Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
High Altitude Compensation System: Operation: Diesel
At high altitudes (above 4000 ft.), the solenoid valve closes or engages and fuel pressure builds up between it and the pressure control valve. As soon as the pressure acting on both sides of the valve equalizes, the spring force closes the valve slightly. This causes less fuel to be returned to the pump inlet. Pump pressure increases which moves the injection timer piston and the roller cage turns in the opposite direction to the cam disc, causing the disc to move up onto the cage earlier than usual so that fuel injection takes place earlier.
At low altitudes (below 4000 ft.), the solenoid valve is open or disengaged. Fuel is returned to the pump inlet by means of 2 feedback channels; the control valve and solenoid valve, and a channel beneath the control valve.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.