Operation CHARM: Car repair manuals for everyone.
Manuals through 2025 now available!

Our trusted friends have launched a new website named LEMON, which has newer manuals. It also contains all the CHARM manuals.

LEMON is the spiritual successor to CHARM, I recommend you try it!

Link: lemon-manuals.la or lemon-manuals.org.ua

(Some people have issue connecting. LEMON is investigating. For now, use Firefox or change your DNS server)

Or, hide this message: temporarily or permanently

JB3 - Verify Scope Pattern 2



Spark Plug Firing Voltage Pattern:






- Is the average value of spark plug firing voltage greater than 20 KV with evenness of spark plug voltage 8 KV or less?

YES -- Problems affecting all cylinders: Wide spark plug gaps all cylinders (usually from worn electrodes due to high mileage). CHECK ignition coil wires for proper installation in coil. MEASURE resistance of ignition wires. REPLACE if greater than 7000 ohms per foot.

NO -- Go to JB4. JB4 - Verify Scope Pattern 3