Hello gentlemen
I did my best to check any possible information here in forum, but now I'm literally stuck with no solution.
From time to time (like 1 out of 20 starts) starter on my X-type may not crank the engine, it just makes a loud noise. I lock the car with a key fob, unlock it and there is 50% chance that car will start. Sometimes I need to do this trick a couple of times to get engine running.


I had a couple of other issues with gremlins before, so I have made/replaced following:
1) replaced and flashed a new ecu (used)
2) replaced engine wire harness
3) mounted a new Varta 100A battery (had to remove plastic box for battery due to the size of this one)
4) starter was revised and rebuild

I got rid all of gremlins except this particular one, even after all mentioned fixes.

 

Double check your heavy battery cables, as it is a common issue that they can eventually develop corrosion beneath the wire insulation and then can't pass enough current efficiently.
Cables should not get hot when you have a heavy load on them

 

That's a tough one! Intermittent...
As Mark wrote above: Check for corrosion on all cable-ends.
Same for the wires/cables of the starter motor...

And you have replaced the engine wiring harness? That would have been time-extensive and expensive... Did that happen recently? Did you have a period without your new intermittent issue after installing the new harness? Is there any chance you would have forgotten one of the ground connections?

 

KyKa, when you say "loud noise", would you describe it as more of a very fast hammer hitting a hard steel plate (a ticking sound), or a squealing sound (like metal rubbing on metal)? The ticking sound is most likely battery cables. Granted, could be an infant failure of the starter too. But, if I had to bet, it is more likely the battery cable(s). If you have a squeal going on, then I would be saying to find a time when the starter is not engaging, pull the starter and check the teeth on the flywheel. It is possible you have a few missing teeth and this is causing a spot where the starter can not grab the teeth adequately to roll the engine.

 

The thought verbalized by Thermo above also crossed my mind; "...check the teeth on the flywheel. It is possible you have a few missing teeth...".
But I did not mention this, as I read your comment "I lock the car with a key fob, unlock it and there is 50% chance that car will start."
I just figured that I can't see, how the sprocket of the starter motor would be stuck in the section of the flywheel with the buggered teeth, and then after locking and unlocking it, the flywheel would have moved... ...but everything is possible, I guess...

Note aside:
I just cleaned and polished the flywheel of my van yesterday... gash, that is heavy, and accordingly solid. (I am currently fixing oil leaks there and replacing the clutch plate, and I will soon be doing the same on my X-Type, as there are also oil leaks, and I assume that the REAR crankshaft seal is partially to blame on the van and possibly fully to blame on the X-Type...).