Okay, a little update here....the 5 gallon tank is installed in the trunk...the intake filter screen is not clogged...when we replaced the tank we checked this and it looked brand new...replaced all the fuel filters....and i don't think i can get the hose clamps any tighter...how can i tell if the valve is clogged...just take it off and look at it?

Yes, I would think you could take it off and see if air passes through it with no problem. Also, it would be a good idea to check the line going forward, that it attaches to. This could probably be done easily with a mightyvac.

Are getting any kind of suction noise when you remove the filler cap? With the symptoms you describe, I would think this would be very noticable. Maybe, a quick and easy test would be taking it for a quick drive without the cap.

A quick thought that came to mind, would be inspecting the hard lines that run from the tank to the front of the car. Possibly a kink in one of those? (Which would include the vent line.)

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Sam

84 300SD 350K+ miles ( Blue Belle )