Engine/Transmission (1994 - 1998) Fuel tank vacuum

[osmith]

Wondering if this is normal on a '96 ram auto?



When I open my fuel cap it is a whoosh of air going into the tank. I mean it's sucks in quit a bit of air. Should the cap vent more or what? I have a locking fuel cap on it now, but as I recall the factory cap did the same thing.



Thanks for any input. .

 

[nfox]

tank vent

I think your gas cap should be vented otherwise it will make the lift pump work harder and eventually the truck will not start.

 

[illflem]

The fuel cap should vent vacuum and pressure but there is also a vent on top of the fuel tank module whose cap is inadvertently left on on some rigs. Check and remove it. Most of the caps are red, the vent tube comes out at a 90°. There is another cap on a fitting for an auxiliary fuel line thay comes out straight, leave this one capped.

 

[B9Mile]

Mr Fritz comes through again. Here is some info about the cap.



http://dodgeram.org/tech/dsl/ISB/low_power.htm



Even though you have a '96, this may still apply.

 

[Cooker]

I had a vaccume on my tank. It was so bad it dented in the bottom of the tank. What finally fixed it was a new Rollover valve (Thanks Evan) and I think it cost ~$25. Let me know if you need a part number.



-Ryan

 

[TPCDrafting]

just curious

Does it seem to do it more when the tank is near empty or when you have a quarter tank or more? Mine sucks in a bit when it's more empty. But it's only a bit at that.

 

[osmith]

Thanks for all the info guys,



I crawled under the truck and found that there is no cap on the vent valve. Am I right in assuming that even if the cap is not vented the valve on the top of the tank should still vent vacuum and pressure? Or does one vent pressure and the other vent vacuum?





It may be that the rollover valve mentioned here is at fault. Maybe I should change this part out, I hope you don't have to drop the tank to accomplish this



BTW what does this rollover valve actually do.



Thanks again for the help.....

 

[Cooker]

The rollover valve does vent pressue/vaccume from the tank (when it is functioning properly). It got it's name from the fact that if the truck is rolled over that it will not vent fuel in the upside down position.



The valve can be changed without dropping the fuel tank. It is a tight fit but it can be done. It should take a total of 15 - 20 minutes.



I can dig up the PN's tomorrow if you'd like them.



Below is a pic of what the vaccume did to my tank.

 

[osmith]

thanks Cooker,



I actually found your old thread and got the PN from there, thanks again.



My tank looks similar to yours :--) so I've got some serious hoover action happening. My tank now probably holds 5 less liters than it used to



I'm assumning you have to spin the locknut right off of the top of the tank to replace the valve and gasket? And did you notice any change in power following the fix.





Thanks again for all the help... . what would I do without the TDR

 

[illflem]

While trouble shooting a rollover valve I connected a hose to it and was able to suck air with the the fuel cap off. Don't do this with a full tank! Might save you the trouble of replacing something that isn't broke.

 

[Cooker]

osmith,



I didn't notice any changes in performance after the fix. I think that is more common with the 24v's.

 

[Missouri Mule]

osmith,

If you bought the locking cap at local parts store and mentioned it was for Dodge Ram (diesel) it should have the same psi as the oem unlocking cap.

Dodge sells locking caps also but more expensive and gas engine fuel caps are same psi.