- DEFINITION -
Diagnostic analysis involved certain checks that are
simple and easily performed. These checks usually
reveal the most frequently encountered causes of faulty
operation. The data obtained must be related to the
complaint. A failure may be due to a chain of conditions
that no one thought important enough to report. The
repair must include the discovery of the true cause of the
complaint and the corrective measures necessary to
correct the condition.
The key to successful diagnostic analysis is the mental
matching of the information of the condition with a
complete knowledge of how the engine and all its
components operate and their inter-relationship.
DIAGNOSTIC ANALYSIS PROCEDURES FOR
. . . OIL CONSUMPTION
When analyzing a lube oil consumption problem proceed
Visually inspect for external leaks and correct.
Check for air cleaner restriction, air induction
system leaks and excessive crankcase pressure
as specified in Section 5.
NOTE : On turbocharged engines, change oil filter
elements and inspect for turbocharger damage if
lube oil is drawn into the engine.
If items 1 and 2 are NOT the cause, continue analysis.
Verify the Problem -
Change the oil (using the recommended
temperature). See NOTE.
Determine initial oil consumption rate and
1000 miles/50 hours
5000 miles/250 hours
Record the amount of make up lube oil
added during the test period.
NOTE: Verify engine is equipped with proper dip-
stick. Wrong dipstick may result in erroneous
If oil consumption was excessive, determine the
cause of the problem.
Abnormally heavy loads pulled by the
vehicle. (Above the specified GVW).
Improper operation (i.e. allowing the engine
to lug in the incorrect gear range) resulting
in oil consumption.
Plugged air cleaner element causes high in-
take vacuum which will pull over oil through
(Clean element) .
piston rings are worn, oil can leak into the
Worn engine valve guides. (Clean, inspect
and replace if required).
Worn rings and/or bores due to dirt passing
. . . FUEL CONSUMPTION
When excessive fuel consumption is suspected,
verify the problem.
Compare the actual rate of consumption in
gallons per hour or miles per gallon against
normal expected fuel usage in subject
If excessive fuel consumption is confirmed
determine the cause of the problem.
Check entire fuel system (tank to injection pump)
Investigate possibility that engine is not in proper
diagnostic tests indicated in text.
Review drivers habits to be sure he is not
lugging or overspeeding engine.
Inspect engine per the "PERFORMANCE DATA
GUIDELINES" in the rear of each Engine
Section for the particular application.
Printed in United States of America