I was looking under my truck today and noticed a box under the bed. it has a wire connecting into it. its right behind and above the spare tire. its about the same shape as a fluorescent light ballast, but maybe twice the size.

any ideas what this is?

thanks,
sal

 

I don't know what year truck you have and i haven't worked on many of the new models but my guess would be a charcoal can or something for emmisions??

 

its a 97 f150.... good answer, i'll bet you're right

 

fuel system ?? or...maybe somthing to do with the towing plug....

 

It is part of the pressurized fuel system. When I threw a light for that, the tech said it was either my fuel cap or that canester under the bed. I got lucky and it was the fuel cap...

 

Must be the evaporative emissions canister then. It basically has some sensors and a couple of vsv's to apply vacuum to the fuel tank to keep fuel vapor from escaping into the atmoshere. The bad thing is that unless you have a plastic gas tank, all tanks tend to rust and leak after about 10 years. If your tank can no longer hold a vacuum you will get the check engine light all the time.

-Jon