I have a 2018 Ford F150 XLT V6 3.3L. The past year or two my gas mileage has been dropping. I use to get close to 16mpg. Now I’m getting 13 to 14mpg. How do I test the fuel pressure. There is no test port? Since it’s a high pressure system I think it’s a little bit more complicated. Is there a way for me to use my FORScan program to check the fuel pressure?

 

The fuel system is in two parts.
A low feeding a high system through a check valve.
The low side pressure should show at Ignition on, then go to high pressure as the engine is running.
Expect to see around 60 psi then rising to 2000 to 3000 psi. on that PID.
.
Maybe a need to replace plugs.
Ox Sensors may need changing.
Might be the fuel.
Winter fuel formulation change is almost here and will lower mileage a bit in many locations where required.
Take a look at the Long Term Fuel Tables for both banks to see what shift there is in the positive direction. If more than 5% on a continuous basis, this may be the hint something is causing it.
Good luck.

 

When I bought the truck in 2022 I replaced the spark plugs and in summer of 2023 I replaced tue o2 sensors. The mileage doesn’t change between the summer and winter time.

 

Was there a check engine light/diagnostic code indicating that the O2 sensors had failed?

Do you have a Fuelly account or some other place where you log your gas mileage for each tank?

Is there a CEL or diagnostic code indicating a fuel pressure problem?

The first diagnostic question should always be "Is it actually a problem?" How has the problem been measured?

If there's actual empirical evidence of a problem, then the next question is "What variables affect the symptom I'm seeing?"

For fuel consumption, the variables that have the most effect, in order of greatest impact to least impact are:
- Driver's right foot
- Intentional changes to the mechanical condition of the truck (tires, payload, aero)
- Mechanical wear over time (brakes dragging, bearings failing, 4x4 staying engaged, etc.)
- Engine wear over time (spark plugs, air filter, crud buildup on throttle body/intake/ports, cats clogging, etc.)

Note that fuel pressure is not on that list. If you have poor fuel pressure, it will manifest in different ways that will be much more noticeable and urgent than a gradual decline in gas mileage over a couple of years.

Low and high pressure system fuel pressures are available to read using Forscan or maybe another type of OBD scan tool.