Visual Inspection; Performance Tests - Mitsubishi 4DQ3 Service Manual

When the engine is overhauled, it is advisable to conduct
the bench tests for checking the engine performance.
The purpose of bench tests is to make sure that each
major component has been properly serviced.

1. Visual inspection

Couple the engine to the dynamometer and inspect as
follows:
(1) Starting the engine
(a) Check the amounts of cooling water, lubricating
oil and fuel oil. Bleed air out of the fuel system.
(b) Place the starter switch in PREHEAT position to
preheat the combustion chambers. The glow plug
indicator lamp will glow red within 20 seconds. If
not, check the preheating system for condition.
(c) Place the starter switch in START position to
start the engine. Do not move the governor con­
trol lever to INCREASE position.
(d) After starting the engine, manipulate the gover­
nor control lever to run the engine at idling speed.
(2) After starting the engine
Check the following items and repair if necessary.
(a) Abnormal oil pressure and oil leakage.
(b) Abnormal noise.
If knocking is heard while water temperature is
low and the noise dies away as water temperature
rises, the engine is in good condition.
( c) Color of exhaust gases.
( d) Leakage of cooling water.
( e) Leakage of fuel oil.
(f) Fuel injection.
(3) Running-in the engine
While running-in the engine, check the following
items and repair if necessary.
(a) Oil pressure (3 - 4 kg/cm
(b) Temperature of cooling water (75 - 85
°
167 - 185
F).
(c) Temperature of lubricating oil (60 - 70
°
140 - 158 F in oil pan).
(d) Abnormal noise.
(e) Excessive blow-by, water leakage and oil leakage.
BENCH TEST
2 or 42.7 - 56.9 psi).
°
C or
°
C or
(f) The relationship between the load and running­
in period is as follows:
After running-in the engine, check the valve
clearance.
Engine speed
rpm
1000
1500
2000
2500

2. Performance tests

(1) Test condition
The engine must be equipped with the air cleaner
and alternator.
(2) Test items
• No-load maximum speed test (governor set)
• Fuel injection quantity test (control rack set)
• No-load minimum speed test (idling speed set)
(3) Test procedures (with dynamometer pointer in
OFF position)
(a) No-load maximum speed test (governor set)
While the temperatures of cooling water and oil
are still high after engine running-in, set the no­
load maximum speed.
(b) Fuel injection quantity test ( control rack set)
The fuel injection quantity can be set by means
of the governor fuel set lever. Loosening the set
screw at the top of the fuel set lever will increase
the fuel injection quantity, and vice versa.
( c) Move the control lever toward LOW SPEED posi­
tion and adjust the stop screw to set the idling
rpm to 650 to 700.
(d) Tune-up of engine output
The diesel engine output is based on the atmos­
pheric pressure and temperature. Therefore, the
output must be tuned up under standard condi­
tions. Multiply the output measured by the factor.
This factor can be computed by the following
equation.
Time min
Load PS
0
30
7.5 30
15 60
20
60