Ignition Timing R Bortignon 1 What is Ignition

Ignition Timing R. Bortignon 1

What is Ignition Timing? • ignition timing determines when the spark occurs in relation to piston/crankshaft position • ignition timing is stated in degrees of crankshaft rotation Ø TDC = Top Dead Center Ø BTDC = Before Top Dead Center Ø ATDC = After Top Dead Center • ignition timing adjustment must be set correctly for best vehicle performance, fuel economy & lowest emission levels • ignition timing is not the same procedure as valve timing • on vehicles with distributors, ignition timing should be checked & readjusted during tune-ups & after the distributor has been removed & reinstalled from the engine • timing can only be adjusted on vehicles with distributors! Ø vehicles with DIS or direct ignition has the timing controlled by the computer and is not adjustable 2

How to Check & Adjust Ignition Timing • • • connect the timing light to the spark plug wire on cylinder #1 timing light flashes every time #1 spark plug fires timing specs can be located in the under-hood tune-up decal or in Mitchell/Alldata 3

Follow timing preparation procedures… • • this prepares the engine for ignition timing refer to the under-hood tune-up decal Ø engine at normal operating temperature Ø vacuum advance disconnected? Ø correct idle speed Ø computer controlled engines v disable computer’s influence on timing 4

Checking & Adjusting the Timing • clean & paint the timing scale & notch (with engine off) 5

Adjusting the Timing • slowly rotate the distributor while the engine is running until the marks are aligned • tighten distributor hold-down bolt then re-check timing 6