If the car drives well at cruise speed, but lacks power while accelerating, there may be a problem with the fuel pump.Google+
Car Problem Reports
Infiniti Q45 Lack of power on acceleration due to fuel pump issue
Infiniti Q45 Problem
Average Mileage: 157,500 mi (135,000 mi - 180,000 mi)
Visitor, 1995 Infiniti Q45
My 1995 Q45 would not shift into passing excelleration. I changed the fuel pump modual that did not fix it. Then I change the fuel pump and that solved the problem of excelleration.