Not a Jaguar, but my son's 2003 Nissan Pulsar/Almera. For some reason this car will not start. Was running fine until a couple of days ago. A few weeks earlier the car had failed to start and I diagnosed engine flooding. Cleaned the plugs and let the cylinders dry and it started fine. Now nothing. I have checked the valve clearances - all OK. Ignition - a big fat spark on all cylinders. Pulled the cam angle sensor and all seems good. Sprayed starting fluid - absolutely nothing - not even a cough.
Now I measured the compressions and they are way down. One cylinder is at 55psi, the others 75-90psi. I am at a loss to see why the car will not fire.
Question then is how low a compression does a modern car have to have before failing to start? After all, many pre- war engines would have a compression pressure in the 75psi range.

 

If your compression is too low U will have an issues starting it possible engine rings failure squirt some oil into the cylinders to boost the compression Dou it's not a fix more to troubleshoot

 

Mekon, from what you describe, I would be looking more at the timing of the car than compression. From the sounds of things, you have jumped a tooth or two and this is causing the valves to open too soon, killing the compression. This will also lead to hard start/no start conditions. Checking the timing should not be too bad as you simply have to remove a cover off the front of the engine to expose the timing marks. This is where having a manual on the engine will then tell you when your crankshaft is at XX position, the camshafts should be at YY position. Every engine is different. hence why I say to look in a book for the exact details. Also, you can determine which gear jumped as most cars have colored links (may be silver, may be dark, may be painted a color) that the timing marks should match up to. Again, the book will clarify how the colored links should appear

 

Yes timing, but it is also odd that you do not get some kind of pop with the starting fluid. I would check the condition of the spark at each plug.