14 - Boost Pressure Test
14. Boost Pressure Test
Purpose:
To determine if the engine can develop sufficient boost to obtain specific power.
Recommended Procedure:
WARNING: ANY INSPECTION OF THE TURBOCHARGER MUST BE CARRIED OUT WITH THE ENGINE OFF AND THE TURBOCHARGER COMPRESSOR AND TURBINE WHEELS STATIONARY. THE TURBOCHARGER AND COMPONENTS MAY BE HOT. THE COMPRESSOR AND TURBINE WHEELS ARE SHARP AND SPIN AT HIGH SPEED. FAILURE TO FOLLOW THESE INSTRUCTIONS MAY RESULT IN PERSONAL INJURY OR DEATH.
1. Carry out the key on engine running (KOER) self-test to check the exhaust backpressure (EBP) system operation.
2. Monitor the MGP and RPM PIDs. After the engine is at operating temperature, find an open section of road and select the best gear to achieve a 2,500 - 3,000 RPM acceleration. With the accelerator at WOT, record the highest boost pressure reading while accelerating through the 2,500 - 3,000 RPM range. The boost pressure will level out after 3,000 RPM. This is best accomplished either climbing a hill or with the vehicle fully loaded. The boost pressure specifications are:
- F-Series/Excursion - 16 PSI minimum
- E-Series - 13 PSI minimum
If the boost pressure is less than the minimum specification, go to step
3. Check the intake and exhaust systems for restrictions, leaks, and damage. Refer to the appropriate Workshop Manual section to diagnose the low or no power concern. Check for low fuel delivery (Fuel Pressure Test), MAP hose restrictions, and worn engine components (Crankcase Pressure Test).
4. Visually inspect the turbocharger as follows:
a. CAUTION: If damage to the compressor wheel is present, the intake air system should be cleaned and inspected for foreign objects, poor maintenance, broken components, or improper installation.
Inspect the turbocharger compressor and turbine wheels for damage.
b. Note: The turbocharger shaft spins on floating bearings that require lubricating oil to provide proper running clearance.
Inspect for any evidence of wheel-to-housing contact; witness marks on the housing or rolled edges on the wheel.
c. Check the compressor and turbine wheels to verify they spin freely. The wheels should not contact the housing.
If the compressor and turbine wheels do not contact the housing, the blades are not damaged, and the shaft and wheels spin freely, the turbocharger is OK. If any of these 3 conditions are present, install a new turbocharger. Refer to Fuel Charging and Controls Turbocharger.
Alternate Procedure:
1.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.
2.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
- Damaged turbocharger
- Base engine
Added Causes for F-Series
- Wastegate hose or port in the charge air intake to the turbo restricted
- 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.