Fault Codes U2023 and P0087

[Lukeis]

Hi Gents

Tonight while driving home I received the above fault codes, lost significant amount of power and the lights "Gearbox error" and "Restricted Performance" illuminated on the dash.

Ive read the codes as follows:

U2023 - Gearbox - control module network signal calibration data
P0087 - Engine Management - Fuel rail/system pressure - too low

Was hoping for suggestions of things to do/check tomorrow..

1) Replace fuel filter
2) Check battery voltage
3) is there a fuel pump filter? if so, where is it?
4) anything else I can check myself?

[LRD414]

Fuel filter, LPFP and HPFP are all possible suspects, in order of cost. The LPFP is in the tank.
Have a read of this:
DISCO3.CO.UK - View topic - Robbie's Guide To The Low Pressure Fuel System (http://www.disco3.co.uk/forum/topic130062.html?highlight=p0087)

Scott

[orville]

Hi Gents

Tonight while driving home I received the above fault codes, lost significant amount of power and the lights "Gearbox error" and "Restricted Performance" illuminated on the dash.

Ive read the codes as follows:

U2023 - Gearbox - control module network signal calibration data
P0087 - Engine Management - Fuel rail/system pressure - too low

Was hoping for suggestions of things to do/check tomorrow..

1) Replace fuel filter
2) Check battery voltage
3) is there a fuel pump filter? if so, where is it?
4) anything else I can check myself?

What was the outcome I have the same errors?

[BradC]

What was the outcome I have the same errors?

Want to borrow my fuel pressure gauge? I cable-tied it to the windscreen wiper and drove until it faulted. That ruled out the LPFP & Filter, leaving only the HPFP as the potential culprit.

[orville]

I have a gauge, I bought one to test lpfp. I guess the outcome is obvious, trying to eliminate everything before jumping into a new hpfp.

[BradC]

I have a gauge, I bought one to test lpfp. I guess the outcome is obvious, trying to eliminate everything before jumping into a new hpfp.

As mine was all but undriveable last week, I "tickled" the PCV on the HPFP last Saturday which put the fault into remission for about 500k's, but it came back last night. I have a few other things to try, but I know ultimately it's going to need a new pump. I'm just prolonging the inevitable while trying to get a more detailed understanding of the exact failure mechanism.

[orville]

Thanks for the feedback, I will pass it on to my son. I have trawled the internet for ideas and found nothing. Even looked at Ford and Peugeot motors. Read discussions about the merits of two stroke oil (snake oil?) . I think he is going to take out the lpfp and clean the filter as a possibility.

[BradC]

Thanks for the feedback, I will pass it on to my son. I have trawled the internet for ideas and found nothing. Even looked at Ford and Peugeot motors. Read discussions about the merits of two stroke oil (snake oil?) . I think he is going to take out the lpfp and clean the filter as a possibility.

Which is why I suggested using the gauge. You can actually watch the low-side pressure as the fault occurs. If it doesn't move (like mine) then there would be no point dropping the tank to get the LPFP out and you'd rule out the filter and associated pipework at the same time. Of course if the low-side pressure tanks as the fault occurs then you have more reason to tear into the fuel supply system.

[orville]

I will try your idea.

[Ean Austral]

As mine was all but undriveable last week, I "tickled" the PCV on the HPFP last Saturday which put the fault into remission for about 500k's, but it came back last night. I have a few other things to try, but I know ultimately it's going to need a new pump. I'm just prolonging the inevitable while trying to get a more detailed understanding of the exact failure mechanism.

Found this part interesting , how did you tickle the PCV on the pump. ??

Cheers Ean

[BradC]

Found this part interesting , how did you tickle the PCV on the pump. ??

I manually exercised the valve 5 times. I took a look at the way the ECU drives the valve and figured it was quite gentle in the way it drives the valve closed. I figured if I closed it with "extreme prejudice" if it was grunge in the valve I might just shift it.

I used a pair of crocodile clips and a 12V 1.2AH SLA battery to force the valve closed and got a nice satisfying "click". The valve is quite low impedance, so I wanted a 12V source that was inherently current limited. The cheap, half discharged battery I used did the job. It's only good for less than 2A of current.

I'm going to order a new pump this week, but I'm also going to try a few other ideas with increasing levels of lunacy, because I can.

[Ean Austral]

I manually exercised the valve 5 times. I took a look at the way the ECU drives the valve and figured it was quite gentle in the way it drives the valve closed. I figured if I closed it with "extreme prejudice" if it was grunge in the valve I might just shift it.

I used a pair of crocodile clips and a 12V 1.2AH SLA battery to force the valve closed and got a nice satisfying "click". The valve is quite low impedance, so I wanted a 12V source that was inherently current limited. The cheap, half discharged battery I used did the job. It's only good for less than 2A of current.

I'm going to order a new pump this week, but I'm also going to try a few other ideas with increasing levels of lunacy, because I can.


mmm if you managed to force it using a seperate power source , I wonder if the issue with these cars is not the pump but the electrical connectors that operate that side of the pump.

cheers Ean

[DiscoJeffster]

mmm if you managed to force it using a seperate power source , I wonder if the issue with these cars is not the pump but the electrical connectors that operate that side of the pump.

cheers Ean

TBH I’ve had two connectors that have required contact cleaning to resolve. The steering wheel switch connector and front speaker connectors. Both were giving poor connectors. Would be interesting to apply a good contact clean to the male and female side of the HPFP and see if it behaves.

[Ean Austral]

TBH I’ve had two connectors that have required contact cleaning to resolve. The steering wheel switch connector and front speaker connectors. Both were giving poor connectors. Would be interesting to apply a good contact clean to the male and female side of the HPFP and see if it behaves.

that will be my next move , checking the electrical side before I do a pump change .

Cheers Ean

[BradC]

Would be interesting to apply a good contact clean to the male and female side of the HPFP and see if it behaves.

I did that months ago. The ECU is pretty good at picking a duff connection on those solenoids as they are such a low resistance (and setting a code). Also given my particular failure mode can be "driven around", I'm not really suspecting an electrical fault.

Don't let me stop you trying however. I'd love to be proven wrong.

One thing I have noticed looking at the various PCV constructions is they all seem to use a flooded design, where fuel is used to cool the solenoids. That'd make the ingress of grunge or gum quite likely to cause issues. What I can't reconcile is anything large enough to cause the solenoid to gum up or stick should be large enough to either block and injector or be prevented from reaching the pump by the filter.

[orville]

Would you consider the gauze filter on the lpfp as a source of gunge? Our tests show the fuel pressure drops when the accelerator is applied.

[BradC]

Would you consider the gauze filter on the lpfp as a source of gunge? Our tests show the fuel pressure drops when the accelerator is applied.

If the filter sock is a source of grunge it should get caught in the main filter.

I would expect the fuel pressure to drop when the accelerator is applied. Mine starts at 0.4 bar, that drops to 0.3 bar under running conditions and drops to slightly under 0 bar when doing a full noise blast in 3rd gear. Oddly enough under heavy braking it rises to nearly 0.5bar.

Thats all within spec, even if a bit low. The important part for me was the fuel pressure never drops when the HPFP faults. It stays a solid 0.3bar. As far as I'm concerned that rules out the low pressure system.

i had to drive 50ks with the gauge cable-tied to the windscreen wiper arm until it played up.

[orville]

We did the same pressure test on a working D4. Pump doesn't drop below 0.5 bar when running and lowest is ,0.4 under revs to 4000. The D3 drops to 0.2. The D3 fails when coasting or gliding but not under acceleration. Not convinced it is the Hpfp.

[Ean Austral]

We did the same pressure test on a working D4. Pump doesn't drop below 0.5 bar when running and lowest is ,0.4 under revs to 4000. The D3 drops to 0.2. The D3 fails when coasting or gliding but not under acceleration. Not convinced it is the Hpfp.

I am going thru the same issue with my D3. Faults only when coasting , code is Low fuel rail pressure, but only if you shut it down as soon as it faults. If you let it run the faults grow to include a gearbox fault , suspension fault , park brake fault and lucky if you can do 20km/h. Bloody scary when you have a 3 trailer road train up your clacker with no where to pull off the road.

I also struggle to believe the issue could only be the HPFP , as it is so random , I am going to spend some checking the electrical side of things , altho I have purchased a HPFP plus the other bits needed for a pump change.

Cheeers Ean

[BradC]

I am going thru the same issue with my D3. Faults only when coasting , code is Low fuel rail pressure, but only if you shut it down as soon as it faults. If you let it run the faults grow to include a gearbox fault , suspension fault , park brake fault and lucky if you can do 20km/h. Bloody scary when you have a 3 trailer road train up your clacker with no where to pull off the road.

Have you tried turning it off and back on again? Then again, I'm not sure what might happen with an auto, but with the manual box I just flip the ignition off and back on and keep driving. With the van on the back I don't even feel it as it only ever happens under low load while cruising.

In my case I am absolutely *convinced* it's the HPFP, specifically the PCV sticking. I can see it stick on the live data from the IID. The system calls for more juice, the PCV is commanded to close and that continues until the duty cycle reaches about 55%, sits there for 2 seconds and the fault is raised. When I see the duty cycle shoot past 40% I get off the throttle and back on again. That makes the ECU drive the valve back open and when it is subsequently commanded closed as I get back on the pedal (most of the time) it shoots past the sticky point and all is good.

If it was the LPFP or associated filters/pipe work a cycle of the throttle pedal wouldn't make a difference and I'd see it on the low pressure gauge as the fault was occurring. If it was a physical fault in the HPFP itself I wouldn't be able to get sufficient fuel pressure, and yet I can get >1600 bar under full load immediately after the fault was driven around. If it was a wiring or connector fault I wouldn't be able to drive around it, the ECU would be incapable of making the valve go where it wants. Therefore it *must* be the PCV, and as they can't be changed independently of the HPFP, by extension it requires replacement.

I have one more thing to try, and this is the longest of long shots with plenty of potential for disaster.

The VW community swears by Liqui-Moly Diesel Purge. Diesel Purge is a light refined hydrocarbon and a cetane improver (to make it burn more like diesel and stop it blowing holes in pistons). The light refined hydrocarbon cleans deposits that diesel doesn't. It's basically what the yanks call naptha or we know as Shellite. I keep litres of the stuff around as it's the ducks nuts for cleaning anything exposed to engine grunge. It works on deposits that both petrol and diesel find hard to move (yes I've tested that many times) and evaporates without a trace.

So, my last resort is to make ~8L of my own "diesel purge", drain the tank/filter, put this mixture in the tank and run the PVC & VCV through several "crank the engine, exercise the valves" cycles to see if it cleans them out. If I put the return line from the pump into a jar it should be obvious if *any* cleaning is occurring. The cetane improver in "Diesel Purge" is 2-Ethylhexyl nitrate, and Amsoil make a "cetane boost" which is entirely 2-Ethylhexyl nitrate. So some of that, Shellite and a bit of lubricant should do the trick.

I have a spare rail pressure sensor, and according to the Siemens writeup on the ECU it won't even try to fire the injectors until it sees a pressure > 150bar. So having the spare plugged in reading 0 should mean it never tries to fire up and I can just cycle this stuff through the fuel system.

I'm pretty convinced the actual fault is wear in the valves (in exactly the same manner that makes the AC compressor displacement valves stick), but until I can get one to dismantle that remains a best guess.

Anyway, best case it prolongs the life of the HPFP. Worst case something goes wrong and I kill the in-tank pump, destroy 6 injectors and burn holes in pistons.

I already have a new pump and associated hardware in my LR-direct shopping cart, I'm just waiting on "an opportune budgetary moment". In the mean time, I might just see how much more damage I can do.

[Ean Austral]

MMM Shellite , know it very well.

Electrician cleaning a 200KVA alternator on our trawler many years ago , had vent fans on etc but must have built up the fumes in 1 corner of the engine room , battery charger cut in and KABOOM.

buckled the 8mm deck plating , tore the exhaust bellows clean off the engine due to the deck lifting and a piece of 20mm stainless rod that was sitting on top of 1 of the engine room hatches was found on a roof about 100mtrs away. Luckily nobody died , but 2 very deaf and burnt electricians were eventually removed looking worse for wear.

Off topic I know but I haven't heard shellite mentioned since so it bought back memories of that event.

No I haven't tried the turn off / on thing as its usually my wife driving the car so not game to tell her to try it.

Cheers Ean

Cheers Ean

[orville]

Sounds like a dangerous attempt to find a solution. Your analysis of the valve would seem to be on the money. I guess that is why in the UK they have exchange pumps available.

[BradC]

No I haven't tried the turn off / on thing as its usually my wife driving the car so not game to tell her to try it.

That was my problem. It *was* the wifes car. She handed me the keys and said (not unjustly) "If you want to keep this piece of ****, *you* drive it, I'm done".

(the rantings of an inebriated fool deleted)

[Ean Austral]

That was my problem. It *was* the wifes car. She handed me the keys and said (not unjustly) "If you want to keep this piece of ****, *you* drive it, I'm done".

(the rantings of an inebriated fool deleted)

well after the last weeks effort I think I will be getting the keys to the D3 plus the bill for her new car if this don't get sorted soon.
Anyway the car is booked in to the local guru up here late this coming week with the instructions either find a issue quickly or replace the HPFP with the one I just bought. Was going to do it myself but just started a new job and am working the next 14 days straight and I think by then I will be about $50k poorer and looking at a new car in the driveway .

Cheers Ean

[Rsys]

well after the last weeks effort I think I will be getting the keys to the D3 plus the bill for her new car if this don't get sorted soon.
Anyway the car is booked in to the local guru up here late this coming week with the instructions either find a issue quickly or replace the HPFP with the one I just bought. Was going to do it myself but just started a new job and am working the next 14 days straight and I think by then I will be about $50k poorer and looking at a new car in the driveway .

Cheers Ean

Was it the HPFP? I have the same issue and suspect some dirt ingress after both heads were rebuilt. Drives perfectly then when you’re just cruising it’ll fault with Low Fuel Rail Pressure. Stop, restart and it’ll either drive for 500 miles or 1 mile before faulting again.
I have one injector reading 1314 so out of range but can’t see that would throw a low fuel rail pressure fault. LPFP checked and new filter installed and still does it time to time.

[BradC]

Was it the HPFP? I have the same issue and suspect some dirt ingress after both heads were rebuilt. Drives perfectly then when you’re just cruising it’ll fault with Low Fuel Rail Pressure. Stop, restart and it’ll either drive for 500 miles or 1 mile before faulting again.
I have one injector reading 1314 so out of range but can’t see that would throw a low fuel rail pressure fault. LPFP checked and new filter installed and still does it time to time.

Eans been off the board for a break, but yes it was. I have his HPFP on my bench awaiting a teardown along with mine.

[Rsys]

Eans been off the board for a break, but yes it was. I have his HPFP on my bench awaiting a teardown along with mine.
Thanks for that. I’ve had several garages try to diagnose this without fail because they can never reproduce it. Don’t know if you know but could an out of range injector cause that error? And I’m left wondering what the garage did in the rebuild to break the HPFP like this

[BradC]

Thanks for that. I’ve had several garages try to diagnose this without fail because they can never reproduce it. Don’t know if you know but could an out of range injector cause that error? And I’m left wondering what the garage did in the rebuild to break the HPFP like this

Could have been nothing. I spent months diagnosing mine precisely because it was hard to reproduce, but eventually it got frequent enough I could watch it actually faulting in real time on the IIDTool once I knew what to look for. If the injector was spilling badly then I suppose in theory it could cause low rail pressure. I wouldn't bank on it though.

I got to the point I was driving through it. "Bing", off the accelerator, key off, key on, back on the accelerator. If you catch it early enough it doesn't cause cascade faults and I could just keep driving. Infuriating when it happens from every 10 to every couple of minutes on a 4 hour drive and you can't just pull over and set fire to it.

[Narangga]

Rsys - Ean explained the eventual fix to his problem here:

Not sure if im unlucky or lucky (https://www.aulro.com/afvb/l319-discovery-3-and-4-a/269511-not-sure-if-im-unlucky-lucky.html)

[Rsys]

Could have been nothing. I spent months diagnosing mine precisely because it was hard to reproduce, but eventually it got frequent enough I could watch it actually faulting in real time on the IIDTool once I knew what to look for. If the injector was spilling badly then I suppose in theory it could cause low rail pressure. I wouldn't bank on it though.

I got to the point I was driving through it. "Bing", off the accelerator, key off, key on, back on the accelerator. If you catch it early enough it doesn't cause cascade faults and I could just keep driving. Infuriating when it happens from every 10 to every couple of minutes on a 4 hour drive and you can't just pull over and set fire to it.

Lol. Unfortunately mine is an auto and the BING coincides with TRANSMISSION FAULT So it’s too late. However, having read this thread a couple of months back, I’ve been driving by taking my foot off the gas where I think it would normally fault like a shallow incline.
I would think a leaking injector should throw a Low Injector Pressure fault and not the fuel rail. Who knows? It’s a disco!

My rebuild happened after the dreaded oil pump failure.

One weird thing I have. If I pull the LPFP fuse, the LPFP still runs. Figure that one out. I’ve concluded that on a disco 3, nothing is as it seems

[BradC]

One weird thing I have. If I pull the LPFP fuse, the LPFP still runs. Figure that one out. I’ve concluded that on a disco 3, nothing is as it seems

That is indeed peculiar. If I pull the LPFP fuse the car still runs, but that's relying on the feed pump in the HPFP to pull fuel up from the tank. The LPFP is certainly not running.

I wonder where it's getting power from, and if it's a reliable circuit?

[Rsys]

That is indeed peculiar. If I pull the LPFP fuse the car still runs, but that's relying on the feed pump in the HPFP to pull fuel up from the tank. The LPFP is certainly not running.

I wonder where it's getting power from, and if it's a reliable circuit?

That’s the only thing stopping me from replacing the HPFP. Where is the LPFP power coming from? If I take the fuse out and put the ignition on I can hear the pump run for the 15 seconds. It suggests a short somewhere and as you say, it may be not be a reliable circuit tripping out occasionally.

[DiscoJeffster]

Lol. Unfortunately mine is an auto and the BING coincides with TRANSMISSION FAULT So it’s too late. However, having read this thread a couple of months back, I’ve been driving by taking my foot off the gas where I think it would normally fault like a shallow incline.
I would think a leaking injector should throw a Low Injector Pressure fault and not the fuel rail. Who knows? It’s a disco!

My rebuild happened after the dreaded oil pump failure.

One weird thing I have. If I pull the LPFP fuse, the LPFP still runs. Figure that one out. I’ve concluded that on a disco 3, nothing is as it seems

Why do you think it’s still running? Because it keeps running? Refer to Brads comment that the HPFP can successfully draw through it, albeit not effectively.

[Rsys]

Why do you think it’s still running? Because it keeps running? Refer to Brads comment that the HPFP can successfully draw through it, albeit not effectively.

Sorry. Extra explanation. If I pull the fuse, then put the ignition on I can hear the pump run for it’s 15 seconds before the relay kicks it off. If I replace the fuse, exactly the same. So the relay is getting power from somewhere but it doesn’t look like it’s from fuse 1. Which is why I am so baffled.

[BradC]

Sorry. Extra explanation. If I pull the fuse, then put the ignition on I can hear the pump run for it’s 15 seconds before the relay kicks it off. If I replace the fuse, exactly the same. So the relay is getting power from somewhere but it doesn’t look like it’s from fuse 1. Which is why I am so baffled.

I’d certainly be looking into that. Unfortunately unless your P0087 occurs under heavy load then it’s unlikely the Power source to the LPFP is the issue.

[Rsys]

I’d certainly be looking into that. Unfortunately unless your P0087 occurs under heavy load then it’s unlikely the Power source to the LPFP is the issue.

No. Mine is under normal driving usually either on the flat or slight incline. Boot it and it’s fine. I’m certain it’s the HPFP but before the rebuild it was fine so something happened during the rebuild - either some dirt ingress or damage in some way

The rebuild was a total abortion by the garage. Leak off pipes leaking onto the exhaust (that was a fun journey). Both rockers leaking. Servo pump seal leaking. I even told them to blank off the EGRs (which had been software deleted) and that wasn’t done.

I’m loath to get rid of the car because so much of it is as new now.

I’m actually in the U.K. and used to run a pub right next to Britpart and know some of the management from those days. The reason I came across this forum was that the symptoms matched mine exactly ie none of this brake switch stuff.