ok i am getting a PO440 code for my 1999 Chevy S10 Blazer. V6 4.3ltr 4X4 , automatic. First it sounded like a bad exhasut leak then we changed the regulator valves in the exhaust lines from the motor to the air pump(hate the damn thing).It ate a hole in the air filter housing,the power goes up & down ,mostly down when you push on the gas,and it becomes sluggish have done a tune up but havent changed the O2 sensors.any suggestions please?

Check for water in your evap cannister, check for a clogged cat, check your gas cap...

ok i am getting a PO440 code for my 1999 Chevy S10 Blazer. V6 4.3ltr 4X4 , automatic. First it sounded like a bad exhasut leak then we changed the regulator valves in the exhaust lines from the motor to the air pump(hate the damn thing).It ate a hole in the air filter housing,the power goes up & down ,mostly down when you push on the gas,and it becomes sluggish have done a tune up but havent changed the O2 sensors.any suggestions please?
P0440 indicates a large leak in the EVAP system
The evaporative system includes the following components:

• The fuel tank

• The EVAP vent solenoid

• The fuel tank pressure sensor

• The fuel pipes and hoses

• The vapor lines

• The fuel cap

• The evaporative emission canister

• The purge lines

• The EVAP purge solenoid

The evaporative leak detection diagnostic strategy is based on applying a vacuum to the EVAP system and monitoring the vacuum decay rate. The VCM monitors the vacuum level via the fuel tank pressure sensor input. At an appropriate time, the EVAP purge solenoid and the EVAP vent solenoid turn ON, allowing the engine vacuum to draw a small vacuum on the entire evaporative emission system. If a sufficient vacuum level cannot be achieved, a large leak or an EVAP system malfunction is indicated. The following conditions can cause this problem:

• A disconnected or malfunctioning fuel tank pressure sensor

• A missing, malfunctioning, improperly installed, or loose fuel cap

• A disconnected, damaged, pinched, or blocked EVAP purge line

• A disconnected or damaged EVAP vent hose

• A disconnected, damaged, pinched, or blocked fuel tank vapor line

• A disconnected or malfunctioning EVAP purge solenoid

• A disconnected or malfunctioning EVAP vent solenoid

• An open ignition feed circuit to the EVAP vent or purge solenoid

• A damaged EVAP canister

• A leaking fuel sender assembly O-ring

• A leaking fuel tank or fuel filler neck

Any of the above conditions can set a DTC P0440.