I was sitting outside a take and bake pizza place waiting for my son, had the truck running because it was only -6 today. Heard this weird sound from the back somewhere. Thought it was a car next to me. Later on our trip home which is about 25 miles we were at a stop light, the truck was idling a bit rough. Heard that sound again and it smoothed out. Drove another 15 miles and stopped for a pack of smokes , and heard it again. Came from the gas cap I think. What do you suppose is going on? Maybe I need a new cap?

 

Which truck?

 

Sorry it was the 98. The 92 is parked for the winter and the 48 is a project. The 98 is my DD now,only had it about a month or so.

 

I assume your talking about some type of backfire thru the exhaust ? Not a misfire or stumble ? No code on the dash (light on?)

 

Hey Steve, sounded like it came from the gas cap. I'm digging through my Haynes manual to see if it will say something about tank pressure.

 

Well the book says something about the EVAP system. A Vapor Management Valve. Then there is a canister back by the fuel tank, some hoses and a sensor. It also talks about it being hot out and causing pressure in the tank. I wish that was the problem. -6 yesterday and -9 today. It says the system is supposed to collect vapors when the truck is not running or at idle. Then deliver them to the engine when running. Seems to happen when it's at idle. I think I'll have to get it in my shop and do some poking around.