How long is your 1998 Cambria? How many slide-outs does it have?
I did a quick search on a 1998 Cambria. Does it have an aerodynamic cap above the Ford van? Or does it have the large boxy bed above? The few Cambria rigs I found were aerodynamic so your fuel economy should be a bit better.
Here are some ideas for improving your fuel economy.
- There is a mechanical issue, from a dirty air filter to something more in depth.
- On the open road, limit your cruising speed to between 60 and 63 mph.
- Weigh your rig during a trip, each axle separately, and then adjust the tire pressure for each axle according to the tire pressure chart for your particular tires. See the chart below as an example, not to be followed unless you have the same tires in the chart. Too much air will improve your fuel economy "slightly" but it will come at great cost to the quality of your ride.
There is one unique thing you can check for that can be done in seconds. Unsnap the forward end of the oval air intake tube, and rotate it upward to get it out of the way. The connection is located above the radiator. Look in the oval hole of the large black plastic portion that is above the radiator. If there is a plastic flap obstruction, the vehicle was serviced by someone who removed that large black plastic part (like when replacing the radiator for example) and forgot to fold the flap 180 degrees prior to installing it back on.
I believe it was during model year 2010, a recall was issued for this. A new Ford assembly line worker wasn't folding back the plastic flap during assembly, hence restricting air to the engine. The result was poor fuel economy and poor performance.