Mk8 Transit Not Starting

[TransitWilf]

Hi Guys, First post on here and need some help.

I have a 65 plate Mk8 transit and it has a starting / running fault.
When you turn the key the starter motor turns for a split second then cuts out, turns the cuts out on a repeat cycle with no start. It will very intermittently start as it should (say 1 in a 100 attempts) and will then drive as normal but eventually brake down killing the engine randomly with no restart. This can happen after driving a few miles or after a hundred.
Its been to 2x different garages and both have drawn a blank. Also been looked at by a recovery mechanic when it had to be recovered to the garage first time it happened.
The starter motor has been replaced, there are no fault codes or warning lights, batterys are good, it makes no difference if you try to jump start off another vehicle, ECU been replaced this week and the fault is still present. All wiring has been visually inspected, relays checked and fuses checked.
Fords answer is part exchange the van which isn't really helpful especially on a van that not that old and only done 50K miles.
Anyone got any ideas?
The first garage that looked at it was a transit specialist who serviced and fixed Ambulances. He had all the kit to test everything and everything to him appeared normal. He diagnosed the Starter motor but that didnt fix it.

Thanks in advance
Wilf

[Altransit]

Has anyone tried replacing the ignition switch, or at least, testing it

[TransitWilf]

Thanks for the response.
The ignition switch has not been replaced but the first mechanic who looked at it (the transit specialist) had me turning the key while he checked things under the bonnet and did fault diagnosis with a volt meter in the area around the fuse / relay box. He said that all signals being sent to the engine to start were correct.

[JustJames]

one of the two batteries could be low, the starting battery or the running battery as ecu works from one the starter from the other
bad earth to the engine
clutch switch
wiring on the n/s chassis leg gets water in it
bad fuse - I've had a fuse that was corroded inside the plastic so check them all

best I can offer without seeing it

[loggyboy]

Did you ever solve this Wilf?