Operation and maintenance manual

Troubleshooting Symptoms Charts QSB4.5 and QSB6.7
Page TS-42 Section TS - Troubleshooting Symptoms
Engine Will Not Reach Rated Speed (RPM)
Cause Correction
STEP 1
Electronic fault codes are active
.............
For instructions on how to read active fault codes,
refer to Section 1. If fault codes are active, contact
a Cummins Authorized Repair Facility.
OK
Go To Next Step
STEP 2
Vehicle speed is too low for adequate cooling with
high engine load
.............
Reduce the engine load. Increase the engine (fan)
rpm by downshifting.
OK
Go To Next Step
STEP 3
Tachometer is not calibrated or is malfunctioning
.............
Compare the tachometer reading with a handheld
tachometer or an electronic service tool reading.
Calibrate or replace the tachometer as necessary.
Refer to the OEM service manual.
OK
Go To Next Step
STEP 4
Air-fuel tube leaking, wastegate diaphragm
ruptured, or wastegate plumbing damaged
.............
Tighten the fittings, repair plumbing, replace
wastegate diaphragm. Refer to the OEM service
manual or an Authorized Cummins Repair Facility.
OK
Go To Next Step
STEP 5
Charge air cooler restricted (if equipped)
.............
Inspect the air cooler for internal and external
restrictions. Replace the restricted cooler if
necessary. Refer to the OEM service manual.
OK
Go To Next Step
STEP 6
Fuel supply is not adequate
.............
Check the flow through the filter to locate the
source of the restriction. Refer to the OEM service
manual.
OK
Go To Next Step
STEP 7
Exhaust back pressure too high
.............
Measure and correct if above specification. Refer
to an Authorized Cummins Repair Facility.
OK
Go To Next Step
STEP 8
Fuel lift pump is malfunctioning
.............
Check the fuel lift pump for correct operation.
Check the pump output pressure. Replace the fuel
lift pump if necessary. Refer to an Authorized
Cummins Repair Facility.
OK
Go To Next Step