14 - Boost Pressure Test

14. Boost Pressure Test






Purpose:
To determine if the engine can develop sufficient boost to obtain specific power.

Recommended Procedure:
Monitor NGS Tester PID MGP and RPM. After the engine is up to operating temperature, find an open section of road and select the best gear to achieve a 2500-3000 rpm acceleration. With the accelerator at WOT, note the highest boost reading while accelerating through the 2500-3000 rpm range. Boost will level out after 3000 rpm. This is best accomplished either climbing a hill or with the vehicle fully loaded.












Alternate Procedure:
Install a T (manufactured locally out of common fittings) into the Manifold Absolute Pressure (MAP) sensor line that comes from the intake manifold. Make sure the MAP sensor is hooked up for this test.

Connect a T to a 0-30 psi gauge that is temporarily installed in the cab. Route the hose so that it is not crimped and does not come in contact with any hot surface.

Possible Causes:
- MAP hose pinched or open
- Leaking intake, hoses or fittings
- Defective turbocharger
- Base engine failure

Added Causes for F-Series
- Plugged green wastegate hose or port in the charge air intake to the turbo
- Wastegate control solenoid not electrically but mechanically inoperative
- Wastegate actuator
- Wastegate valve
- Wastegate turbo
- Intercooler hoses leaking







A wastegated turbo is designed to reach maximum boost sooner then a conventional turbo, but overboosting will cause damage to the turbo. The PCM will control the boost pressure by duty cycle to the solenoid to maximize boosting performance. When pressure is supplied on the red hose going to the actuator (solenoid NOT energized) the valve will open, dumping boost. When low or no pressure is on the red hose going to the actuator (solenoid is being energized) the valve will stay closed.