Alternator not charging until revved.

[C.P 0]

My corrado developed this problem fairly recently. It's an 89' 1.8 16v.

The alternator doesn't charge until you rev the engine over 4000 RPM, just once, then it's fine the whole time it's running. when i measured the voltage, i get ~12v when the engine is off, ~9.5 when the engine is running but not revved, ~14.4v after it is revved.

 

since the problem started, i have done the following;

replaced the alternator with a recon 90A one.

tried 3 different voltage regulators (the one that came with the new alt, the old one and another brand new one i had).

made sure the belt is tightened correctly.

cleaned all the wiring connectors for the alternator and all the earth points.

 

Does anyone know what the problem could be?

[Wullie 1]

I have a similar problem but only need to rev it to1200 rpm now. Initially I needed to rev it to about 1500 so I fitted a new regulator, drive belt, cleaned up any connections I could find and then finally a new battery. It's still the same. I'm waiting till the weather improves to see if it may be temperature related. I did think it may be the commutator?? (Copper bit the brushes contact) that might just be worn after 190,000 miles but haven't looked as yet though as you have changed the alternator it suggests something else. Will watch with interest any suggestions. I'm sure some of the genius's on here will provide a blatant and simple solution.

[Rob_B 0]

Mines the same. Need to rev over 2000 once and then it's fine. Never bothered me. Only done it since I changed the regulator. On a side note, turn your multimeter around so it stops reading -12!

[C.P 0]

aha, if you look carefully you'll see it's a ~ not a -, which means approximately. :tongue:

[Rob_B 0]

aha, if you look carefully you'll see it's a ~ not a -, which means approximately. :tongue:

 

My bad!didn't look that close!

[davidwort 0]

This problem usually occurs when the motor commutators are worn, so changing the brush pack doesn't always help.

Remove the brush pack and have a look at the commutator segments, brass bit where the brushes make contact, you can sometimes revive them by sanding them flat with some coarse then fine wet and dry, they get quite grooved over the years and should be smooth to form a flat contact surface with the carbon brush.