Page 34 - REPOWER REFERENCE GUIDE (2020)

Engine Failure Diagnosis

Connecting Rods
Water ingestion in a 4.3L engine resulted in a bent connecting rod and a failed exhaust manifold.

a a - Failed exhaust manifold
b - Bent connecting rod

b

a
68062
Cylinders
A 4.3L with a faulty carburetor providing excess fuel washed down the cylinders that failed due to lack of lubrication.

68065

Used Spark Plug Analysis

Spark plug condition can suggest a variety of possible engine malfunctions and indicate needed engine repairs. When the old
plugs are replaced, replace the entire set. Perform plug service only on those plugs suitable for additional service using the
following procedures:
1. Remove any oil deposits with solvent and dry plugs thoroughly.
2. Open the electrode gap wide enough to permit cleaning and filing.
3. Remove the combustion deposits from the firing end of the spark plug with a plug cleaner. Use compressed air to remove
abrasives.
4. File the electrode surfaces to restore clean, sharp edges. Remove filings with compressed air.
5. Reset the gap to specifications by bending only the side electrode with the proper tool.
6. Shake the plug and listen for a broken insulator tip "rattler" or any other evidence of loose internal parts. Change the spark
plug.
7. Measure the electrical resistance with a multimeter between the center electrode and the terminal post where the spark
plug wire attaches. Resistance should read between 1,500–10,000 ohms to prevent radio interference or an excessive
voltage drop that could result in low spark energy.

Page 3A-8 © 2019 Mercury Marine 90-8M0149179 eng NOVEMBER 2018