[spannerrash]

When I first started doing the compression tests it was only a bit of a "while I'm in there" afterthought. I was originally changing plugs and coils. So, plugs removed, coils removed and fuel pump relay removed. Both chain tensioners were still connected electrically.

I did remove the fuel pump relay first while the engine was still running in order to run the pressure out of the system. I can't remember exactly why but at this point I decided to scan the car once again for fault codes. I think I had the idea that checking fuel trims might help me find my misfire. Interestingly I had no faults prior to pulling the relay and multiple, seamingly unrelated faults afterwards.

I'm not sure what effect the removal of the relay has on the Ecu but it does seem like the Ecu doesn't like it and may in fact disable multiple other systems as a result.

I think at this point I need to reverse direction a little before disappearing any further down this rabbit hole. I'll put everything back together. Fit new plugs and coils (because I have them), run the engine up to temperature and then do a running compression test on cylinders 1 & 5. I will simply remove the plug, coil and disconnect the injector and run the engine on 7 cylinders for each test.

Hopefully this will eliminate the oil pressure and Ecu variables.

It will be a couple of days now before I get back to it as I have to work but I will let you know how I get on.

Actually, I think I'll connect an oil pressure gauge before I put it all back together as access is much easier. I'll then measure what oil pressure I generate at cranking speed with no plugs in.

Thanks for the help so far, much appreciated.