Engine/Transmission (1998.5 - 2002) Vacuum in fuel tank

[jhinkle]

Has anybody had any trouble with a vacuum in the fuel tank. When I stop for fuel I have to pull on the cap to get it off,if there is a vent to prevent this where would it be located or what other options have I got













_________________________________________________________________98. 5 24 valve 5-speed 285000miles stock, pulling travel trailers

 

[Beast2B]

isn't the cap vented? i've never checked my truck, but it's pretty standard. someone near their truck? go suck on the cap and see if it's vented! C'MON, do it for the team! maybe check a new one at a parts store.

 

[Beast2B]

also found this thread:

https://www.turbodieselregister.com/forums/showthread.php?t=122398&highlight=tank+vent

 

[Thomas]

Inspect the fuel tank rollover valve for restrictions or that the shipping cap has not been left on the end of the valve.

 

[SHobbs]

The shipping cap is red I believe. Good friend of mine was under his truck one day and noticed his fuel tank was collapsing in on itself. He asked me to look at it and sure enough there was that little red cap on the rollover valve. I removed it and you could hear the tank give a sigh of relief. It returned to it's normal shape afterwards. This cap not being removed has led me to believe that a certain number of L. P problems could be related to it. My friend had numerous problems with the L. P until we removed the cap and his truck actually ran better and had better fuel pressure. JMHO. Crawl under the truck from the passenger side and look at the top of the tank, if there is a red cap remove it and see what happens. This was supposed to be removed when it was installed at the factory.

 

[GKinney]

plugged vent

Jhinkle... . if you find no cap on your vent... it is probably plugged up with dirt. Mine did the same thing and yes the caps are vented, well at least my locking one is. But in the winter it gets moisture in the key hole and freezes shut. When I discovered my vent was plugged, I took the advice from a fellow member on here and just gave the plastic tube on the vent a small shot of air, cleared it out nicely. Good luck.

 

[jhinkle]

Ok ,thanks will check vent on tank,cap is vented but it relieves the pressure in the tank,it don't relive the vacuum from the tank

 

[Beast2B]

jhinkle, any smog gas cap is opposite of what you said. it must relieve the vacuum (allow air in) but NOT allow air/fumes to escape.

 

[Thomas]

... it must relieve the vacuum (allow air in) but NOT allow air/fumes to escape...

The model year 2000 parts catalog shows a single fuel filler cap (P/N 5278632AA CAP, Fuel Filler) for all Rams, gas or diesel.



The model year 2000 Factory Service Manual mentions the following about fuel tank filler tube caps:



OPERATION The loss of any fuel or vapor out of the fuel filler tube is prevented by the use of a pressure-vacuum fuel fill cap. Relief valves inside the cap will release fuel tank pressure at predetermined pressures. Fuel tank vacuum will also be released at predetermined pressures...



I think the cap relieves both pressure & vacuum.

 

[jhinkle]

I taken the check valve out of fuel cap and going to try that and if it works i will get me a new cap that is vented for vacuum. Thanks guys for all the good information.

 

[Beast2B]

Thomas, do they mention anything different for Cali trucks? i wonder if the cap is one of those small details for us...

 

[Thomas]

Thomas, do they mention anything different for Cali trucks? i wonder if the cap is one of those small details for us...

There is but one part number in the parts catalog for the fuel filler cap. There are parts - the ECM for instance - where there is a different part number for California Rams.



Here is how I see the fuel tank vent/fuel filler cap setup:



The tank on diesel-fueled trucks is vented to the atmoshpere via the vent at the rollover valve on the fuel tank. The only need for the relief valves inside the cap (mentioned in previous post above) would be in case the check valve/vent at the tank (rollover valve) became blocked. This blockage could be caused by a red cap left on the vent at assembly. This source of blockage has been documented in TSB's. I've never read of a red cap left on the vent stopping the mighty Cummins or totally collapsing a fuel tank-probably because of the vacuum relief valve in the filler cap.



The gasoline-fueled trucks have a similar setup, with the following differences. Trucks with 35 gallon tanks have two rollover valve/vent assemblies. The vents are not open to the atmosphere. They are plumbed to a source of engine intake vacuum via charcoal cannisters.



The gassers need an emmision system on their fuel tanks. The diesel trucks don't.