Cylinder 1 not firing on 2007 Mondeo XR5

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I just replaced the head gasket on my 2007 Mondeo XR5 and am having an issue with Cylinder 1 not firing.

Th engine light is NOT on.

Car idles OK, but if I disconnect and reconnect the coil lead on Cylinder 1 there is no change in performance.

If I disconnect any other coil performance deteriorates and then gets better when it is reconnected (as you wourl expect.

My ODB intermittently tells me that Cylinder 1 is failing with a P301 error code.

If I am driving, it feels like the cylinder is trying to kick in when I accelerate.

We've tested the spark, which looks strong and have swapped coils and sparkplugs with other cylinders.

We listened to each injector using a screwdriver as a stethescope and they all sound the same.

Any suggestions appreciated.