Gran prix hesitation

I have a 95 grand prix se. When the fuel gets low and it is warm out it hesitates and idles really rough.Fuel is at about a quarter tank. I replaced the knock sensor think this was it from a friends advice. didn't work. It is definatley a fuel problem I think. I can put full tank of gas and some drygas and it runs fine. Any other ideas? Injectors or dirty fuel tank. Oh and I replaced the filter already.Thanks

Does the hesitation ever occur when your are trying to accelerate after coming off a ramp onto the interstate? I had a similar problem and it turned out to be a bad valve in the tranny. It seemed to just act like it was starved for fuel but what was happening is that the tranny wasn't able to downshift due to a lack of oil pressure due to the defective valve in the tranny. If not, have you checked fuel line pressures?

I think your fuel pump may be giving out. Anything under 1/4 tank of fuel, and the fuel pump isn't submerged in fuel, so it heats up. Have a fuel pressure and flow test done on it when it's low on fuel again.

Also check for evaporative emissions codes if the Check Engine light is on. When youget low on gas, there is more room for the fuel to build pressure in the tank by expanding. If the evap system isn't working properly, this pressure will cause a vapor lock situation, which could result in the symptoms you describe.