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Ignition TimingIgnition Timing

R. BortignonR. Bortignon

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What is Ignition Timing?What is Ignition Timing?

• ignition timing determines when the spark occurs in relation to ignition timing determines when the spark occurs in relation to piston/crankshaft positionpiston/crankshaft position

• ignition timing is stated in degrees of crankshaft rotationignition timing is stated in degrees of crankshaft rotation TDC = Top Dead CenterTDC = Top Dead Center BTDC = Before Top Dead CenterBTDC = Before Top Dead Center ATDC = After Top Dead CenterATDC = After Top Dead Center

• ignition timing adjustment must be set correctly for best vehicle ignition timing adjustment must be set correctly for best vehicle performance, fuel economy & lowest emission levelsperformance, fuel economy & lowest emission levels

• ignition timing is not the same procedure as valve timing ignition timing is not the same procedure as valve timing

• on vehicles with distributors, ignition timing should be checked & on vehicles with distributors, ignition timing should be checked & readjusted during tune-ups & after the distributor has been removed & readjusted during tune-ups & after the distributor has been removed & reinstalled from the enginereinstalled from the engine

• timing can only be adjusted on vehicles with distributors!timing can only be adjusted on vehicles with distributors! vehicles with DIS or direct ignition has the timing controlled by the vehicles with DIS or direct ignition has the timing controlled by the

computer and is not adjustablecomputer and is not adjustable

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How to Check & Adjust Ignition TimingHow to Check & Adjust Ignition Timing

• connect the timing light to the spark plug wire on cylinder #1connect the timing light to the spark plug wire on cylinder #1• timing light flashes every time #1 spark plug firestiming light flashes every time #1 spark plug fires• timing specs can be located in the under-hood tune-up decal or timing specs can be located in the under-hood tune-up decal or

in Mitchell/Alldatain Mitchell/Alldata

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Follow timing preparation procedures… Follow timing preparation procedures…

• this prepares the engine for ignition timingthis prepares the engine for ignition timing• refer to the under-hood tune-up decal refer to the under-hood tune-up decal

engine at normal operating temperatureengine at normal operating temperature vacuum advance disconnected?vacuum advance disconnected? correct idle speedcorrect idle speed computer controlled enginescomputer controlled engines

disable computer’s influence on timing disable computer’s influence on timing

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Checking & Adjusting the TimingChecking & Adjusting the Timing

• clean & paint the timing scale & notch (with engine off)clean & paint the timing scale & notch (with engine off)

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Adjusting the TimingAdjusting the Timing

• slowly rotate the distributor while the engine is running until slowly rotate the distributor while the engine is running until the marks are alignedthe marks are aligned

• tighten distributor hold-down bolt then re-check timingtighten distributor hold-down bolt then re-check timing