TM 5-3895-346-14
ENGINE OVERHAUL
SHOP NOTES
FUEL SYSTEM
SHOP NOTES - TROUBLESHOOTING
SPECIFICATIONS - SERVICE TOOLS
SHOP NOTES
INJECTOR CALIBRATOR READINGS
Several factors affect the injector calibrator-output readings. The four
major items are:
1. Operator Errors: If the column of liquid in the vial is read at the top of the meniscus instead of at the
bottom, a variation of 1 or 2 points will result. Refer to Fig. 1.
2. Air In Lines: This can be caused by starting a test before the air is purged from the injector and lines, or from
an air leak on the vacuum side of the pump.
3. Counter Improperly Set: The counter should be set to divert the injector output at 1000 strokes, but must be
reset for 1200 strokes to check 35 and 40 cu. mm injectors. It is possible that in returning to the 1000 stroke
setting, an error could be made.
This should not be confused with counter overrun that will vary from 2 to 6 digits, depending upon internal
friction. The fuel diversion is accomplished electrically and will occur at 1000 strokes (if properly set) although
the counter may overrun several digits.
4. Test Oil: A special test oil is supplied with the calibrator and should always be used. If regular diesel fuel oil
(or any other liquid) is used, variations are usually noted because of the effect of the oil on the solenoid valve
and other parts.
Figure 1. Checking Fuel Output
The fuel oil introduced into the test oil when the fuel injector is placed in the calibrator for a calibration check
contaminates the test oil. Therefore, it is important that the test oil and test oil filter be changed every six
months, or sooner if required. In addition, other malfunctions such as a slipping drive belt, low level of test oil,
a clogged filter, a defective pump or leaking line connections could cause bad readings. A frequent check
should be made for any of these telltale conditions.
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