Is the fuel system pressurized or under a vacuum? I'm almost sure it's pressure and if it is how do they pressurize it. I'm having trouble with my aux fuel tank setting the loose fuel cap alarm. I only happens when it's empty and the main tank is at half, I think its a volume thing but not sure. The only thing I changed when I installed it in this truck is I removed a piece of plastic that was blocking the vent line, I may have to block it back off. I vent into the vapor recovery line in the filler neck.

Denny

 

the vapor management apply vacuum to detect leak in the system by closing the vent selenoid at the vapor canistor.A sensor on the fuel tank give the reading to the powertrain control module.

 

That explains whats going on, my fuel cap on my tank has a one way valve that will allow air to be drawn into the tank so when I unplugged the vent it screwed up the system. I will try and find a cap with no vent at all.

Denny

 

are you talking about the the cap on your auxiliary tank!

 

Yes the aux tank not the main tank

Denny

 

I dont no the configuration of your system but if there no other vent on that tank, do not install a cap with no vent,when the tank get lower in fuel a vacuum will be create by itself, or you starve in fuel pressure or the tank shrink.you must install a tube on that aux tank and joint it to the main system on the truck.Be careful not every mecanic
anderstand well the evaporative system and how its work.

good lock

 

The tanks vent is tied to the trucks venting system, I have hooked the same tank to my 91 F250 and 2000 F350 the same way. The only that has changed is I unplugged the vent pipe.

Denny

 

In that case you can put a cap with no vent.

Alain

 

I sealed the vent hole with silicon for now to see if it works

Denny

 

I guess I circumvented that issue while being unaware of it.

I have a 12 volt shut off valve in line with the pump that draws the fuel from the aux. So when I turn off the switch the line is closed by the valve also - did that to insure no siphoning.

I vented the aux via a hose and filter down thru the truck bed and to the atmosphere. The aux tank has a roll over valve in it also.

 

This may be what I end up doing but first I'm tying the gas cap and then check all the fitting and where the fuel level sending unit goes into the tank. I'm also using a shut off solenoid in line with the pump.

Denny

 

Does anyone know where the canister is located, I looked everywhere and can't find it.

Denny