Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Transmission Controlled Spark: Operation
When transmission is shifted into 4th gear, the top gear switch on the transmission sends an electrical signal to the electromagnetic switching valve. This signal activates the switching valve, closing the vent passage and allowing full vacuum to the advance side of the distributor vacuum unit. In all other gear positions, the switching valve interrupts the vacuum normally directed to the vacuum advance unit and, at the same time, opens the vent passage so that vacuum can be released.
On 320, a thermo valve is added to this system to cut-off vacuum to the switching valve until engine coolant temperature reaches approximately 91°F (33°C).
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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.
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