Driveability - General Information
Driveability is a term which in general describes vehicle performance on the road. Driveability problems for an
engine can be caused by several different factors. Some of the factors are engine related and some are not.
Before troubleshooting, it is important to determine the exact complaint and whether the engine has a real
driveability problem, or if it simply does not meet driver expectations. The ‘‘Driveability-Low Power Customer
Complaint Form’’ is a valuable list of questions that must be used to assist the service technician in determining
what type of driveability problem the vehicle is experiencing. The checklist must be completed before trouble-
shooting the problem. If an engine is performing to factory specifications but does not meet customer expectations,
it must be explained to the customer that nothing is wrong with the truck and why. The form can be found at the
end of this section.
The troubleshooting symptom charts have been set up to divide driveability problems into two different symptoms:
‘‘Engine Power Output Low’’ and ‘‘Engine Acceleration/Response Poor’’.
Low Power is a term that is used in the field to describe many different performance problems. In this manual,
however, Low Power is defined as follows: The inability of the engine to produce the power necessary to move the
vehicle at a speed that can be reasonably expected under the given conditions of load, grade, wind, and so on.
Low Power is usually caused by the lack of fuel flow which can be caused by any of the following factors:
— Incorrect Fuel Pump or Injector Calibration
— Lack of Full Travel of the Fuel Pump Throttle
— Plugged ASA
— Excessive Fuel Inlet, Intake, Exhaust or Drainline Restriction
— Loose Fuel Pump Suction Lines
Low Power is not the inability of the vehicle to accelerate satisfactorily from a stop or the bottom of a grade. Refer
to the troubleshooting tree, ‘‘Engine Power Output Low’’ for the proper procedures to locate and correct a Low
Power problem. The chart starts off with basic items ‘Basics’ which can cause low power. It then breaks off into
application specific items ‘Application Specific‘ that can cause low power. All of the ‘Application Specific’ charts
end with a step called ‘Fuel or Air Delivery Problem’. This step leads toan engine performance check which requires
engine measurements. The last section of this chart is titled ‘Performance Measurement’ which leads the trouble-
shooter through the causes and corrections based on the outcome of the performance check.
Basics
Industrial
Elec. Dr.
Mech. Dr.
Genset Marine Automotive
Automotive
CELECT
Performance
Measurements
Poor Acceleration/Response is described in this manual as the inability of the vehicle to accelerate satisfactorily
from a stop or from the bottom of a grade. It can also be the lag in acceleration during an attempt to pass or overtake
anothervehicle atconditions less than ratedspeed and load. Poor Acceleration/Response is difficult totroubleshoot
since it can be caused by factors such as:
— Engine/Pump Related Factors
— Driver Technique
— Improper Gearing
— Improper Engine Application
— Worn Clutch or Clutch Linkage
Troubleshooting Symptoms Charts SectionT-Troubleshooting
N14Page T-106
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