Testing Spark Plug Wires

[Keith W.]

I thought I read somewhere with a timing light that it’s possible to test all spark plug wires. Is this accurate by moving the clamp from #1 wire when timing the engine to other wires?

[Owen L.]

I thought I read somewhere with a timing light that it’s possible to test all spark plug wires. Is this accurate by moving the clamp from #1 wire when timing the engine to other wires?

I've suggested that either here or on CF. Moving the pick-up "clamp" to each wire with the engine running, you can watch the flash for consistent firing. You're not using the timing light for anything other than it's ability to flash when electricity flows through the pick-up clamp. A missed flash is pretty easy to spot.

[Keith W.]

I've suggested that either here or on CF. Moving the pick-up "clamp" to each wire with the engine running, you can watch the flash for consistent firing. You're not using the timing light for anything other than it's ability to flash when electricity flows through the pick-up clamp. A missed flash is pretty easy to spot.

Thanks Owen! Much appreciated.

[David H.]

Keith

Voltage needed to "trigger" a timing light, less than voltage needed to fire a spark plug.

You might try tack welding an alligator clip to a spark plug. You can attach to any engine ground and test spark. I remove part of spark ground - makes center electrode to ground easier to see.

Dave

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[Duke W.]

Another test is resistance. OE type RFI wires should be no more than about 5K ohms per foot. On a small block the four long wires (1, 3, 2, 4) should be no more than about 15K and about 10K on the four short wires.

On big blocks there's not a great difference in length, so all should be in the same ballpark, and look for consistency of resistance for wires that are about the same length.

If you have other than the OE type RFI wires and don't know the resistance spec, look for resistance consistency among wires of approximately the same length.

Duke