Turbo Diagnosis - Isuzu L Series Manual

VII. Appendix – Miscellaneous Service Information
Turbocharger Boost Pressure Diagnosis
Listen below are suggested checks for determining the cause of lowered turbo boost
pressure (in the sequence they should be performed). To obtain maximum boost pressure,
the engine must be operated at rated RPM under a full load condition. Boost pressure is
measured with a mercury manometer. A pressure gauge may be substituted.
One of the following checks will uncover the reason for low boost pressure.
(Normal pressure is 11-16 psi.)
1. Check the throttle linkage for travel to full fuel position.
2. Measure the maximum no load engine RPM. Adjust if necessary.
3. Inspect the manifolds and turbo for cracks, loosened mounting bolts or leaking
gaskets.
4. Check the intake and exhaust systems for restriction, i.e., dirty air cleaner,
collapsed hose or crushed exhaust pipe.
5. Check the fuel system, i.e., air in the fuel, dirty fuel inlet screen (rock stopper),
dirty fuel filter, contaminated fuel or reduce fuel delivery to the injection pump.
6. Check the valve clearance adjustment.
7. Check the injection nozzles, i.e., popping pressure, spray pattern or
leakage.
8. While the injection nozzles are removed, check the compression pressure.
9. With the turbo mounted to the manifold inspect the following:
It is necessary to remove the intake and exhaust piping from the turbo.
a) The wastegate (if used) does not close completely.
b) Check the compressor wheel for damage.
c) Check the turbine side for heavy carbon deposits or damage.
d) Measure the wheel shaft end play and bearing clearance.
10. Have the injection pump tested by an authorized Zexel dealer for proper
calibration.
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L-Series Diesel 45