Land Rover Repair: losses power, worse the warmer it gets, security controller, operation temp

Question
Hey John,
I have a problem, the warmer my engine gets, the lower the RPMS will go. I have a 1998 disco 4.0 with 116,000 miles. When the engine is cold, it runs fine, but the warmer it gets the engine starts to bogg down and hold back by the time it is at full operation temp, it will barely rev up. I have a new fuel filter, and the fuel pressure stays constant from the time it is running great up to the time it won't hardly go. I read your answer to another disco owner's problem that the fuel pressure should be around 40 psi or so, mine is at around 30 psi idling and 34-38 under load. I'm not sure what it should be because the shop manual doesn't give the specs in PSI. This problem started all of a sudden one day. I had been driving and the engine was at full temp, with no problems, then like you hit a switch, the power just seemed to go away. I limped back home and since then, I have the problem that I described above. I have no check engine light, and no codes are set, but the converters get red hot. I have had the back pressure checked as well and there seems to be no restrictions in the exhaust. Any Ideas??
thanks,
Casey

Answer
Something is wrong with this story.

If the converters get red hot, that means one of two things:  1) the system is plugged up or 2) the engine is running way too rich or has ignition misfire

Now, if the check engine light is not on, given the above, either 1) the light does not work, 2) the system has been tampered with in some way, or 3) there is a problem with the GEM engine controller.

I suggest finding a shop that can swap the ECU and look at the live data from the engine.  You will need a LR specialist for this as they'll need to sync the GEMS unit and the security controller to get the truck to start with the different engien controller.