1997 Mazda Protege Engine Temp. Gauge

I didn't see a wire in the middle of the cap. Only four plug wires. Attached is a picture of what my dist. cap looks like.

Your right there is a flat connector on top of the distributor, that has a wire harness connected to it. Is the coil inside the distributor?

Here's the strange thing. If you drive the car around town <50 mph, no problem. As soon as you go on the highway after about 15-30 minutes at highway speed, check engine light comes on, misfire #4. When I chaned engines I reused the intake manifold gasket. I have checked for leaks using carb cleaner but nothing showed up.

I know dumb rookie mistake. I did the engine myself. Would that cause the misfire problem?

Replaced the manifold gasket. Light stayed off for 24 hours then came back on. Still being triggered at highway speeds? Car runs great, idels at 750, timing is dead on.

I'm at a loss

Has new plugs and wires. I have not changed the ditributor cap or the rotor.

Will check the injector and get back.