1986–1992 Toyota Supra
By Ray Delgado ✓ Certified Mechanic · Published Sep 24, 2026 · Updated Oct 14, 2026
Save $305 by doing it yourself! Shop cost: $344
Quick answer: Spark Plug Replacement on a 1986–1992 Toyota Supra is rated Moderate and takes about 1–2 hours. You'll need 7 tools for this job, and parts cost about $39. This guide walks you through the full job step by step, including the mistakes to avoid.
| Part Name | Part Number | Price | Buy |
|---|---|---|---|
| 6 spark plugs for the 7M-GE (gapped 0.032 in / 0.8 mm) | — | $39.00 |
About prices: shown prices are typical retail averages and change frequently; cheaper alternatives may be available. Confirm the current price before buying.
💡 Pro tip: Order all parts at once to save on shipping
Follow these steps carefully
The 1986½–1992 Mk3 Supra used the 7M-GE or turbo 7M-GTE (1987–1992): both distributor-ignition, six plug wires, no coil packs — same procedure. Turbo's plug valley is tighter. Let the engine go cold.
Remove the plug cover: three nuts on studs, 10mm socket, lift straight off. Check its rubber gasket — replace if flattened or cracked; a leaking cover pools water around wires and causes misfires.
Tape-label each wire with its cylinder (1 front, 6 rear) before pulling anything — crossed wires kill firing order. Twist boots off by the boot, never the wire; 30-year-old wires separate from terminals if yanked. Replace cracked/original sets.
I've watched guys chase a phantom 'bad tune' for a whole weekend over two swapped wires. Tape and a marker are the cheapest tools in this job — label first, don't touch a wire until every one is numbered.
Blow compressed air down each plug well before loosening plugs — valley grit drops into the cylinder when a plug backs out. Flashlight each tube: standing oil means leaking valve-cover tube seals; replace them or the new plugs foul.
If I find oil standing in a plug well, I don't just mop it up — I know those are the valve-cover tube seals leaking, and I've had new plugs foul in a few thousand miles from ignoring them.
Back out each plug front to rear with a 5/8-inch (16mm) rubber-insert plug socket on a 6-inch extension, kept straight — plugs sit at an angle and side-loading cracks the ceramic. Stubborn ones yield to steady pressure.
Gap each plug against your emissions sticker or manual — never guess. Hand-thread several turns with just the extension; it must spin freely. Give the box-specified seating turn, typically a quarter to half turn — overtightening strips the aluminum head.
I gap every plug even when the box says pre-gapped — I've been burned too many times. And thread them in with the extension only; the instant you feel resistance, back out and start over.
Seat each boot until it clicks, checking labels — one crossed wire and the 7M barely runs. Refit the valley cover; snug the three 10mm nuts evenly, since overtightening cracks the ears. A stumble under load means a loose boot.
Test your repair before closing everything up. If something doesn't work right, double-check your steps.
⚠️ Common Mistakes to Avoid
1986–1992
1986–1992
2020–2024
2020–2024
2020–2024
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