How do I diagnose a poor starter on a Mazda RX-7 FB?

To diagnose a starter issue on an FB RX-7, we first need to know exactly what the car is doing when you turn the key. Starter failures on these cars usually fall into one of three categories.

Here is the diagnostic breakdown for each scenario.

1. You hear a single "click" but the engine doesn't crank

Difficulty: Easy to Moderate

This is the most common electrical issue. The click is the solenoid firing, but the starter motor isn't getting the juice to turn, or it's seized.

• The Hammer Trick: Tap the starter solenoid with a hammer or a jack handle while a helper turns the key ⁶. If it cranks, your solenoid contacts are sticking or worn out, and you need a new starter.
• Check Grounds and Connections: Rotaries are notoriously sensitive to bad grounds. Start at the negative battery post and follow the cable to the engine and chassis, cleaning off any corrosion ¹. Do the same for the main power wire at the starter.
• Voltage Drop Test: Check the voltage at the starter while cranking. At the 'S' terminal (the small trigger wire), you should see roughly the same voltage as your battery. At the 'B+' terminal (the heavy main power cable), you shouldn't see more than a 0.5 to 1-volt drop compared to battery voltage ¹. If voltage is dropping heavily, you have a bad cable, a bad ground, or an issue at the ignition switch.
• Jump the Solenoid: Safety Warning: Make sure the car is in neutral and the parking brake is set. You can bypass the car's wiring by jumping the positive battery post directly to the starter solenoid's start terminal ¹. If the starter works perfectly when jumped, your issue is in the wiring harness, relay, or ignition switch. If it still just clicks, the starter is dead ⁷.

2. You hear a fast spinning or "turbine" sound, but the engine doesn't turn

Difficulty: Moderate (Requires starter replacement)

If you turn the key and hear a high-pitched whirring sound, your starter motor is working, but the solenoid/bendix is failing to kick the starter gear out to mesh with the flywheel ⁶.

• There's no real fix for this other than removing the starter and either rebuilding it or replacing it. Bosch units are a common and reliable replacement for the FB ⁶.

3. The engine cranks, but very slowly

Difficulty: Easy

A rotary engine needs a starter spinning at about 225-250 RPM to reliably build compression and start ³. If it's dragging:

• Check the Battery: A weak battery is the primary culprit. Have it load-tested. Cold weather will severely impact a weak battery's cranking amps.
• Check for Internal Binding: Put a socket on the front main pulley and turn the engine over by hand to ensure it spins freely and you aren't fighting a mechanical bind or a locked-up accessory pulley ³.

What exactly is your FB doing when you turn the key? If you can give me the specific symptoms, we can narrow this down.