G643(E) Service Manual 244 Chapter 7. Basic Troubleshooting
Cuts Out, Misses
Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases,
sometimes above 1500 rpm. The exhaust has a steady spitting sound at idle or low speed.
PRELIMINARY CHECKS
Perform the visual checks as described at start of “ Basic Troubleshooting” chapter.
PROBABLE CAUSE CORRECTIVE ACTION
Fuel system
malfunction
Check fuel system specifically for plugged fuel filter, low pressure.
Check for contaminated fuel.
Check lock off intermittent connection.
Check dither valve operation.
Ignition system
malfunction
Check for spark on the suspected cylinder(s) using a shop oscilloscope or
spark tester or equivalent. If no spark, check for intermittent operation or
miss. If there is a spark, remove spark plug(s) in these cylinders and check
for cracks, wear, improper gap, burned electrodes, heavy deposits.
Check spark plug wires by connecting ohmmeter to ends of each wire in
question. If meter reads over 30,000 ohms, replace wire(s).
Visually inspect distributor cap, rotor, and wires for moisture, dust, cracks,
burns, etc. Spray cap and plug wires with fine water mist to check for shorts.
Check engine ground wire for looseness or corrosion.
Component malfunction
Check for electromagnetic interference (EMI). A missing condition can be
caused by EMI on the reference circuit. EMI can usually be detected by
monitoring engine rpm with Service Tool. A sudden increase in rpm with little
change in actual engine rpm indicates EMI is present. If problem exists,
check routing of secondary wires and check distributor ground circuit.
Check intake and exhaust manifolds for casting flash or gasket leaks.
Engine mechanical
Perform compression check on questionable cylinders. If compression is low,
repair as necessary.
Check base engine. Remove rocker covers and check for bent pushrods,
worn rocker arms, broken valve springs, worn camshaft lobes, and valve
timing. Repair as necessary.
Related MIL Faults:
EST faults
ETC Sticking fault
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