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I currently am trying to find the cause of system too lean codes. PO0171 and PO0174
A little history
Purchased last year around April PO171 code showed up almost immediately. Cleaned Maf sensor, and put injector cleaner into fuel. That seamed to clear the code until September. Then the code started showing back up intermittently. Stored the truck until spring. Smoke tested intake over winter and found no leaks. When i started driving the truck a week ago both engine lean codes came back. Added injector cleaner to fuel that cleared the bank 2 (P0174) code but the bank 1 (P0171) comes back. There are no other engine codes shown. I started watching some live values while driving the fuel pressure fluctuates a bit at idle and while cruising at 2000 RPM. It falls to 41psi at times. and then quickly recovers. It does increase to about 55-60 psi under harder acceleration.
Today I removed the spark plugs and the front three spark plugs of bank1 (right side not sure what the cyl numbering is) are white compared to the rest which are a nice light brown.

Im trying to determine if the injectors are partly plugged or the fuel pump is possibly getting weak. It does not run rough or stumble when driving.
Scan tool is a IID tool
2008 Range Rover Supercharged Canadian vehicle

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Might be a stupid question, but how old are those plugs? And while you check 'live values', can you get access to the lamda data? I am very wary of both spark plugs and O2 sensors failing over time, perhaps not entirely but sufficient to give wrong readings which upset the fuel trims ...

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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.

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is the fuel pressure regulator manifold referenced? If so its normal that it will fluctuate around.

The aim is to maintain say 3bar across the injector. If the manifold is under 0.5bar of vacuum, the pressure in the rail will drop to 2.5bar. If there is 1 bar of boost in the manifold, the pressure at the rail will increase to 4 bar.

Returnless systems are not referenced like that, but the ECM can alter the fuel pump speed via PWM, so you may also get similar variations in pressure as the pump adjusts its speed to meet demand.

I'd be looking at the three odd cylinders and figuring out whats going on. Might be worth getting the injectors properly ultrasonically cleaned and tested? Its usually fairly cheap and can be a good thing on an older engine anyway. A free test would be to move the injector to another cylinder and see if the issue follows.

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fuel pressures should not fluctuate ever, you have about 2% fluctuation gap only. your pressures should be stable at all times and have a small decrease at idle only , about 3psi . if they are swinging then you have an unstable fuel supply , dose it surge or not wanting to rev at times
PS i do not work on super charged vehicles but i would expect the fuel pressure to be stable still even with a pressurized manifold.

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on a "traditional" vacuum referenced system the pressure will absolutely fluctuate, thats the whole point of the vacuum reference. On boosted cars the swings are even larger due to the boost reference. If there is 1bar of boost in your manifold, the fuel pressure rises by 1 bar to match it, to ensure injector flow rate remains the same.

My A4 runs a base pressure of 3 bar. however at idle its pulling 20 inhg of vacuum (about 0.6bar) and the rail pressure drops to around 2.5. At max boost it runs 1.5bar and the rail pressure rises to 4.5bar.

Early returnless systems, ran a fixed pressure, and the ECU compensates for the flow variations using a MAP sensor and a calibrated model of how the injector responds to the varying manifold conditions. Newer returnless systems have full PWM control over the pump and can adjust pressure at will as defined within their engine mapping.

Stick a pressure guage on your GEMS engine and you'll see it for yourself. Fuel pump running and engine off (no vacuum) will see about 2.5bar of fuel pressure. Once the engine starts and the vacuum acts on the regulator, it'll lower the pressure to around 2bar. Open the throttle and the pressure will rise back towards 2.5bar. Pull the vacuum line off the regulator and it will rise back towards 2.5bar. At wide open you'll see 2.5bar, and part load will vary between 2 and 2.5 depending on the exact levels of manifold vacuum.

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Sorry guys I have forgotten to check this forum after i realized I posted in the P38 section. Since I cant find an L322 section I assumed this forum was dedicated to P38. I will catch up tonight after work.

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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.

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Ok here goes
Leolito, No idea how old the plugs are, They dont look bad, no misfires or codes other than system lean bank1 (right side i think) which is where the white plugs are located. I can post a pic when i figure out how. I have o2 sensor reading for bank 1 only for some reason, not sure about voltage. It reads 96% for the first 20km or so then goes up to 98%. Interestingly though during accel or decell it does not read. Not sure if this helps will look into this more.

Gilbertd, 1 maf sensor right at the air filter, i think 4 o2 sensors (I think this is what you mean by lambda) before and after catalytic each side. More research to be done on this. Ditto on the fuel pressure. Im leaning toward poor/plugged injectors.

mad-as. Fuel pressure is controlled by ecu via a pwm signal, According to the manual it should fluctuate but be a relatively steady 45psi at idle.

Aragorn I need to get a pressure gauge and figure out where it gets hooked up. The injector rail is buried under the intercooler's. I am currently reading pressure from the scan tool, thats why i pulled the plugs. It is a returnless system.I believe the pressure regulator is vacuum referenced since there is a vacuum line running to the intake prior to the supercharger. The absolute pressure reading is approx 5-6psi at idle. I think this is a vacuum since with the engine off it reads 14.5(1bar) Fuel Pressure at hard acceleration is 50- 60psi (3.25-4bar?) Engine is a 4.2L supercharged Jaguar.

I did unload a whole can of WD40 all over the top of the engine looking for vacuum leaks and none were found. I will do a bit more this weekend with vacuum and hopefully a pressure gauge. For right now I have put 3 cans of fuel injector cleaner into the fuel, cleared the engine adaptive values and have not had the code return. Although I believe this is a temporary fix. I will pull the plugs again this weekend to see if there is a change. I expect the code will return at some point in the next few months. I am currently leaning towards poor/plugged injectors. Opinions and suggestions are welcome since I do not want to turn this into a parts cannon.

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a compression test on the lean side might be helpful or do all off them if you get suspect readings.

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I know nothing about the L322, but spark plugs are a cheap part, and you’re there anyway if you’re checking compression, especially as we don’t know how old they are.

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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.

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The plugs are iridium type. I had planned on changing them after i figure this out. I should have other ignition faults if they are the cause of the issue.
I need to get some new tools. My 1980s compression guage no longer holds pressure. And my IID scan tool does not give me all o2 sensors.
I will have to check the manual again, I thought bank1 was on the RH side from the drivers seat. It is also the furthest forward closest to the rad. Unfortunately the manual does not help with diagnostics only how to replace parts.
I dont think im going to get to far this weekend if my tools are no good.

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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.

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You guys know all the links! I havent found that one yet. I did look into the pcv valve. I removed it the diaphragm does move with suction. There is a small vent hole in the top that allows the diaphragm to move, tested that with wd 40 while running and nothing changed. Since it enters the manifold before the supercharger it should set off bank1 and bank2 codes. That's why I pulled the plugs to see if it was actually an issue or some stupid tiny vacuum leak somewhere affecting all 8 cyl. Since it seems to be only 3 cyl that would point to a local vacuum leak at the intake but it passed the wd40 sniff test.

I have borrowed a cheap obd2 reader that has the o2 readings, fuel trim readings, and lambda readings.
Thanks for the info on the o2 sensors. That was going to be one of my next questions. Can someone explain what the lambda is and what to look for. I have heard this term and it appears that i misunderstood it thinking it was another name for o2 sensors.

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Can I upload pics or do they have to be in some sort of online cloud thing?

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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.

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Ha, now this is bizarre. Its a good thing i have lots of hair to pull out.
My scan tool gives me a fuel pressure reading of 40 to 60 psi depending on how much lead my right foot contains. The unit I borrowed reads 10 psi less. Im not sure this means anything yet until i get an actual gauge on it.
Apparently my o2 sensors do not flip between 0 and 1 volt. They provide a constant variable readout between 0 and 1 volt, usually around 0.6-0.7 volts. Regardless both sides have very similar readings for upstream and downstream sensors. However the long term fuel trims are quite different. At idle they are quite similar but few decimals apart. But at 60mph cruise bank 1 reads 13.3% at 60mph cruise and bank 2 reads 8.8%.
I did read on another forum that plugs/coils or a bad cat could cause this. For all the work it takes, I might just swap the white plugs and coils to the other side and see if the fuel trim moves with them.
I was able to graph these and compare both banks, they stayed quite similar other than the fuel trims separating as I accelerate to cruise speed. Comparing cyl 1 and cyl 8 this also shows up in the injector timing with bank 1 having a longer firing time than Bank 2 as the speed increases.

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I've been away on holiday a few days so I'm late to see this thread but I've done plenty fuel system related work on Supercharged Rangerovers (I've converted plenty of them to LPG).

They have a returnless fuel system but fuel pressure is adjusted by electronics controlling the fuel pump... It could be termed 'on demand' fuel pressure. The engine management on them is very sensitive to vacuum leaks (including false air from a disconnected or failing cam cover breather, evap purge valve flowing when it should be closed, etc).

One unusual aspect of them - Say you've had an error code, then you reset the error code (which after some error codes will reset fuel trims)... If you then just start (after resetting fuel trims) and leave it idling the chances are you'll get fuel trim error codes. The way around that would be to clear error codes then not leave the car idling, instead start it up and immediately go for a drive.

With a basic scan tool you probably won't be able to manually reset fuel trims. But causing one of the more 'severe' error codes such as open circuit petrol injector then resetting error codes will reset fuel trims. I.e. If you want to reset fuel trims but don't have a scan tool with that function you can still reset fuel trims by disconnecting a fuel injector, let the system log the error code, then clearing the error code will reset fuel trims. But then don't forget to go for a drive immediately after starting the engine or you'll probably get a fuel trim error code anyway ;-)

A scan tool will show you fuel pressure... There's an electronic fuel pressure sensor built onto the fuel rail, there has to be one for the on-demand fuel pressure system to be able to read fuel pressure and control the fuel pump properly. Edit - Noticed you're getting 40>60psi, that seems about right to me, as memory serves my scan tools read between around 400 and 600kpa on most Supercharged Rangerovers depending on engine load.

The lambda sensors are wide band, any voltage reading from them is meaningless (a voltage reading from a wide band probe is meaningless without knowing how the 'pump' in the wide band probe is being controlled) but an OBD scan tool should be ale to tell you directly what mixture is, probably in terms of lambda (lambda of 1 means correct mixture, 0.995 slightly rich, 1.005 slightly lean). Mixture should stay close to lambda of 1 (which is 14.7:1) but go rich under boost conditions maybe down to around 0.8 at full engine output. The scan tool can tell you mixture because the engine ECU knows mixture, it contains a dedicated wide band lambda sensor control chip that 'homes in' on mixture by reading lambda voltage and knowing how much current (uA) it is applying to the 'pump' in the wide band probe.

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It appears you did not finish.
I am using a IID scan tool. There is enough stuff in this tool to get me into trouble. (I Cleared the trans adaptive values, took the better part of 2 months for the trany to relearn :-) )
Does resting the adaptive values reset the trims? I did that 2 weeks ago.
The lambda's are hovering around the 1.00 mark. I will pay more attention to them tomorrow?
I dont usually let it idle before driving unless trying to figure this out which is mostly after/during a drive cycle. The code takes usually takes 3-5 drive cycles to show up and there are no other codes to go with it.
I know its still not right since the plugs and fuel trims tell the story I havent seen it for a few weeks since adding injector cleaner.
It could be a coincidence, I added the injector cleaner then the weather warmed up both times. Last fall as it got cold the code retuned every few days until it was parked for winter. I used it twice on nicer days over winter and just cleared the codes until now, since now I am driving it daily again I can hopefully sort this.