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INTERMITTENT PROBLEMS
Intermittent fuel system problems can prove to be the most challenging to repair. It is most important to
remember when looking to find the cause of these problems, to operate the system in the condition when
and where the problem occurs. An example of this would be, if the DST showed a lean fuel mixture at full
load, one of the first things to look at would be the fuel pressure. The fuel pressure would need to be
monitored while the machine is operating at full load, not at idle because the leaning effect does not oc-
cur at idle. Electrical problems should be treated the same way. One excellent tool for finding
intermittent electrical problems is the DST plot/log function. Set up the plot for the code that sets. An ex-
ample of this would be if an intermittent IAT code set, tag the IAT voltage and watch the plot. While
watching the plot, agitate the electrical wire connection at the sensor and ECM connector. The resolution
of the plot screen is such that you will be able to see any unstable voltages that you would otherwise not
see with a standard DVOM.
Caution should be used when pressure washing the under hood of any electrical system. Avoid direct
pressure spray on the system electrical connectors. They are splash proof, but if water is sprayed direct-
ly at the connector moisture can become trapped behind the connector seal and cause serious system
problems.
Extra care must be taken when probing electrical pins and terminals. Do not bend or spread these ter-
minals as this can also be a source of intermittent problems cause by improper handling of these
connectors.
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