What should the engine compression be

it varies between 100 psi and 150 psi across the four cylinders it varies between 100 psi and 150 psi across the four cylinders

That That

That is more variation than I like to see. Squirt some oil down the plug holes and measure again. If the pressure comes up, you may have a ring problem. If the pressure does not come up, then more likely it's valves. That is more variation than I like to see. Squirt some oil down the plug holes and measure again. If the pressure comes up, you may have a ring problem. If the pressure does not come up, then more likely it's valves.

I have returned the testing kit as I had only borrowed it. The car will not start except when towed. I have returned the testing kit as I had only borrowed it. The car will not start except when towed.

Compression isn't bad enough to be the cause of not starting. Compression isn't bad enough to be the cause of not starting.

Perhaps if you describe what happens when you attempt to start it in more detail, I might have more ideas. Perhaps if you describe what happens when you attempt to start it in more detail, I might have more ideas.

Engine turns over as normal but will not fire. Have checked fuel supply to injectors and all is ok. There is also good spark to the spark plugs. If I turn the engine over with the oil filler cap removed there is huge amounts of pressure and oil mist ejected through the oil filler. Engine turns over as normal but will not fire. Have checked fuel supply to injectors and all is ok. There is also good spark to the spark plugs. If I turn the engine over with the oil filler cap removed there is huge amounts of pressure and oil mist ejected through the oil filler.