Mercury 305 CID, Service Manual, Page: 668 / 967

ELECTRONIC FUEL INJECTION (MULTI-PORT AND THROTTLE BODY) - 5E-127 90-823225--1 1096
CUTS OUT AND MISSES
Definition: Steady pulsation or jerking that follows engine speed, usually more pronounced
as engine load increases.
PRELIMINARY CHECKS
Perform the important preliminary checks as described at the start of the “Troubleshooting Charts”
section.
CHECK IGNITION SYSTEM FOR:
1. Cylinder miss
a. Start engine, allow engine to stabilize, record RPM, then disconnect IAC motor. Stop engine,
ground one spark plug wire at a time. Restart engine and record RPM.
b. If there is an RPM drop on all cylinders, go to “Stalling, Rough, or Incorrect Idle” section. With
engine “OFF” reconnect IAC motor.
c. If there is no RPM drop on one or more cylinders, or excessive variation in RPM drop, check
for spark on the suspected cylinder(s).
d. If there is a spark, remove spark plug(s) in these cylinders and check for: Insulation cracks,
insulator cracks,wear, improper gap, burned electrodes, heavy deposits.
e. Spark plug wire resistance (should not exceed 30,000 ohms).
f. Faulty ignition coil.
g. With engine running, spray distributor cap and spark plug wires with a fine mist of water to
check for shorts.
CHECK FUEL SYSTEM FOR:
1. Contaminated or restricted water separating fuel filter.
2. Fuel pressure within specification. (Fuel pressure can be checked on fuel rail at the schrader
valve. Mechanical pump can be checked with a carburetor fuel pressure gauge downstream
from the pump prior to VST.
3. Faulty fuel injectors.