Vehicles using the enhanced vortec V6 engine may be hard to start run poorly and/or use to much fuel due to a fuel leak inside the intake manifold plenum. Commonly this is caused by a leaking fuel pressure regulator or fuel line. The fuel system will need to be pressurized with the upper intake manifold removed in order to determine the exact cause of the leak. Removing the "tuning valve" from the upper intake can allow for limited visual inspection without removing the upper intake manifold.
Car Problem Reports
GMC Sonoma Engine Running Rich Due to Fuel Leak Inside Intake Manifold
GMC Sonoma Problem
Engine Affected: 4.3L V6
Visitor, 1994 GMC Sonoma, 4.3L V6, 146,000 mi
poor engine performance & gas milage. Took out the variable tuning valve in the upper air intake plenum and could see & smell gasoline. could also see extremely clean spots inside the intake manifold where gas had been spraying (instead of a black carbon deposit coating). Replaced "Spyder Injection" (found in 1992-95 Chevy/GMC V-6's that have a "W" vin#, or a "W" for the eigth character the the vin#)