Originally posted by lobudgetraceing:
a bad gas cap will release the wacuum from the tank and cause a check engine light.
the vacume that builds in the tank is normal.
The gas cap is meant to keep fuel vapor from being released to the atmosphere. The vapor under pressure is routed to the carbon cannister, and later sucked into the engine and burned. Fresh air enters the gas cap through a small bleed valve to prevent vacuum in the tank. Excessive vacuum in the gas tank lowers available fuel pressure.
"Those who cannot remember the past are condemned to repeat it" -George Santayana
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