The metal shield is for EMI reduction; it is a resistor. The failure of one or more of the resistor ends is a common cause of sporadic misfires. You may want to check the ballast resistors while you’re at it.

The ignition systems on these cars are particularly sensitive to the quality of the components. The original plug wires are very long-lived on these cars – this cannot be said of the aftermarket ones.

You can check your existing plug wires for the proper resistance. If you find one or more is not within spec, you can replace the resistor ends individually. (This is assuming that the wire insulation is still in good condition.)

Do not use aftermarket plug wires; even the Bosch ones have not been nearly as reliable as the OEM ones. Beru is the OEM manufacturer. If you’re going to keep this car for a long time, do not skimp on replacement wires.

Two more things. Do not think that you can use resistor type spark plugs as a substitution, it’s not going to work properly. Also, do not be tempted to use platinum plugs – they simply do not work well in that engine. Use the Bosch copper core plugs, preferably with the “O” suffix.


RTH