Error code: 21 Ignition primary signal

Thank you for your reply. I have done the compression test as you have asked.
The reading are: 125, 75,110, 0,125,170 psi from 1-6 cylinders respectively.
Has the timing belt slipped? Please reply

Hi Ken,

I didn't have enough time after the new year break, anyway I finished the skyline head installation last week. After the head removal we noticed the head gasket had been blown and couple of valves found leaking during the vacuum test. Head was repaired by a pro, the repair involved resurfacing, valve grinding and clearance setting. After completion of the head installation job the car started straightaway but the power was not enough when driving. The check engine light was on. ( Check engine light was appearing before the repair work also.) I checked the sparks. Two of the spark plugs (5 and 6) had no indication of firing. As all spark plugs are new and after finding the power and earth good in the wire harness, I suspected the coils. After replacing the coils with the new ones the power is back but the check engine light keeps coming on. All cylinders have 180 psi compression. Car is running perfectly.

The error code is 21 which is for "Ignition primary signal". Cleared the cord but reappears.

Now, Ken I have few questions on this matter. I feel uneasy without knowing the answers. As you are an expert I hope you will help me.

What could be the cause for the blown gasket? Why were the valves leaking?

Which could have happened earlier, the coils going bad or the gasket getting blown?

Is the ignition module faulty?

Where is the location of this module?

I will be very grateful for your explanation.

Kind regards,

Raj

Coil on plug system. Replaced all coils with new one but the wire harness is not replaced. I think that the ECM controls the ignition and there is no ignition module.
So do you think the problem is with the coil wire harness?