Truck running lazy

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by vieques, May 4, 2013.

  1. vieques

    vieques New Member

    I have a 1999 GMC C2500. Put a new engine and got the truck running again. For some reason it feels like it has no power, gas milage is about 12-13 mpg. I have change spark plugs, wires and also done injector cleaner. Check fule pressure and stay right around 50 psi. No engine lights is on but the truck still feels lazy. oh, I also installed a new K&N cold air intake.
  2. j cat

    j cat Epic Member 5+ Years 1000 Posts

    could be fuel pressure is low. 5.7L you need 60 psi key on engine off. running should be 57 psi area.

    a restricted exhaust is another common power killer. with the 5.7L replacing the distributor is a good thing to do .
  3. vieques

    vieques New Member

    I checked the fule pressure the other day and with engine of was about 55 psi. I did not checked with the engine running. I will do that next. I have flow master muffler but still have the factory cat.
  4. j cat

    j cat Epic Member 5+ Years 1000 Posts

    restricted exhaust can occur if the cat gets melted internally or the cat breaks apart and plugs up the muffler.

    remove the upstream O2 sensors . leave the holes open and see if power returns. if so then the exhaust is the problem.

    you saw 50 psi now 55 psi . this makes a big difference in engine power.50 is too low ..55 is good...
  5. vieques

    vieques New Member

    OkI will do that. i will keep you posted. Thanks.
  6. thrasher

    thrasher Rockstar 100 Posts

    If the truck has high milage & it hasn't been done already, you might want to replace the fuel filter also.
  7. j cat

    j cat Epic Member 5+ Years 1000 Posts

    good idea on the fuel filter .. a 2500 truck 12 MPG uses a lot of fuel so the filter need be replaced more often .

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