Chart R5: Hard Start - Mercury MerCruiser Service Manual

Step Diagnostic Process
Complete a compression test on the
7 engine.
Was a problem found?
NOTE: The crankshaft position sensor (CPS) is an exception. It will not set a fault if it fails completely.

Chart R5: Hard Start

This procedure is intended to diagnose a PCM 112 mechanical shift engine that readily rotates the crankshaft, but takes a long
time to start. You are here because you answered yes to step 5 of the diagnostic roadmap.
Step Diagnostic Process
Did you complete the Visual/
1
Physical Check?
Use the CDS G3 service tool to check
2 for faults.
Are there any faults?
Check for bad fuel or problems with
3 the fuel filters.
Was a problem found?
Check for adequate spark at all of the
4 spark plugs.
Was adequate spark present?
Check the fuel pressure at the fuel rail.
Was the fuel pressure within
5
specification when the pump was
operating?
6
Is a scan tool being used?
Check for an ECT sensor shifted in
value.
With the engine completely cool,
measure the resistance of the ECT
7 sensor.
Compare the approximate temperature
of the ECT sensor to an accurate
reading of ambient air temperature.
Are the readings similar?
Check for an ECT sensor shifted in
value.
Using the scan tool with the engine
completely cool, compare the ECT
8
sensor temperature with an accurate
reading of ambient air temperature.
Are the temperatures within 5.5° C
(10° F) of each other?
90-8M0099748 eng DECEMBER 2015
Details
Refer to Section 3C ‑
Compression Gauge
Testing.
Details
–
If a sensor has failed, it will
normally set a fault in the PCM.
For the CPS, see the note,
following.
Check for contaminated fuel.
Check fuel filters and the
water‑separating fuel filter.
Try starting the engine with a
portable tank of known good
fuel.
Check for poor fuel quality and
improper octane rating.
–
Refer to Section 5A ‑ Fuel
Pressure Gauge Setup and
Use.
–
Refer to PCM 112–Section 3A
‑Component testing.
–
© 2016 Mercury Marine
Yes
Locate and repair the
problem. Retest the system.
Yes
Perform the Visual/
Go to step 2.
Troubleshoot the
faults. Refer to the
PCM 112 Service
Manual.
Use known good fuel.
Replace fuel filters.
Go to step 5.
Go to step 6.
Go to step 8.
Go to step 10.
Go to step 9.
Troubleshooting
No
Contact Mercury
Product Support.
No
Physical Check.
Go to step 3.
Go to step 4.
Go to Chart T4.
Go to Chart T3.
Go to step 7.
Replace the ECT
sensor.
Retest the system.
Replace the ECT
sensor.
Retest system.
Page 1D-9