Battery drain and rev counter fault
Hi all, first post on this forum. Recently bought my second 156 V6 and it has a charging problem. The car can sit for days or even weeks without draining the battery so I am fairly convinced it doesn't have a short anywhere, but when you run the engine it will go for about an hour or so then die with a flat battery. The previous owner sold the car with this fault claiming he has had the alternator checked and it came back all clear but the symptoms point directly to that being the fault.
The alternator has excitation voltage going to it when the ignition is turned on and the charging output terminal is definately connected to the battery positive terminal.
There is a lot of talk of a rev counter fault causing battery drain when the car is parked, but like I say I don't have that problem. The only thing that makes me wonder about the rev counter is the battery warning light never comes on, even when you first key on when all the other warning lights come on, so I am wondering if there is some link there.
I've monitored the battery voltage with the engine running and it sits around 12v and drops slowly as you turn on lights and wipers etc. Revving the engine doesn't help matters.
Like I say, all the symptoms point to the alternator being faulty except that the previous owner insists he had it tested and has sold the car for a song based on the fault beating him.
At some point I saw some photos of the rev counter PCB with the faulty chip arrowed, but I can't find them now, does anyone know which chip is the culprit? There are no obviously dead ones on my board.
Sorry for the lengthy post and hopefully someone can help.