does seem like the regulator is not working as it should, are you using the original external voltage regulator mounted in the engine bay or is it in/on the alternator?

[Paxman]

ctrain,

I'll see what I can do about a video. The alternator is the original one and was tested fine, the voltage regulator is new but old style external one and should be functional unless I have messed it up somehow. I have no fusible link but instead I have the 16 AWG wire to make the ammeter work (see the thread I linked too above).

The weirdest thing is that sometimes the voltage is rock solid at a little over 14 volts where it should be...then suddenly it starts to freak out. It's really hard to diagnose since I can't really find a pattern. I'v been away for a few days so I haven't tested more but will do more now. I have also bought a length of white wire to replace the one in the car. After that is done there isn't much more to swap out except the alternator...

[Paxman]

Just a quick update (borderline dubble post with the ammeter thread but I hope no one minds):

I'm getting cautiously optimistic here!

Today I installed all new white cables to a terminal block for common hot feed. With some hesitation I turned the main switch listening after the snap sound of a fuse or wire burning off and sniffing after the characteristic odor of really hot wire insulation but nothing indicated that there was anything wrong. I did hear the clock start ticking and I tested the headlights and other users, all seemed good. Holding my breath I turned the ignition key...the car started as is should and nothing bad appeared to happen! I hooked up the multimeter to check the voltage and lore and behold the charging seems to work now!! 😄 I need to take the car out on the road to see if the this issue really is solved so I have some interior trim reinstalling to do but I haven't seen voltage values this good before!

To be continued...