Does an Evap Leak cause BETTER gas mileage?

[JEDI]

2005 mazda3, 200k miles

check engine light came on almost 600 miles ago.
P0455 Evap leak (large)

- I tightened the gas cap and cleared the CEL. code came back after 100 miles.
- After fill up, I bought a new gas cap and cleared the CEL. code came back after 100 miles.
- After another fill up, I Replaced the purge solenoid valve (psv) and cleared the CEL. code came back after 100 miles.

car used to avg 32mpg doing 70% hwy/30% city.
the past 2 fill ups at my usual gas station, I'm doing 36mpg driving the same. (it's sept so gas is still summer blend in VA.)

Would a large evap leak cause an increase in mpg?

 

[Bartman39]

Would a large evap leak cause an increase in mpg?

Not normally...? Or I would not think so...

But some thing to check would these...?

• Distorted or damaged Fuel Tank Filler Neck
• Torn or punctured Evaporative system hose(s)
• Defective Fuel Tank Sending Unit gasket or seal
• Split or damaged Carbon Canister
• Defective Evaporative Vent Valve and/or Evaporative Purge Valve
• Defective or damaged fuel tank
• Defective Fuel Tank Pressure Sensor

Most common items...

 

[Viperoni]

I wish mine did! I have exactly the same issue as you, which happened to start of with the minor leak version of the same code (P0442).

 

[tortillasoup]

2005 mazda3, 200k miles

check engine light came on almost 600 miles ago.
P0455 Evap leak (large)

- I tightened the gas cap and cleared the CEL. code came back after 100 miles.
- After fill up, I bought a new gas cap and cleared the CEL. code came back after 100 miles.
- After another fill up, I Replaced the purge solenoid valve (psv) and cleared the CEL. code came back after 100 miles.

car used to avg 32mpg doing 70% hwy/30% city.
the past 2 fill ups at my usual gas station, I'm doing 36mpg driving the same. (it's sept so gas is still summer blend in VA.)

Would a large evap leak cause an increase in mpg?

Well the EVAP system uses a vacuum hose so if you have a disconnected vacuum hose, that will lead to a vacuum leak which yes it can improve fuel economy.