Gas cap on F150 throwing a code and dorkin up engine??

[TheDog]

First off it's a 2003 F150 supercrew with the 4.6.
I know this sounds retarded but I found out I had a faulty gas cap today. I don't know how a gas cap can be faulty though. The tech who put the computer reader on said that if the gas cap isn't secure, the pressure in the tank or something will make the fuel run weird to the engine or something. Does that make ANY sense at all? He said the engine may not run right with a faulty cap. The engine did ping a lot on 87 and I don't know why. I haven't driven it enough yet since I got it out of the shop to see if the ping is still there or not. Needless to say the check engine light is off now. I would think there should be some validity to it if Ford is going to make it a point to have the check engine light come in for just a lousy gas cap.
Comments??

 

[Shadrack]

Never heard such a thing before?

 

[NRM90GT]

if the gas cap is loose, the vapor pressure sensors in your gas tank will detect a fault in your evaporative emmisions system. this systems circulates vapors from the tank into the engine to be burned, however, it does not effect fuel flow or engine effifiency.

 

[TheDog]

Hmm... that sounds really weird. So it recirculates the vapors to be burned? So that wouldn't make my engine ping then if it wasn't working right? Any engine damage over time if I had just left it? I now have a new OEM gas cap for $24

 

[bimmertech]

if the gas cap is loose, the vapor pressure sensors in your gas tank will detect a fault in your evaporative emmisions system. this systems circulates vapors from the tank into the engine to be burned, however, it does not effect fuel flow or engine effifiency.

when you have any kind of evap leak and the ecm finds you have reduced pressure in the gas tank, it will not allow the purge solenoid to enter HC vapor into the engine.

In my years as a tech i have never seen a gas cap cause driveability issues.

if you have a ping you most likely have a different issue.

 

[JRPony]

The fuel vapors are sealed in the fuel system by the gas cap. These vapors eventually work there up to the charcoal canister and are stored in the charcoal. The ECM will then purge these vapors using manifold vacuum into the engine to be burned.
This is nothing new. Since the 80's, car manufacturers have had systems in place to manage evaporative emissions (fuel vapors). Since 1996 (OBD II), all cars sold in the US are required to have the evap system monitored by the ECM, which also includes the gas cap. A loose or faulty gas cap (P0442) is the #1 reason why a check engine light would come on in a 1996 or newer car. Without a new gas cap, your truck will not pass smog.
BTW a fault in the evap system will not cause an to ping and will not cause the engine to run poorly.

 

[TheDog]

ok so its a worthless code basically and has no affect on anything. good to know. I'll keep you posted

 

[wythors]

Loose or defective gas caps are a very common "check engine light" issue on modern cars. I've seen it for years in the dealerships I've been in. In the state of Washington a pressure check of the gas cap is a part of the emissions test. If it fails, you have to buy a new one before you can get your tags. Been there, done that, have the t-shirt.

 

[TheDog]

so the emissions are worse if the gas cap is faulty? dang

 

[Black1987Stang]

In the state of Washington a pressure check of the gas cap is a part of the emissions test. If it fails, you have to buy a new one before you can get your tags.

Unless the place doesnt check the gas tank lol The shop I used to work at did certified state inspections and when it was time to hook the cap up to the cars gas tank they had a glass jar nearby and they would put the test cap on that instead of the gas tank

 

[HISSIN50]

The Dog, the thing with the EVAP system check is to keep petroleum vapor out of the atmosphere (it should not actually effect the engine emissions if the cap is not sealing). And this aint all bad - as Jrichker points out, if you park in a garage with a gas water heater, etc, that could be bad. I find it ironic that the Canister purge discharge line is the first line to rot on a 5.0L.