Misfire continues after I change the ignition coils and spark plugs

Also, just to add:

It's possible to have a breached head gasket without any coolant loss at all.

This page shows the different types of failure you could theoretically experience.

The Prius 1.8L is mostly known for the failure type shown as #6 on that page. That's compression to coolant, and would involve eventual coolant loss.

But every now and then we hear about one of the other kinds...

 

“Pressure” test is more typically called a compression test. There’s also leak-down test*, maybe better for determining head gasket integrity, one cylinder at a time, and where/how it’s leaking.

* Mentioned previously, post #7

 

I read it as a pressure test [of the cooling system] where you replace the radiator cap with a fitting which allows you to attach a gauge and a pump. Those in turn allow you to pressurize the system as if it were at full running temp.

All three of these tests can be useful in diagnosing different types of head gasket failures.

 

A borescope may not see the coolant drop when warm (metal expansion seals it) or even when cold (coolant pressure low). So the best practice is to pump up coolant pressure when cold, have pink coolant (not water) and use a high quality two camera borescope while recording.

The easier test is to look for “steam cleaned” piston(s). With gen3’s history of hg failures, the symptoms are often enough.

Ignore it and it’s new engine time. Which could be right now. One guy here tore his down three times before punting to another engine. If you have excessive oil consumption it’s engine time regardless.

Example Borescope Inspection
Car Care Nut HG Borescope at 7:40