Fuel Tank holding pressure

[Cincinnati Guy]

I had my truck out doing some grunt work this morning hauling fire wood. I got back home and thought one of my brand new tires were leaking air, but no it wasn't. I removed the rear fuel cap and the whistling air sound went away. I have the non locking caps. Can a bad fuel cap make the truck run slightly rough? Is it somewhere else making it hold pressure or is the cap bad?

 

[6 Nebraska IDIs]

My brown truck has been doing that as well lately. I know with gasoline engines it can cause issues with how the engine runs, but I don't know about the system in our trucks.

 

[Diesel_brad]

The cap should be vented. Sounds like you need a new one

 

[Dsl_Dog_Treat]

I would be checking the breather tube for the roll over valve as it sounds like it is plugged.

Mud Dauber wasps have a nasty habit of forming their nests in nice cozy little orfices on vehicles around these parts.

 

[subway]

I would be checking the breather tube for the roll over valve as it sounds like it is plugged.

Mud Dauber wasps have a nasty habit of forming their nests in nice cozy little orfices on vehicles around these parts.

yup, it also affects filling the tanks. the vent is in the middle of the tank at the top and it should have a short length of tubing coming off of it. the tank was probubly not pressurized but had a vacume on it from the fuel that is used to run the engine.

 

[icanfixall]

I think the two above postings are correct. Find the tank rollover vent. Make sure the line is free and open so air can be drawn in or pressure can escape thru it. Or leave the fuel tank caps loose...

 

[badaceds650]

just a thought but if you have a stuck injector it can release combustion pressure through the return lines into the tank and pressurize the tank

 

[franklin2]

Anyone who has one of these trucks, should have already done the vent mod to the top of each tank. That is, taking the roll-over valve completely out, putting a short elbow fitting into the roll-over valve grommet, and then running 1/2" line from the fitting and then up to and tying it to the filler pipe with a loop. With a 1/2" line there is no way pressure is going to build in the tank, I don't care what type of cap you have. And it makes filling the tank at the station so much faster with no foaming and fuel splashing up cutting the nozzle off.

 

[bghnkinf350]

I took out the roll over valve, put a half inch rubber hose inside the grommet with a fitting inside it and hose clamp holding it on to keep the hose from pulling out. I ran the hose up, then put steel wool in the end as a filter. The truck runs better.

 

[Exekiel69]

I would be checking the breather tube for the roll over valve as it sounds like it is plugged.

Mud Dauber wasps have a nasty habit of forming their nests in nice cozy little orfices on vehicles around these parts.

I agree, they make a mess on the breather hoses on tanks and axles around here.