When you say weak start, do you mean the starter is turning slowly? If you do, have you checked for excessive resistance in the ground wire to the engine block? Although the ground may appear to be physically good, the wire may have deteriorated internally.
I attached a pic below of the entire starting system wiring schematic. If you take a look at it, you'll see there really isn't a lot that can cause this issue other than a weak connection.
Once started, does the engine run properly? Is there anything else you can think of that may lead to this happening?
Let me know if that is what you are referring to as far as a weak start.
Sunday, October 4th, 2020 AT 7:05 PM