Mercury Optimax 115 Service Manual page 70

Symptom
3. Engine idle is rough
4. Engine idles fast (RPM
>700) or surges
5. Engine runs rough below
3000 rpm
6. Engine runs rough above
3000 rpm
90-855347R1 JANUARY 1999
DFI Troubleshooting Guide (continued)
Cause
3.1 Low air pressure in rail (less
than 79 2 psi while running)
3.2 Fouled spark plug
3.3 Failed direct injector
3.4 Failed fuel injector
3.5 Bad coil/weak spark
3.6 Flywheel key sheared
4.1 Broken fuel pressure regulator
or tracker diaphragm
4.2 Fuel leak
4.3 Tracker Valve spring missing
4.4 Improper set-up
5.1 Fouled spark plug
5.2 Low air pressure in rail
5.3 Throttle misadjusted
5.4 Bad coil/weak spark
5.5 TPS malfunction
6.1 Fouled spark plug
6.2 Speed Reduction
6.3 Low air pressure in rails
6.4 TPS malfunction
Action
See 1.2
Replace spark plug:
–If carbon bridges electrode gap
or if it is completely black.
–If it is not firing and is wet with
fuel.
Note: If spark plug is grey or com-
pletely black with aluminum specs,
this indicates a scuffed piston.
Refer to specifications for ohm
test.
Refer to specifications for ohm
test.
Refer to specifications for ohm
test.
Remove flywheel and inspect key.
Measure fuel pressure. Remove
and inspect diaphragms (a special
tool is required for assembly).
Check for fuel entering induction
manifold or air compressor inlet.
Fuel pump diaphragm leaking and/
or Vapor Separator flooding over.
Inspect tracker valve for proper as-
sembly.
Check throttle cable & cam roller
adjustment.
See 3.2
See 1.2
Check throttle cam setup on induc-
tion manifold. Inspect linkage and
roller.
If throttle plate stop screws have
been tampered with, contact Mer-
cury Marine Service Department
for correct adjustment procedures.
See 3.5
See 2.4
See 3.2
See 7
See 1.2
See 2.4
IGNITION
Page 2A-17