2nd Gen Non-Engine/Transmission Fuel Tank Filler Tube Cap

[RMcKinney]

RMcKinney 1995 2500 Stock with 274000 with Fuek Tank Cap question.
Got the Fuel lines (Feed and reurn) changed.
Got the Fuel Heater out and it has been running Great.
While i was checking for Fuel leaks(post 200 mile check) it died.
I told my son "Something just turned the Fuel Off ??".
Crack the Fuel Tank cap and I could head air running in for 3-5 seconds.
Leave the cap loose and runn fine. 1 1/2 hour home so l left the cap 1/16 or a turn loose. Stuffed some clean towels to cap it where was and ran fine all the way home.Next day with the ran in place,started ran ran fine.
Can the cap cap cause this?

 

[fest3er]

On long drives, my '98 has often had 1-3 'seconds' of vacuum, but never enough to prevent engine operation.

The service manual doesn't say anything about the fuel cap on the diesel. The gassers have a cap that will relieve excessive pressure inside and outside the tank; I expect the diesel fuel cap should do the same. Your cap probably doesn't relieve excess pressure on the outside (otherwise called 'vacuum' in the tank).

 

[RMcKinney]

Thanks fest3er,
The diesel has a popoff valve to releive pressure. The Tanks ability to make a vacuum is what has me stumped.
RMcKinney

 

[VolsFan]

There is a rollover valve on top of the fuel tank that is most likely clogged up with debris. Happened on my 99. Would make a hissing noise then crack the cap and would release the pressure. I asked about it years ago on here and cleaning the rollover valve fixed me up. Was kind of a booger to access.

 

[fest3er]

Thanks fest3er,
The diesel has a popoff valve to releive pressure. The Tanks ability to make a vacuum is what has me stumped.
RMcKinney

Where else in the fuel system is air allowed into the tank to replace fuel that has been consumed? If there is no other place, then the cap must relieve excess pressure in either direction.

 

[GAmes]

The rollover valve is also a vent when the truck is right side up.

 

[kcv67]

You may still have a cap on the breather by the roll over valve it was supposed to be removed by the dealer prep. Trying to remember form 15 years ago it was a little red plastic cap about an 1/8 diameter. I will see if I can find a post on it

Casey

 

[RMcKinney]

Cap gone Casey

You may still have a cap on the breather by the roll over valve it was supposed to be removed by the dealer prep. Trying to remember form 15 years ago it was a little red plastic cap about an 1/8 diameter. I will see if I can find a post on it

Casey

I was trying to fine air leaks in the Fuel system by applying 20PSI to the tank. I had to tape the roll over vent so the tank could build pressure.
I could hear the roll over ball work like it was suppose to when i added the air pressure.
I guess the vacuum in the tank indicates i fixed the air leak.Not very much information for the Filler cap.I've trying to get away from work to get a new cap so in the mean time i leave the cap loose and been it has been doing fine.

 

[RMcKinney]

Thanks Neal, I've been trying to get away from work to get a new cap.As far as i know this cap is 20 years old. For a cheap test i sucked on it and it was real hard to get air through. The second time it seemed ok so i that indicates it is time to get another one.

 

[GAmes]

In the '97 manual the specs for the fuel filler cap and info for the rollover valve/vent is on page 14-73. Your FSM is probably about the same.

 

[RMcKinney]

Thanks GAmes.