My 2005 MCS 6spd is going into limp mode usually when accelerating. At idle, if I rev it a little the battery light comes on. I'm thinking it could be the crank pulley or the alternator. I'm getting a good strong 12.6v on the battery with the engine off. With the engine running, voltage is jumping from 12.2 to 6 to 11... Is there a way to test the alternator in the car, without the influence of the belt? I'm trying to test the alternator without getting a false - bad reading that could be caused by a bad crank pulley.

 

I'm no expert, but since it's the belt that runs the alternator, I don't think you can test it without the influence of the belt (experts might know better, though.) You might have to pull the alternator and take it to be tested (might be some stores in your area that can test it for free).

I would also check your belt tensioner. If it's failing, seems like a loose belt could cause the alternator fluctuation, and I know from experience that it can send you into limp mode on acceleration.

 

Check your ground straps as well as they do work loose sometimes. They will cause the car to go into limp mode due the power changes. With such wild fluctuations in the voltage that is where i would start first.

 

I was checking voltages again, car off, car running, and at 2000 RPMs. I was getting increasing lower readings, then started smelling burning rubber. Looked at the alternator and crank pulley and the belt wasn't moving, but the crank was spinning. Guess I will be looking at posts on replacing the crank pulley now. Thanks for the tips.