1999 disco I with many issues solved. many new parts (magna flow cats, o2 sensors, etc, etc, etc). still have poor fuel economy (6-8 mpg) sometimes. while monitoring live data from obII scan tool, i noticed quite by chance that after vehicle idles for about 2 minutes, fueling goes to "open loop" and will not switch back to closed no matter how far driven. once key cycles back through off-on cycle goes back to closed loop, and will switch from closed to open to closed when running down road at minimal and changing throttle positions (which i assume is normal). additionally, i am seeing error codes related to max fuel trim values after about 100 miles of running. short term fuel trim seems to stay predominantly maxed at +24.2%, long term at -24.2%. o2 sensors voltage values seem to fluctuate normally - but sometimes bank number 2 fuel trim numbers much different than bank 1. what should i infer from this?

additionally, i note that without idling (and i am assuming without constant open loop fueling) my last tank of fuel at highway speeds was in 12-13 mpg range.

have looked hard for vacuum leaks - even resorted to spraying starting fluid along intake's exterior to listen for changes in running pitch/rpm increase. seems to be sealed tight.

 

At 180K, my D1 did 16 mpg on the 50 mph drive from my offspring's college nearby. The GEMS control has specific conditions to switch from closed / open loop.

One of these is the engine coolant temp reaching a warmed up value in 90 seconds from a start of 20 degrees C.

Engine Coolant Temperature - Warm up time limit, [closed loop fuel] typically 90 seconds at 20oC start temperature


Your scanner should show the digital temp from the ECT, this is a separate sender from the heat gauge. If reading -40F, as an example, it could be disconnected. Gauge sensor on left in pix, one wire, ECT on right with square top. Pix shows how gauge and OBDII readings can be quite different. Sensor should show parking area ambient temp at cold start. If readings way off, consider an new sensor.


GEMS manual attached, more in depth explanation of voltage values from O2s, etc.


If running "cold" I guess it could also be no thermostat or a stuck open one. Even when 32 F outside, should warm up at idle to 180 - 190F.

 

What codes are you getting? And are you sure you have the right oxygen sensors?

 

Codes 1187,1177, 1179 most recently. Also had odd quirk occur today. Flashers, or really both side turn signals triggered at once and would not cancel. I had to unhook battery - then when reconnected both turn signals were on simultaneously until they mysteriously turned off after an off to on key cycle. Any possibility this might somehow be related to other codes/ECM problems? I was told by a land rover parts supplier that ECM could retain "bad"data from period of time this truck was run with incompatible o2 sensors and that might be related to poor fuel economy and switch to open loop fueling. Any thoughts other than taking to land rover dealer service

 

The turn signals is either the inertia switch or the hood switch for the alarm, both are common.
Reset the inertia switch on the firewall, just press the button.
Then make sure the button on the drivers fender is pressed down all the way, you can just unplug that one.
Its common for the hood to bounce and trigger the flashers because that button pops up.
The flashers coming on has zero to do with any trouble codes.