if you can find another EST Computer (inside the left kick panel under the glovebox) 
this is another SIMPLE swap to test. literally would take 10mins to swap over without mucking around with timing a dissy etc. 

they definitely do have issues (many EST dissy setups were converted to XE dizzy type  for this reason) 

just another option  (if you fit an XE dissy, or 1984/1985 XF **Leaded XF) and want to keep the current leads/dizzy cap, you need to get a 1984/1985 XF ROTOR BUTTON in the dizzy (the shaft size is different to the EST/TFi dissy of the unleaded models, so the rotor button cant be used.

there's probably a thread on it, but all you need to do (other than re time the dizzy due to removal) to install the XE dissy, is run the 2 wires to the coil (red for + green for - ) and unplug the EST computer.. and it will run as long as it's also in good condition. 


***side note***
I did this and left the EST computer plugged in, and it worked for years until suddenly it didnt. i can't remember what the symptom was, but the fix was unplugging the EST computer in the kick panel.. something was playing up in it, i think it was causing it not to rev much, would idle and not rev to 4000rpm etc.   

tried another new coil (C176) car ran fine for 5 mins then just stopped again and wouldnt restart, seems to be taking less time from when its running to when it cuts out.   going to have to take the dizzy out next and get that checked as mentioned above by Sparky_Dave ,..... running out of things it could be  

yeah i dont get it either

that's odd.
i have had a brand new coil no good out of the box about 30yrs ago.. bought one for the reco engine in My commodore at the time, ended up putting the original back on. 

annoying problems,   

update: i put a new coil on it (C176) and it ran very rough missing and carrying on (yes i double checked it was wired correctly same as old one) and the car cut off within a few minutes of idling, tried starting it was very hard to start and when it did was still running rough missing etc. I put the old coil back on it and runs smooth like it always has but it i wll cutout eventually after driving it for a while.So for some reason it didnt like the new coil. i checked the new coil with multimeter and it was within specs and so was the old original made in Australia one one.   I checked the dizzy for the centre carbon contact and it looked fine,i checked the wiring in and out of the fuse mentioned above and all looked good. i cleaned the contact faces on the main earth strap maybe that will help, if not i am running out of easier things to try and guess i will have to pull the dizzy out    

Cheers Bear👍. Yeah I knew about the winged sump on the phase 4's. Was just thinking maybe I should get a cooler for the Cleveland in my LTD to keep the oil cool was just a thought.

That's one of the main fusible links One supplies 12v at the EST diagnostic/base timing mode connectors near the brake booster The other, supplies power to the fuse box

thanks for the replies, gives me a few things to try, the coil is pretty hot,(almost too hot to hold) when it happens but i thought maybe thats normal given where its located, might try a new coil first as thats probably the cheapest and easiest. i did check it with a multimeter and was within range but given it happens only now and then i was thinking you could test it ten times and be ok then test it again and be bad so easier to just put a new coil on it for $50 odd .   I will check that wiring connection too, if that doesnt fix it i will have to look at the dizzy, i did take the dist. cap off and all looked good there   thanks for the replies

This happened to my own XF on a regular basis, very unnerving particularly while on the freeway.   I had auto electricians test the spark and approved it until it happened coming back from the sparky, fitted new coils was good for a while but then continued to do it.   Found the EST was good, dizzy good (apart from) damage being done everytime the thing backfired.   Turns out it was a loose broken wire connector next to the 2 main relays next to the battery which would cause the stall shortly after driving it.     Fixed and hasn't done it since (except because of the violent backfires from previous, I've needed to replace the dizzy gear wheel twice due to using secondhand replacements.  Crow cams supplied a new one plus a spare I'll probably never need to use.)         BTW, moved my new coil to the LH suspension tower away from the heat.    

From the description, it's most likely an ignition problem Specifically, a failing hall effect sensor inside the distributor   Luckily, those hall effect sensors can be purchased new The distributor has to come out, and be disassembled though   Example - https://www.ebay.com.au/itm/236524819457 (however E-series hall effect plates, have the hall sensor clocked differently)   You'd need one of these, instead - https://www.ebay.com.au/itm/277224475917