IGNITION
90-855347R1 JANUARY 1999 Page 2A-17
DFI Troubleshooting Guide (continued)
Symptom Cause Action
3. Engine idle is rough 3.1 Low air pressure in rail (less
than 79 ± 2 psi while running)
See 1.2
3.2 Fouled spark plug 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.
3.3 Failed direct injector Refer to specifications for ohm
test.
3.4 Failed fuel injector Refer to specifications for ohm
test.
3.5 Bad coil/weak spark Refer to specifications for ohm
test.
3.6 Flywheel key sheared Remove flywheel and inspect key.
4. Engine idles fast (RPM
>700) or surges
4.1 Broken fuel pressure regulator
or tracker diaphragm
Measure fuel pressure. Remove
and inspect diaphragms (a special
tool is required for assembly).
4.2 Fuel leak Check for fuel entering induction
manifold or air compressor inlet.
Fuel pump diaphragm leaking and/
or Vapor Separator flooding over.
4.3 Tracker Valve spring missing Inspect tracker valve for proper as-
sembly.
4.4 Improper set-up Check throttle cable & cam roller
adjustment.
5. Engine runs rough below
3000 rpm
5.1 Fouled spark plug See 3.2
5.2 Low air pressure in rail See 1.2
5.3 Throttle misadjusted 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.
5.4 Bad coil/weak spark See 3.5
5.5 TPS malfunction See 2.4
6. Engine runs rough above
3000 rpm
6.1 Fouled spark plug See 3.2
6.2 Speed Reduction See 7
6.3 Low air pressure in rails See 1.2
6.4 TPS malfunction See 2.4
To Next Page
Loading...
Need help?
General
