Fuel tank vacuum

[Irontrader]

I've noticed recently that my fuel tank is developing a vacuum. This is more noticible on a road trip where you fill up and drive non-stop to the next truckstop to fill up again. I've noticed when I start to remove the fuel cap that the tank has built up a sizeable amount of vaccuum.

I would think that the vaccuum wouldn't be good for the lift pump as I would think it would make it harder to pump fuel out of the tank.

When my truck was fairly new I had the red cap on the vent problem from the factory, but the dealership fixed that and even replaced the fuel tank to my surprise. The past couple of years I haven't noticed the vaccuum build up as much as I have lately.

I'm thinking now of drilling a small hole in the fuel cap just to be sure that vacuum does not build in the tank.

Has anyone else done this?

 

[Jack in Alaska]

I have the same problem under the same conditions. My dealers service mgr. said it is normal and not a problem.

 

[Pat_in_Utah]

I would NOT drill a hole anywhere in the fuel system, including the cap, without some very reliable source telling me it's ok. The system is designed that way for a reason! I'm no expert, but I know it is normal. The cap w vacuum is an intricate part of this system - just don't do it!!

Pat


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2001. 7 White Sport RAM 2500HD QC SLT 4X4 LB 3. 54 LSD Cummins Auto
My Ram Page

1999 21' Terry Lite Towable 5400# GVW
1990 Kawasaki KLR 250 Enduro

 

[KatDiesel]

Have you looked for the lil red cap on the top of your fuel tank?? Some of these were left on the trucks at the factory... ... ...

Do a search on old posts and you'll see what I am refering to. Heres a related thread with a picture Lil Red Cap

[This message has been edited by KatDiesel (Eric Howard) (edited 05-25-2001). ]

 

[PHaller]

I agree wit KatDiesel. Check for the red cap. I sucked my OEM plastic tank nearly flat until I removed the red cap. no more "giant sucking sound" and my tank no longer deforms.
-Paul R. Haller-

 

[Irontrader]

Eric and Paul:

Read the first posting and you'll see that the red cap thing was taken care of a couple years ago on my pickup.

Pat_in_Utah:

Until someone can explain why you want to create vaccuum in your fuel tank, I'll think you're off track in thinking it is better to have vaccuum than to not.

For the present time I'll just loosen the cap each time I stop at a rest area.

 

[KatDiesel]

my god I am an idiot... ... sorry bout that I missed that the first time... . sheesh... must be this nightshift thing... ... sorry!

 

[illflem]

After reading in the service manual about the fuel cap I see that it is more than a just a lid. The cap is supposed to release pressure at 1. 95- 2. 5 psi, the vacuum release is set for minus . 14-. 29 psi. These numbers are supposed to prevent major spillage in a roll over accident. Manual says to replace cap if it doesn't fall in the specs, don't know how you check it, probably easier just to replace it if you think it might not be venting correctly.

 

[Evan A. Beck]

That G0DDAMN red cap cost me a fuel tank on my 98. 5... What a pain in the @ss. DC retards... #ad

 

[Shelby Griggs]

I get the impression that an open fuel system might set a code. There is a warning printed on my cap that states "A loose cap may turn on the check engine light. " Drilling a hole might turn on the check engine light. Is there a pressure sensor in the tank? How does it sense that there isn't a cap on the filler?

Shelby

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2001. 5 2500 QC LB 4WD, ETH (Built 09-10-00), DEE, 3. 54 gears, Laramie SLT, Camper Special, Trailer Tow, Travel Convenience Group, Power Driver Seat, Alarm System, Remote Keyless Entry, Fog Lamps, Cab Clearance Lamps, HD Transfer Case, Bright White with a Gray Interior. Built 09-15-00, took delivery on 10-06-00, 12310 miles as of 05-01-01. Custom aluminum work body / flat bed. Coming soon: E-Brake and gauges.

 

[Evan A. Beck]

There's no sensor on the tank module. The fuel system is designed to be vented to the outside air. Vacuum in the tank can cause low fuel pressure, hard starting, and poor fuel economy.

The ECM and PCM have no clue if the tank is open-vented or not.

 

[Cooker]

Evan,
How did the cap cost you a fuel tank???

-Ryan

 

[illflem]

More than likely a collapsed tank. Even though I realize that the red vent cap space out can cause a problem I just wonder how it can happen if the fuel cap is also supposed to relieve vacuum?

 

[Evan A. Beck]

Cooker,

The red cap collapsed my fuel tank. Pretty amazing what a little bit of vacuum can do. On my 35 gallon tank, it had reduced the capacity to less than 31 gallons.

That's a good question, Illflem... #ad