Connect a vacuum gauge to distributor main diaphragm hose and another vacuum gauge to BVSV port leading to carburetor. If equipped with high altitude compensation system (HAC), disconnect lower vacuum hose of HAC valve and connect it to intake manifold.
Check that coolant temperature is below 122°F (50°C). Start engine. Check that both gauges indicate zero. Warm up engine to normal operating temperature. Check that BVSV vacuum gauge indicates high vacuum.
On Federal models, pinch hose between vacuum pipe and vacuum transmitting valve (VTV). Increase engine speed to 2500 RPM and release hose.
Check that main diaphragm vacuum gauge indicates high vacuum within 1-5 seconds. Return engine to idle speed checking that main diaphragm vacuum gauge returns to zero.
On Calif. models, check that main diaphragm vacuum gauge fluctuates when the engine is accelerated and returned to idle. On all models, remove gauges and reconnect hoses.
Remove distributor cap and rotor. Apply vacuum to diaphragms checking that vacuum advancer moves. Reinstall rotor and cap. If system performed as described, testing is complete. If not, check individual components as necessary.

Fig 1: Tercel Spark Control System

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

System Testing: Tercel