Battery Voltage drop at higer revs - 99 Taurus

Brushes... really. They are probably available. Can usually happen between 125 and 190 kmiles

It ALSO COULD be the VR, but that's classic of worn brushes. But IIRC the charging voltage SHOULD be about 14.3 to 14.6

Hey thanks for your quick advice!! The car has 72K on it, low for the year, my wife does about 8k a year.

Something always seems to 'go wrong' on these long trips. I suspect it's because I'm the driver on long trips and she simply doesn't notice the early warning signs.

Oh OK. I'll get the charging voltage checked independently, the ODBII system may not be well calibrated after 7 years of operation. Will changing the brushes help the average charging voltage also? Changing brushes sounds cheaper than buying a new alternator, just a little more work. I'll check online as well as ask at an auto parts store.

Thanks again.

JP

Sounds early for brushes... go to google and search for my alt refurb article. Also check autozone's site to see if your Alt is the externally/PCM regulated 'new improved' type.

Your brushes are worn out and/or sticking.

If the car just gets knocked around town as a "wife's car" 72000 miles can have the equivalent run time of a highway driven car with almost

Before you buy anything, i would clean the battery cables at the battery. check every high current power cable for corrosion and connection torque. Check the large high current wire at the alternator for a good connection.

How often does the car run at 4000 RPM +?.

Bob

loose belt ... under high rpm the alternator fan speeds up creating more load maybe the belt is slipping ... otherwise its the brushes .. the slip rings on the stator are not round or the brushes are so worn there is not enough spring pressure and at the higher rpm the contact is not good enough

All checked good with Battery and cables. Exchange alternator fixed it up. Charges at a higher voltage now.

Rarely. Just when passing and needing the kick down. Typically cruises at 2500-2700 on interstate.

JP

Your memory is right. Now charging at 14.3 with exchange alternator.

Glad I caught it early before it let my wife down one day.

JP

I had the same problem with a 95' Escort. The charging light would come on when the engine speed went over 2000-rpm. Changing the alternator fixed it.