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: 171,875 mi (135,000 mi - 210,000 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.
Visitor, 1994 Infiniti Q45, 210,000 mi
I found out that my fuel pump was faulty in my 1994 Q45t a few years ago. I took it in for service due to the lack of power on acceleration AND the fact that it would not simply glide or float on the freeway anymore when I eased up on the gas pedal, instead it would rapidly slow down almost as if I were applying my foot on the brakes. was absolutely flabbergasted when our mechanic told me how much it would cost to replace it. EVEN IF I bought the fuel pump from Auto Zone myself, he would be charging me $575 JUST FOR THE LABOR because the repair involves dismantling the entire gas tank and opening it up since the fuel pump is housed INSIDE THE FUEL TANK!!
Visitor, 1995 Infiniti Q45, 162,500 mi
...not fixed yet, but experiencing identical symptoms. Getting some 'backfiring,' (twice recently) also, on accelerating. And, once while starting low gear car came to a near-stop; I pulled over, waited 3 seconds, took off again and no problem.
Visitor, 1992 Infiniti Q45
My car one time decelerating. And shut down with the steering wheel locking up