Cold Dr-12 - Ignition Timing Check

Connect a tachometer and timing light to the engine. Ground the carburetor switch. Start and run engine until normal operating temperature is reached. Raise engine speed to more than 1100 RPM. Disconnect and plug vacuum hose to the computer (2-Bbl. models).
Engine speed should be within specifications when setting timing. Adjust idle speed to 450-650 RPM (2-Bbl. models) or 550-750 RPM (4-Bbl. models). Basic timing should be within 2 degrees of specification shown on vehicle emission label. Adjust timing if necessary.

Remove jumper lead from carburetor ground switch. Disconnect and plug vacuum hose to the computer (4-Bbl. models). Connect a vacuum pump to the computer. Apply 16 in. Hg vacuum. Raise engine speed to 2000 RPM. Timing should be within 4 degrees of specification. See the SPARK ADVANCE SPECIFICATIONS table below.

SPARK ADVANCE SPECIFICATIONS ⁽¹⁾

Application

Computer No.

Advance Spark

5.2L (2-Bbl.)

4379484

46°BTDC

5.2L (2-Bbl.)

4379682

46°BTDC

5.2L (4-Bbl.)

4379226

38°BTDC

5.2L (4-Bbl.)

4379228

38°BTDC

⁽¹⁾	Specifications are +/- 4 degrees.

If spark advance is not within specifications, replace the computer. If spark advance is okay, return engine to idle. Disconnect vacuum pump from the computer. Connect a vacuum gauge to the computer vacuum supply hose. Gauge should read manifold vacuum. If vacuum reading is not okay, check and repair vacuum supply from carburetor. If vacuum reading is okay, proceed to COLD DR-13 below.