Hey guys! Here's a good one for you.

We replaced a customer crankshaft pulley and upper engine mount on a customers 2006 Cooper S with automatic transmission. Test drove the car for 2 miles and everything was good. Customer couldn't pay for the repairs right away so it sat in the shop for a month collecting dust.

A few weeks later, we test drove the Cooper S again and experienced harsh up and downshifting and going into reverse. No faults found in the control unit. Transmission level is good. Checked charging system at idle and shows 12 volts. Revved the engine and it goes up to 14 volts and down to 12 volts at idle. We replaced the alternator with a Denso remanufactured unit and still have the same two issues.

I'm pretty sure the harsh shifting has something to do with the charging voltage but never really had an issue with a new alternator.

Thoughts?

 

Have you checked the voltage regulator?

 

Didn't bother checking the old one but the Denso alternator that we installed already comes with a voltage regulator. Technician is going to try and inspect the connector and wiring harness that goes to the alternator.

 

UPDATE: The Denso alternator that we installed is now showing 14 volts at idle now. The harsh shifting was a pre-existing condition that the customer forgot to mention to me before we replaced the crank pulley.