So lets say you mounted the aux tank in the spare tire space and used the pump in that aux tank to transfer gas to the main tank when needed. If the aux tank held pressure/vacuum just like the main tank and the vents on both tanks were tied together...would there still be issues with the evaporative system? That may be too much of a simplification, or just totally wrong...but the basic idea I'm thinking is make it just seem like one large tank to the evaporative system. Would the volume difference really be an issue since the air volume in the tank is variable anyway as fuel is consumed? I know you would need to address other issues, like not over filling the main tank...I'm just wondering about the PCM issues Bob brought up. How does the PCM decide to flag those two problems? Is there a difference between how the 95-98 and 98+ Rangers would react since the pre-98 tanks don't have a fuel tank pressure sensor?
EDIT: Or would making the tanks switchable like is usually done be a better idea? Which configuration would offer the least number of problems?
1997 XLT Extended Cab 4.0 SOHC 2WD Manual