chrislofty

Basically this has happened now with two alternators (original and new/rebuilt) and two batteries.

Both battery terminals are tightened properly, alternator plug and wiring all tightened properly, brand new belt and crank pulley working properly etc.

At idle sat still the battery kicks out 14.7v, engine shut off the battery kicks out 12.4v.

When I drive the car that's when the battery seems to dissipate and lose charge. By the time I have done four or five miles the dash lights and headlights are really dim and once shut off it wont restart. The fans don't kick in, the steering goes heavy and I have to shut it off.

It did this once and I swapped a fresh battery in to get me home before fitting a new alternator. Worked fine until the same thing happened. I then swapped the original Lexus battery back in, let it charge and checked the output with a meter. All OK, drove it four or five miles and it died again.

I'm past myself with this now, anything mechanical I consider myself competent with. Electrics? Nah...

Any help or suggestion would be massively, massively appreciated.

Mr Jokster

iTrader: (8)

Bad voltage regulators? twice... idk

vijayn

What does the voltage on the battery say when you have load on the engine? Leave your car idling and turn the high beams on and the air con on, and then see what the voltage is.

lexo98

iTrader: (2)

Are you checking the voltage with a gauge connected to the battery or to the OBD?

chrislofty

Sorry, should have said the readings were taken with the car running as well as having headlights and main beams on.

And the readings were taken across the battery terminals only.

vijayn

I'm curious to see what the voltage is during driving. I'm wondering the voltage drops as rpms change. Are you able to measure the voltage while driving?
Other things to check would be bad ground points on the battery and the alternator (mounting point to body). Sometimes the voltage can be good but there isn't enough current to charge/deliver.

chrislofty

Will check tonight, where exactly are these please Vijay? Easy to see?
Sorry I've come from the VW thing to Lexus so I'm used to working on things about as complex as a postage stamp.

vijayn

Fair enough, Just check the mounting of the alternator to the bracket as this would be the ground for the alternator I believe.
Also check all the thick cables that are connected to the negative battery terminal and see where they go and connect to (most likely somewhere in the engine bay). Make sure these points are secured and test with a voltmeter to see if the grounding points are still good with no voltage drops. Typically the voltage drop should be less than 0.05V to be a good connection.