More trouble

[paulg23]

Overcharging.

Now the autobox fuse is no longer blowing it is overcharging!! Noticed it because I thought it was overheating but each time I stopped to take a look the temp gauge immediately dropped to normal. Any way. 16.5 volts idle, up to 19 volts revving. Wiring all seems ok as far as I can see.
The alternator has a control terminal G... anyone know how this works. Tried disconnecting the plug on the ecu with the G and FR terminals on it but made no difference.

By the way the power steering pump has been leaking but front of alternator doesn't seem to have any fluid on it.
I have checked all fuses.

(sorry about the spelling)

[fassi1]

Seems like voltage regulator is playing ?
What'sthe voltage when engine is off ?

[paulg23]

What'sthe voltage when engine is off ?

If you leave it for a while its 12.7 volts.

[Davezj]

yes i would say the voltage regulator on the alternator is at fault. i believe you can replace the voltage regulator on most alternator without replaceing the full alternator. but not sure if the VR4 one is replacable or not.
i will have a look at ASA and see if it is list as a separate item.

over charging the battery for long periods will trash your battery if left unfixed.

part in pink MD619268 regulator alternator
but you will have to take the alternator apart to get to it.

ASA alternator.jpg

[paulg23]

Thanks for that. MD619268 is available on ebay for around £25. Little concerned about how the G wire works as I have read about people changing alternators and having the same issue. Also car is cold spec (should have said). Not worried about reduced amperage as long as this part will fit.

[paulg23]

Been doing some research and it seems the G pin is used by the ECU to reduce the alternator output voltage (to around 12.5 volts) when the battery is charged and there are no extra loads turned on (lights, A/C, etc) such that the battery is not overcharged (kept at around 14 volts). So an alternator output above 15 volts would appear to suggest it is indeed a problem with the alternator.

[Davezj]

15V is a bit of a maginal value. i have seen batteries chaging at 13-14.5V ish happily. 16V-19V is properly over charging.

so your 16-19V value is way to high.

the alternator gets grounded to chassis and battery -ve terminal via the engine block and the big gauge wire that runs to back to the battery from the gear box bell housing bolt and through the braided wire stap from the plenum/accelerator cable mounting point to bulkhead/chassis then from chassis next to battery back to the battery via the large gauge wire.

if you have a dodgy ground connection it might upset the charging of the battery. it is worth checking the earth wire just in case it has any input to the problem.

for instance if you forget to connect the chassis wire near the battery to the battery terminal, a lot of the cars electrics get grounded to the battery through the engine block via the braided wire strap from the bulk head to the plenum chamber. which is never a good thing.

[paulg23]

Thanks. I'll check that before spending any money.

[paulg23]

Checked the voltage between the battery negative and the alternator casing with the engine on fast idle. Reads 0.14 volts so I guess earthing is OK.

[fassi1]

Turn the engine off and check 2 things:
1. resistance between alternators ground (earth) and bettery negative
2. Voltage between alternators ground (earth) and bettery positive
Repeat 2. with engine running (idle).
There should be no voltage between battery negative and alternators casing and your reading is ok, but that doesn't tell anything.

[paulg23]

alternator case to battery positive = 12.1 volts with engine off.
alternator case to battery positive = 19 volts with engine running (fast idle).

[fassi1]

How about resistance between alternator's casing and battery's negative with engine off?

[paulg23]

0.2 ohms.

Have a new regulator so weather permitting will fit it this weekend.

[fassi1]

So the earth to alternator is good and it sounds like it's regulator failed.

[paulg23]

At last. Fitted new regulator to alternator. Got it all back together. What a bitch of a job! Working fine. Time for some fun again.