"vapor lock" symptons

[cherokeedust]

Has anyone figured out why S-10s and Blazers with 4.3L engines experience vapor lock-like sypmtons in hotter weather? Runs worse the more fuel you give it. Replaced everything and still dies after 20 minutes on the road. Runs great in cool weather with a full tank of gas. Several owners having the same problem. Any input greatly appreciated.

[old_master]

First thing to check is fuel pressure and leakdown both at the service port, and at the fuel filter outlet. When checking at the fuel filter, all pressure and flow must end at the tester with no fuel allowed to the engine. Depending on the year, specs are different. All readings are taken with the engine off. Regulated fuel pressure at the service port, and maximum pump output pressure at the fuel filter, are both taken while the pump is activated. Leakdown readings, at both locations, are taken 10 minutes after the pump deactivates. With the design of this system, fuel is constantly circulating when the engine is running, so vapor lock is not possible. Low fuel pressure and or volume, along with excessive leakdown can cause issues though. 1996 and newer will experience symptoms like you described when aftermarket fuel pumps are used, (the pump needs to be AC Delco or Delphi only).