Impco HHI, Service Manual

Page: 119 / 485

119
Diagram 1
When using the DST program to clear a DTC, always select the “Clear All Faults” function to imme-
diately turn the MIL OFF after a successful repair (as shown in diagram 1 above).
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 mix-
ture 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 occur 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 example 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 di-
rectly 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
terminals as this can also be a source of intermittent problems cause by improper handling of these
connectors.