gas cap Q

[TorqueBite57]

what happens if you dont use a gas cap or it isnt tight? can it effect driveability or anything like that? i know it has something to do with pressurizing the system but what exactly happens?

 

[JimBowy]

what happens if you dont use a gas cap or it isnt tight? can it effect driveability or anything like that? i know it has something to do with pressurizing the system but what exactly happens?

gas will evaporate from your tank

 

[Black1987Stang]

From what I know, i dont no if it does affect our cars, or just the newer cars. It has to do with the Charcoal Canister, it pressurizes the tank every startup? or driving cycle? (forget which one). and if it doesnt pass it will light up the check engine light and throw the code for it. Im not sure exactly how it does it or if it actually uses a vacuum instead but im sure it might be able to do something with driveability

 

[JimBowy]

From what I know, i dont no if it does affect our cars, or just the newer cars. It has to do with the Charcoal Canister, it pressurizes the tank every startup? or driving cycle? (forget which one). and if it doesnt pass it will light up the check engine light and throw the code for it. Im not sure exactly how it does it or if it actually uses a vacuum instead but im sure it might be able to do something with driveability

I really don't think having a vented gas tank will cause the problems you have mentioned. The purpose of the charcoal canister was to help pass emissions. Evaporating fuel -> failed emissions

I'd test your theory about getting codes but I have an LX.... they don't have working check-engine lights.

 

[Mustang5L5]

I'd test your theory about getting codes but I have an LX.... they don't have working check-engine lights.

It's not just an LX thing

86-88 Speed Density Mustangs don't have a CE light.


The Gas Cap is for emmissions purposes only. Any fuel vapor must be combusted in the engine. It cannot be vented to atmosphere. The vapor is drawn through the charcoal canster and then up to the vac line in front of the intake. The Fox's will not throw a light, but in my '03 Mustang i actually have a "Check Gas Cap" light which comes on if i leave the cap off.

 

[joel5.0]

Running w/out a gas cap or not tight enough will not affect driveability. In OBDII systems, will let the driver know something is wrong thru the CEL illuminating, registering a code, or with the newer "cap missing/loose" indicator, but the engine will continue to run with no noticeable problems.

The only way a cap would have something to do in creating a driveability problem, is if the evap system is shut down and the cap is closed tight, not allowing the vapors to be released or recycled, causing a vacuum in the tank. This will not allow the fuel to flow to the engine eventually, the stronger the vacuum in the tank, the less fuel that will be able to get out of the tank. My 2¢.

 

[HISSIN50]

Yep, OBD-II cars are finicky about the EVAP system and will recognize a pressure delta when they cycle the drive-off diagnostics.

One other thing - I would not call it the closed-EVAP system an emissions-only device. Jrichker wisely points out that if one were running a vented tank (open system) and had something like a gas water heater in the garage, that would become a safety, not emissions concern.

 

[Mustang5L5]

Jrichker wisely points out that if one were running a vented tank (open system) and had something like a gas water heater in the garage, that would become a safety, not emissions concern.

Yup, Gas doesn't explode...it's vapor does!

 

[JimBowy]

Yup, Gas doesn't explode...it's vapor does!

Tell that to the guys who delete their charcoal canisters