Member Since: 05 Feb 2006
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Just finished with an RRS with poor drivability and a sickening hesitation from junctions and the odd random bong on acceleration. The owner's presumption was gearbox or turbo (it had done quite a few miles) and on the first check the LP pressure seemed fine.
After a trip round the block with various diagnostic things plugged-in we found the LP pump pressure fluctuating wildly every so often. Fault traced to a damaged and corroded wire near a connector. With the connector bypassed the vehicle runs really well and the apparent gearbox issue was nothing of the sort. It did not have any HP fault codes though, which seemed rather odd.
Unfortunately as part of a previous diagnosis the owner's indy had replaced the EGRs. I'm not sure this was actually required, so I hope he found a genuine reason to change them…. Land Rover - Turning Drivers into Mechanics Since 1948
Thank you for an informative article. I don't know much about Diesel engines and their ancillaries, but now I know a little more! I had no idea about the fuel warming/ cooling process.
I have a 2013 D4, is the Low Pressure fuel circuit similar ? I'm not aware of any problems with my own vehicle, but I like to know things!
6th Jun 2015 6:19 am
Robbie
Member Since: 05 Feb 2006
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Hello Treetrimmer,
The D3 and D4 LP fuel system are functionally the same, even if some of the pipework is slightly different. As it happens the diagram, pictures and screenshots on the first page are all from a 2013 D4.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 23 Jun 2006
Location: W.London.
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Should I be saying 'oh b*lls'?.......I should add that I have had no starting problems even in winter, and an odd thing is that the car starts and runs with this fuse completely removed ....... Can't check fuel pressure yet as gauge not arrived.
11th Jun 2015 9:06 am
Robbie
Member Since: 05 Feb 2006
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As said previously, the D3 pump does appear to draw less than the D4 pump, but yours is in the region where problems can arise (but not in all cases). Even with no symptoms I would probably be minded to check the LP pressure at some point, just to be sure and hopefully set your mind at ease.
The bit that has me stumped is being able to run the vehicle with no LP pump. I know the system would have been primed and that the weather is warm, but still a surprise.Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 23 Jun 2006
Location: W.London.
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Thanks Robbie, I will check the pressure when gauge turns up......... EDIT........tried it again today(Sunday 14th), a bit cooler OAT .......LP pump drawing 4.14A, so it's kinda reacting in the right way I suppose. Still runs with fuse removed, perhaps I have an HPFP capable of super suction
11th Jun 2015 9:50 am
DN D3 Decade
Member Since: 23 Jun 2006
Location: W.London.
Posts: 2344
I now have the px gauge, so did another check today....... Needle steady at just over 5 psi, if I revved up to say 3000 rpm the press dropped to just under 4 psi. It is soon due for a fuel filter change, so I will see if that alters anything. If nothing else, this demonstrates the difference between Robbies newish D4, and a nearly ten yr old banger like mine.
27th Jun 2015 2:46 pm
Robbie
Member Since: 05 Feb 2006
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You can't call it an old banger, the D3 will hear you!
It may be 9 years old, but the LP pump is still hacking it.
Thanks for the amp vs psi comparison - the more the merrier.
Land Rover - Turning Drivers into Mechanics Since 1948
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I was only whispering Robbie.
27th Jun 2015 3:17 pm
SteveNorman
Member Since: 14 Oct 2005
Location: Somerset
Posts: 1145
It's usual for a D3 pump to draw between 4 and 5 amps.
A good pump can go negative on pressure when under full acceleration on the road. -0.15 bar is acceptable/normal on a d3.I have confirmed that with a new pump also.
Problems occur in the range of -0.35 or more.
D4's seem to be better, even with the same 2.7 engine. ( I haven't got the figures to hand, as doing it by memory!)
And yes, they will run at little load with no fuse in, as the HPFP draws fuel up from the tank, but drive it and it won't go long with Christmas happening on the dash.
Regards
Steve
27th Jun 2015 4:08 pm
Robbie
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Cheers Steve!
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 23 Jun 2006
Location: W.London.
Posts: 2344
Yes, thanks Steve, I did pull the fuse momentarily with the gauge connected, it carried on running, but unsurprisingly, the needle cranked over to the red vacuum indication on the left of the gauge.I won't do that again for fear of cavitation.
27th Jun 2015 11:41 pm
M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8221
Excellent write-up Robbie excellent, how do you do it? - do you write it all in one go or have some method of producing it in stages and saving to upload somehow all in one go?
The gauge has got to be a must for every Disco owners toolbox As the pressure varies by model year it could be a good idea to check the pressure when the engine is running normally and make a note of them for future reference.
The only set back with using an air pump schrader connector is if they have any rubber components it will quickly deteriorate after being in contact with diesel.It can when others can't,
It will when others won't,
It goes where others don't.
Excellent write-up Robbie excellent, how do you do it? - do you write it all in one go or have some method of producing it in stages and saving to upload somehow all in one go?
Write, highlight, copy, paste, (preview,) submit? Current: Discovery 3 06MY (55 reg) HSE Auto Zambezi Silver Allisport Fast Road Intercooler, V8 Brakes, Silicone IC Hoses, EGRs Blanked, Remapped, De-Cat pipe, FBHIC
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I was only whispering Robbie. 
Allisport Fast Road Intercooler, V8 Brakes, Silicone IC Hoses, EGRs Blanked, Remapped, De-Cat pipe, FBHIC
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