Pontiac Repair: 93 grand prix chug, crank shaft, correct signal

Question
the car runs fine in the mornings for about the first 7-10 miles, but then develops a chug. You can accelerate and it won't return until you let off and try to maintain that speed or give it a little gas. chug gets worse the longer you drive. has occasionally come out of it and ran like a champ later on (very rarely). The car is a 93 Grand Prix w/ 3.1L and 153,000miles. Has new plugs, wires, fuel filter, injectors replaced with used ones(initial thought of problem after diagnose), new fuel pump 2yrs ago, 38psi fuel pressure, NO check engine light. Any thoughts??

Answer
Hey Jim:

It could be a alot of things. Possably a restricted exhaust (cat converter) do a back pressure test when it's acting up. You could have a fule pump issue where it has enough pressure but not enough volume. When the pump warms up it could actually be slowing down and thus not enough volume.. It coule be a wiring issue to the pump causing theis due to high resistance in either of the wires. Lastly an ignition system issue. Maybe a crank shaft sensor is starting to go bad or the harness betweeen the sensor and the module has high restance and the module is not getting the correct signal when the car warms up. just a few thoughts. Good louck :}