the e38 ecu has oil temp sensor input so will only work if the sensor is fitted and wired in, oil temp sensor is tied in with the oil level sensor, also not sure why anyone would want fpcm in reality it doesn't do anything to help fuelling only benefit is they have fuel pressure sensor
only need do the injector/coil fuse for each bank they use the same fuse one for bank 1 other for bank 2, then dosnt matter what the fuel does as it wont ever fire the injectors, may not even cause a code as it dosnt fire or if it does soon as the fuse is back in it will see its fixed and clear
looking at the oil on the side of the sump internals looks by the color the oil has been hot and prob running out of oil too, was prob burning oil and never checked level and it got too low/hot and created the now issue
did u try the test in engineering mode settings ? if pointer sits right there then its fine, could even be either sender in the tank as when they play up it will read lower then actual
might need to clear something up ''purchased with knock in engine'' has this been running with the knock sounding (with hole in sump) or just mentioned as an issue on purchase and engine dosnt run ?
i ended up getting a set of these, also adjustable, they allow the engine to shake the car with the camshaft but take the annoying harmonics out of it
https://www.torquemaster.com.au/