Q: The van cannot accelerate . 1986 VW Vanagon

Hi there - your thinking is good! Fuel supply can certainly prevent full engine performance. Checking fuel pressure, including while running and under load, is a good indicator. Make sure the fuel filter is not clogged, the fuel pressure regulator is maintaining proper pressure, and the injectors are not clogged or dirty. Don’t forget ignition however, bad plugs can kill performance as well, and are quickly and inexpensively changed. I recommend an loss of performance inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, and give you an accurate assessment of damage and cost estimate for repairs.