could a bad fuel cap cause the truck to not run right?

the reason i'm asking is because my truck seems to run differently than a few days ago, even after changing the iac, and i'm having a hard time trying to find it. the reason i came to the fuel cap is because when i went ot fix the float on the fuel pump, i lifted the bed off instead of dropping the tank and forgot to take the screws out of the filler neck... luckily only the plastic arond the screws broke and the cap. because the autostores where closed at the time, i got a replacement one from my uncle for free. the only problem was he had used it and his truck failed emissions because the cap wasn't venting properly or something of that nature.

has anyone heard of this?

thanks in advance

 

I can't think of a reason why it would run bad because of a bad cap.

 

If the cap doesn't vent properly that will cause it not to run correctly, I'm 99% sure that you need to have a vented cap on all year Dakota's. if the vent isn't working right you would build up negative pressure in the tank that your fuel pump might not be able to overcome and could possibly damage the fuel pump or collapse the fuel tank it self... I haven't seen the fuel tank collapse but I have heard it’s possible, although I have seen many fuel pump and other parts of the fuel system fail because of the wrong gas cap. So go to the local Salvage yard or Parts store and get the correct one.

 

Well I'm not sure about the early yeas. But the Magnum engines has a Vapor canister which collects the vapors from the gas tank to use later. So with a functioning system you will never have vapor pressure in the tank. That system also allows air into tank so it is not going to have a vacuum in the tank.

 

ok, i wasn't sure because i heard my uncles 98' yukon failed emissions because of this cap.