Alternator or other issue?

[Twisties]

Hey Guys,

I have just bought a 92 GTS with what looks like an alternator issue

It runs and drives for about 5 minutes before the battery goes flat.

Batter reads over 12v when the engine is off and -12v when the engie is running. The alternator has been replaced but the problem remains. I bought the car with the new alternator fitted and the problem described so i cant tell if the symptoms have changed since the original alternator was removed.

I have been told there are various alternators for the mr2 and that it could have the wrong one fitted now.

Any other ideas before i try to change it again?

Also there is a drain of about 10a with the ignition on but the car not running. I tested this by removing the earth lead off the battery, turning the ignition on and reading with a meter. Does this sound ok?

[GDII]

-12V when running sounds wrong and 10Amps draw when off is huge if that is reading correctly.

With the car off the battery should read ~12V.
With the car running the battery should read 14.7V if everything is healthy.
If it reads less than 12V then there is something wrong.
You should only be getting milliamps (mA) draw on the battery when the car is off. But it all depends on what other items are connected to the car. Alarms, stereos or other aftermarket accessories.

[Twisties]

There were probably a few things running but like you say sounds quite a lot. Weird that the battery reads negative when running though. Is that a bad alternator or the wrong alternator. Indisconnected the alrernator and the draw dropped a few amps

[GDII]

What pins are you using to connect the leads on the multimeter to when the car is running? And what settings are you using?

[Twisties]

Im just reading the voltage directly off the battery. The battery is new and freshly charged.

Meter is set to DC20V

Ignition off 12.7v positive. So normal
Car running -12v negative. Not the 14v you would see on a working alternator.

Is that how it would look if the alternator wasnt charging? Its my assumption but the alternator was just replaced and did not fix the problem. Is it a second bad alternator or is there anything else that could cause it?

Ive removed trim and looked for bare wiring etc.
Some of the ECU wiring is rough or snipped. I am working out what each one does at the moment. Aftermarket Mines ECU

[GDII]

If the battery is reading 12.7V with the car off it should read ~11V but no lower than 7V when the car is running. The ECU would most likely cutout with anything lower than 7V.

The multimeter should have the black lead in COMM socket and the red lead in V/mA socket. Not the 10A socket.

The ECU doesn't control the charging system, it's completely separate. The MINES ECU will be a direct plugin so the stock wiring diagram/ECU can give you most of the answers. The stock ECU has the codes written on the board inside the case. Not sure about the MINES unit.

Download the 1993 diagram from here http://mr2.org.nz/phpbb3/viewtopic.php? ... 49#p125056 and cross check colours and pin outs. Keep in mind this is the USDM diagram, the JDM cars are slightly different but most is correct. If you use the diagram and look at the car it's easier to figure out.
Page 56 has the charging system which only really consists of 4 wires/circuits. Charing issues can be hard to pin point but the battery can be the problem too. Hopefully not the problem with yours.

Things to check

Main wire (White) direct to battery. This has a 120A fuse in the front of the car that if you ground the white wire on the car body with the battery connected it will blow. First hand experience.
7.5A ALT Sensing Fuse
7.5A ECU-IG fuse. If this was blown the car wouldn't run though.
Charge light in the dashboard. Some cars won't charge if this bulb is out. Not sure if this is true in the MR2.
Voltage regulators car go bad. Yes it's new but new parts can be faulty.
The rectifier can go bad even in a new alternator. Had one die on me 4 weeks after purchase.
Brushes and slip rings.
The last three things are normally associated with old alternators.

Does the CAT temp sensor light and the Intercooler fan light come on when the car runs? The NA cars also have a volt meter where the boost gauge is and this can assist in telling you if it is charging. This is no help to you but for others with NA cars who might read this.

[Twisties]

Thanks for that. You’ve given me a few things to check tomorrow. Will let you know how I go

[Twisties]

Getting more reasonable figures today.

12.3v ignitionoff
11.5v running
0.22a draw ignition off
10a draw with ignition on. Same with alternator disconnected. A mechanic advised me to do that test. I guess to see if the alternator is shorting.

Is 10a ok with the ignition on?

[GDII]

That's a bit more like what I was expecting from an alternator that isn't working on a new battery.

I'm not sure if 10A with ignition on is normal or not. Others might be able to advise.

Have you checked the wiring for continuity? If this car has been messed with then the wiring could be broken or wired incorrectly. Hard to tell without seeing the car.

[Twisties]

I checked the fuse.
This battery light comes on and off as normal.
I am feeling like it is just going to need a new alternator.

Is it true that there are different versions and some might not work with other models?

[GDII]

It could be the alternator. Take it in to get tested first before paying lots for another. Then you can eliminate the alternator as an issue.

Yes it is true there are different types of alternators for the SW20.
They are different AMP ratings for different cars. Some didn't have powersteering so have lower AMP ratings.
The newer cars from 1993/08 have a different mounts.
The older alternators have a round plug for the 3 wires and the newer ones have an oval plug.

There are 7 different alternators for the SW20 from Japan. Some are 80A, 90A, and 100A. I have one from an ST182 Celica. It works but the pulley has an extra tooth so the belt sits to one side but works fine.

[Twisties]

awesome advice as always. This one has power steering so i will look out for one with the higher rating.

I wonder if the one fitted is 80a and whether that would be why its not supplying enough power

[Ballist1x]

If the battery is reading 12.7V with the car off it should read ~11V but no lower than 7V when the car is running. The ECU would most likely cutout with anything lower than 7V.

The multimeter should have the black lead in COMM socket and the red lead in V/mA socket. Not the 10A socket.

The ECU doesn't control the charging system, it's completely separate. The MINES ECU will be a direct plugin so the stock wiring diagram/ECU can give you most of the answers. The stock ECU has the codes written on the board inside the case. Not sure about the MINES unit.

Download the 1993 diagram from here http://mr2.org.nz/phpbb3/viewtopic.php? ... 49#p125056 and cross check colours and pin outs. Keep in mind this is the USDM diagram, the JDM cars are slightly different but most is correct. If you use the diagram and look at the car it's easier to figure out.
Page 56 has the charging system which only really consists of 4 wires/circuits. Charing issues can be hard to pin point but the battery can be the problem too. Hopefully not the problem with yours.

Things to check

Main wire (White) direct to battery. This has a 120A fuse in the front of the car that if you ground the white wire on the car body with the battery connected it will blow. First hand experience.
7.5A ALT Sensing Fuse
7.5A ECU-IG fuse. If this was blown the car wouldn't run though.
Charge light in the dashboard. Some cars won't charge if this bulb is out. Not sure if this is true in the MR2.
Voltage regulators car go bad. Yes it's new but new parts can be faulty.
The rectifier can go bad even in a new alternator. Had one die on me 4 weeks after purchase.
Brushes and slip rings.
The last three things are normally associated with old alternators.

Does the CAT temp sensor light and the Intercooler fan light come on when the car runs? The NA cars also have a volt meter where the boost gauge is and this can assist in telling you if it is charging. This is no help to you but for others with NA cars who might read this.

Hi really old thread bump, but my cat light and the temp sensor light came on at the same time and tonight my car nearly stalled when I was parking up and I noticed my speedo flickering when I used my indicator amd my speakers turned off by themselves...

What does the rwo lights on mean? My cat was deleted and cold and my temp fan runs no problem so not sure why they are on.

[GDII]

If the battery is reading 12.7V with the car off it should read ~11V but no lower than 7V when the car is running. The ECU would most likely cutout with anything lower than 7V.

The multimeter should have the black lead in COMM socket and the red lead in V/mA socket. Not the 10A socket.

The ECU doesn't control the charging system, it's completely separate. The MINES ECU will be a direct plugin so the stock wiring diagram/ECU can give you most of the answers. The stock ECU has the codes written on the board inside the case. Not sure about the MINES unit.

Download the 1993 diagram from here http://mr2.org.nz/phpbb3/viewtopic.php? ... 49#p125056 and cross check colours and pin outs. Keep in mind this is the USDM diagram, the JDM cars are slightly different but most is correct. If you use the diagram and look at the car it's easier to figure out.
Page 56 has the charging system which only really consists of 4 wires/circuits. Charing issues can be hard to pin point but the battery can be the problem too. Hopefully not the problem with yours.

Things to check

Main wire (White) direct to battery. This has a 120A fuse in the front of the car that if you ground the white wire on the car body with the battery connected it will blow. First hand experience.
7.5A ALT Sensing Fuse
7.5A ECU-IG fuse. If this was blown the car wouldn't run though.
Charge light in the dashboard. Some cars won't charge if this bulb is out. Not sure if this is true in the MR2.
Voltage regulators car go bad. Yes it's new but new parts can be faulty.
The rectifier can go bad even in a new alternator. Had one die on me 4 weeks after purchase.
Brushes and slip rings.
The last three things are normally associated with old alternators.

Does the CAT temp sensor light and the Intercooler fan light come on when the car runs? The NA cars also have a volt meter where the boost gauge is and this can assist in telling you if it is charging. This is no help to you but for others with NA cars who might read this.

Hi really old thread bump, but my cat light and the temp sensor light came on at the same time and tonight my car nearly stalled when I was parking up and I noticed my speedo flickering when I used my indicator amd my speakers turned off by themselves...

What does the two lights on mean? My cat was deleted and cold and my temp fan runs no problem so not sure why they are on.

When the alternator dies the electrical system voltage is too low to run some things. Such as the cat temp sensor setup. Regardless if you have the cat or not the wiring for the system is still there. I cut my sensor off and the light doesn't come on.
The second light is for the engine bay cooling fan or intercooler fan depending on what model you have. Again this system can't operate with low voltage so the light shows up. You will also have a battery light.

I have had the same thing happen with the speakers/stereo shutting off especially if you have the lights on.

Time to get a new alternator or have it rebuilt.

[Ballist1x]

Yes this is exactly what I see. Thank you.

Red battery light, cat light, intercooler fan light.

When it first happened I was at traffic lights and the lights came on. As I pulled away (raising rpm) they went off.

So I pulled over not knowing what the lights all meant at that moment. Let it cool down etc and then drive it home (5 min drive).

Thing is, the fan does work.

Battery voltage was 11.9 when I checked last night but I didn't test with the engine running.

The car has a new alternator not long ago too (previous owner). I will do more testing tomorrow in daylight.

Thanks again.