Quote:
Originally Posted by Beemdog
AGM batteries can lose the ability to produce cranking amps without a large drop in resting voltage. Typically you will see a large voltage drop when the starter is actually cranking over if the battery is tired. Can you have someone crank the car over while you monitor the battery voltage? When these AGM batteries decide to go, they can lose capacity very quickly, even if stored on a battery tender.
Another option is to start the car when jumped to an external battery via jumper cables and the underhood connections. If the starter cranks quickly/normally, then you know the starter is OK. Starter for an M3 is an expensive piece and difficult to get to compared to many other cars (it's buried under the throttle bodies in the Vee of the engine block), so I wouldn't change it unless you know it is going out.
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Thanks for your reply. That is what a shop I just sent this video to also said. We'll be doing a load test next week to double check.
I saw DIY instructions for the starter, and it looks too challenging for me as it is buried deep. I'm not confident yet to remove the plenum.
I'm a little confused about the underhood connections. Do you literally mean something to connect the external battery in the engine bay? I would have thought jump starting our M3s would be just to the battery in the trunk. If you can confirm, that'd be great. I don't have another battery, but do have another car to jump start off of... but not sure if that'll provide the correct amount of volts/amps necessary to start our cars.
Thanks again for your fast reply!