I have a 1995 chevy blazer 4.3 that is missing bad. No codes. Just changed the fuel pump. Direct pressure on pump is in the 60s but when hooked to the Schrader valve its like in the 59s and when running its in the hight 40s to low 50s. My guess is that's whats causing the misfire. but what would cause this other than fueal pump because it is new. Its not as bad when going highway speeds but its sucking down gas and has a little time accelerating unless I give the pedal a good press please anything to help would be great.

 

Just because the pump is new doesn't mean its not JUNK! As with tune-up parts I wouldn't use any thing but a Delphi or Delco fuel pump. Do a search on how to test fuel pumps.

 

Unplug the MAP sensor see if it still does it, if so, get a new one. An MAP sensor is to the left of the spider injector plug and has three wires.

or the distributer, wires, and spark plugs

the cat or air filter

vacuum leaks

it goes on and on