I have a 2004 monte ss 3.8l supercharged, and have a starting problem. It will not start unless U press footfeed down about half to three quarters of the way down. Trys to start a little without but will not run. Have checked fuel pressure, 50psi. Changed maf,no change. Seems to idle a little rich. Changed engine and did the same in the other car before I pulled it out. I replaced all upper gaskets. before installing. Appears to be loaded up when starts and has a misfire until it clears out, accounting I think for only code of misfire in scanner. I suspected the throttle positions sensor, but has .43 on scanner and move with footfeed movement. I would appreciate any help I have exhausted all of my thoughts. Thanks U

 

Wait you changed an entire engine and the problem persist? Only thing I can think of is fuel pump, fuel vapor canister or maybe even an ECU/PCM faulty.