Oldsmobile/Buick Repair: Fuel guage and check engine light pattern?, fuel guage, delta 88

Question
Hello there. I'm driving a 1996 Olds Delta 88 3800. I've been noticing lately that when I fuel up I'm sitting at 1/4 tank of fuel. Then, from the duration of 3/4 tank of fuel to 1/2 tank of fuel, the check engine light is on. Once I cross the 1/2 tank or less margin, the light goes off. Any ideas? I've been wondering if it might be the baffer, but am not certain.

Also, I've noticed that as of late, when I first accelerate, the engine seems to lag in power, but once I hit around 50kmph, the car accelerates far too fast to control, throwing me back in my seat. Any ideas on this one too? Thank you so much in advance for any help with this.

Answer
Hi
I would advice FIRST to take the car into a repair shop, and have the computer scanned for codes (check engine codes).
We could then see if there is any relationship between the check Engine light and the fuel level. Some system diagnostics are ran only when fuel level is between .75 and .25 (EVAP system is one).
So my best advice would be to get the codes and post back, I'll be HAPPPY to assist as much as possible.
I do hope this helps.
Good Luck
Pawl