Looks decent enough so I would expect (hope, for your sake) it to go up quite a bit although no doubt someone will point out that a 98 car shouldn't have 2000 light units. That isn't a site I've seen before but I must admit the number of P38s, good and bad, that have been on carandclassic just recently have got a bit too much.

You'll get the Gearbox Fault message if the battery is getting tired and the voltage drops when cranking. If the battery is dying while driving, things will shut down in order of priority, so things like the AC and radio will stop working first. I had a bad connection between the alternator and battery so although the alternator was still working (so no warning messages) the power wasn't getting to the battery. It was some years ago (and Rob's suggestion reminded me of it) but first the EAS didn't rise, then radio went off, then HEVAC then ABS, then gearbox fault before there was finally not enough juice left to run the engine and it stopped. By then I was about 100 yards from home and managed to coast the rest of the way.....

Yes, lambda sensors and O2 sensors are the same thing. They look at the amount of Oxygen in the exhaust gases and from that can show if a bank is running rich or lean. With standard Zirconia sensors that you have, they give an output between 0v and 1V, 0V showing lean and 1V showing rich. However, they don't just sit in one place they will flip flop between the two extremes about once a second when everything is correct. If they are always hanging one way or the other, the engine ECU adjusts the injector timings slightly to correct the error, this is the short term fuel trims (sometimes shown on a scanner as STFT). This will normally be shown as a percentage moving between +5 and -5%. If the short term are always having to adjust one way or the other, the long term trims are adjusted slightly to bring teh short term trims back to either side of zero.

Pics have to be uploaded to a server somewhere and linked to from there. Most of us use Imgur.com, see https://rangerovers.pub/topic/1021-inserting-an-image-from-imgur.

You're right, bank 1 is RH as seen from the drivers seat (see https://www.roverparts.com/resources/videos/rover-engine-firing-order/ from 3:10). Lambda sensors will be shown by your scanner as B1S1 (bank 1 sensor 1) for the pre-cat and B1S2 (bank 1 sensor 2) for the post-cat. The same will go for bank 2 with B2S1 and B2S2. Post cat sensors are there to confirm the cats are working and shouldn't really change, they will just sit at around 0.5V all the time (as long as the cats are doing something). While looking for the bank numbering, I also found a few threads on various forums where people have the same P0171 code as you have which was traced to a leaking PCV hose. Not sure if this was on the supercharged or normally aspirated engine though.

Yes, that's where I connected mine and I've also used the ignition switched supply on the connector to install a couple of fag lighter sockets for plugging things in the boot in.

Cross bolted engines first appeared in the 4.2 version fitted to the long wheelbase Classic as a result of some research into producing a diesel version of the engine as it made the bottom end stronger. Other than that there is virtually no difference between the RRC and P38 blocks.

Not memorized, I just keep it open so I can quickly look stuff up. Ignition switched power to the HEVAC comes from a connector on the back of the BeCM that can be accessed by lifting the carpet in the RH rear passenger footwell (it's the only connector on the back so not difficult to find). That connector can overheat and lose power. On a pre-99 car that same feed also goes to the radio and the brake light switch and I was wondering if a loss of power to the brake light switch would cause an ABS error but it appears that on a 2000 they don't use the same feed (so that is that theory out of the window....). But, there is a feed from the ABS system to the HEVAC (no idea why) so it is possible that an ABS fault could shut down the HEVAC.

Behind the LH rear light there is a 4 way connector that would be used if you had twin towing sockets or are fitting one of the modern 13 way trailer sockets. That connector has permanent live, ignition switched live, reversing light feed and ground. The reversing light feed is the Green wire and ground is Black.

A bolt that goes into the main bearing cap from the side of the block. If you look at a P38 engine you will see them just above the bottom of the block where it meets the sump. It is easily possible to use a P38 block with the front cover and distributor for an RRC engine, numerous people have built an engine with a 4.6 P38 block to use them in an RRC by doing this.

By convention, bank 1 is normally the LH bank as seen from the driver's seat, so if you mean RH as looking at it from the front, you are correct. If you use your diagnostics to look at the live data from the O2 (lambda) sensors, the only ones you are interested in are the pre-cat ones. With the engine running normally they should flip flop between 0V and 1V. If they hang at either end, then either something is causing them to hang or the sensor is dead. Compare the readings you get from the bank 2 pre-cat sensors and see if there is a difference. If it is something else causing the problem, the ECU will adjust the short term fuel trims to compensate.

I would suspect your engine uses platinum spark plugs which normally have a change interval of something like 40-50,000 miles but if you don't know how long they have been in there, it's worth changing them anyway.

It is primarily inhabited by P38 owners but we do have a few with later models. The difference between this forum and a lot of the others is that most of us have been working on cars for years so the cause of a specific fault with one model of car is going to be much the same with something else.

Does it have the cross bolts on the mains? That is the main difference between the RRC and P38 engines even though they are both 3.9 litre (3950cc for both the RRC 3.9 and 4.0 litre P38).

I don't but as plod didn't specify cruise when they ordered my car, I haven't got it. However, on other cars I've found that it actually makes the economy worse as it will try to maintain the speed when going up an incline rather than keeping the throttle opening the same and allowing the speed to drop a little.

As he is fitting a later cluster to an early car, the engine type will be correct in the BeCM. Changing it from GEMS to Thor may correct the temperature gauge but there's no telling what other things would be changed. I think the main differences are going to be in the cluster pcb, in much the same way that the tacho will read differently if a diesel cluster is fitted to a petrol car or vice versa. The petrol ECU sends 4 pulses per rev while the diesel sends 3 and the correct reading is calculated by the instrument cluster itself.

You'll need to add an extra ground too. The early GEMS had a single wire to the gauge sender with the ground through the body (later GEMS have a different sender with two pins so has a ground wire to it), the Thor one has a 4 pin connection, two signal and two ground wires.

I did 800 miles at a steady 75-80 mph on Saturday and my trip says 22.3mpg......

But I was running on LPG so it's all pretty much irrelevant.

I would have gone about it a different way. Retain your existing main PCB and satellite board with the message centre on it but swap the actual gauges with their faces. That way, any differences between sensor voltages, will still drive the gauges to the same place. GEMS uses two temperature sensors, one for the ECU and one for the gauge but Thor has a single one containing two separate senders so it is quite possible the temperature/resistance outputs are different.

If it was a fuel pressure problem it would affect all cylinders equally so that would seem to rule that out. I'm assuming there is only one MAF sensor on your engine and not one per bank, so again that rules that out. That leaves the lambda sensors as there will be one, or possibly two, per bank. Can your scanner do live data? In which case log, if it can, or watch the outputs from the lambda sensors. They should flip flop between 0 and 1V about once a second. If either hangs at one end or the other, that is likely the problem. In saying that, the sensor gives 0V when lean and 1V when rich, so with a dead sensor giving a permanent 0V, the ECU would interpret that as lean so richen rather than lean off the mixture on that bank.

Does the diesel have a crank position sensor? On a V8 when they start to fail they do it when hot but will start working again once left to cool down. If it does and it is accessible, when it stops, spray it with cold water to cool it down. If it restarts immediately then that is likely the problem.

Is it the hose or the clip? I've found that the constant tension spring clips are fine if they are fitted exactly perpendicular to the stub. If they are on at a slight angle they will leak. Easily done considering what a pain it is to get to them.

I normally use the Diagnostic function and move them from 0 to 100%. You can hear them operating and see what the feedback pot is reporting. It will often go to 105% (which is a good trick if you can do it) but you'll be able to see if you are getting full travel and the correct feedback.