Member Since: 05 Feb 2006
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M3DPO wrote:
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?
I usually have a rough plan in my head, take and upload the relevant photos and assemble the document as a simple plain text file to avoid any odd formatting issues creeping in. From there I just paste it in. The tone I aim for is usually dictated by the requests I get by PM - aiming at bright folk who have not tackled something like this before.
I'm not sure my guides match the achievements of others on here and my technical knowledge is dwarfed by some of the forum members, but I hope they help or at least stimulate people to give it a go.
Land Rover - Turning Drivers into Mechanics Since 1948
Last edited by Robbie on 28th Jun 2015 6:57 pm. Edited 1 time in total
28th Jun 2015 6:49 pm
M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8103
Very modest reply indeed It can when others can't,
It will when others won't,
It goes where others don't.
28th Jun 2015 6:56 pm
aman
Member Since: 09 Feb 2014
Location: London
Posts: 285
SteveNorman wrote:
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
Hi steve
Can I ask what is probably a silly question?
If the low pressure fuel pump runs at 4-5 amps in Discovery 3, and maybe 8-9 amps in Discovery 4, why is there a need to have a 25 amp fuse? Wouldn't a 15 amp fuse be enough?
Also, does the low pressure fuel pump stay on all the time?
When I was trying to test my low pressure fuel pump today, I put the ignition on (didn't start car), then I heard the low pressure fuel pump in the tank come on, but it went off after about 10 seconds
I haven't bought a pressure gauge yet, but I will put the pressure results up when I get one
Thanks
18th Jul 2015 9:25 pm
Robbie
Member Since: 05 Feb 2006
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In the absence of Steve, The usual fuse methodology is to protect the wiring not the component and to allow for inrush current and harsher operating conditions. You can imagine the viscosity of diesel at minus 30 deg C.
The pump is on for the initial prime and then turns off after 10 to 20 seconds or so. It is also turned off during start to preserve the amps for cranking and the plugs. Once the engine is running the pump runs all the time.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 14 May 2012
Location: Ellikom
Posts: 232
I've been reading this nice tread too and did some measurements myself.
Here an example of a BAD D3 LPFP: https://youtu.be/UrBs7LTciTc
Pressure is 0.25bar while idle running, revving makes the pressure drop to 0.1bar and (not visible on the video) during acceleration the pressure even goes negative!2017-...: Disco II Td5 auto, 1999, BAS remap, HD TC and auto box Ashcroft, Allisport IC, ACE, 2" lift only coils, BF goodrich KM2 265/70R17, FF front and rear bumper, TF steering guard and tree sliders, nanocom.
2013-2017: Disco 3 TDV6 HSE aut. of 2008, Britpart treesliders, IIDTool, RLD sump guard, BFG KM2 265/70R17, adj. rods, BAS remap + EGRs blanked, silicon IC hoses.
2010-2013: Disco II Td5 of 2000, ACE, front Bearmach HD coils, rear SLS, GG AT2
14th Aug 2015 2:59 pm
aman
Member Since: 09 Feb 2014
Location: London
Posts: 285
Thanks Robbie!
Just checked my fuel pump fuse and it is drawing 4.50Amps (2005 Discovery 3 TDV6)
This is with a brand new denso alternator giving out 15.0V
Haven't had a chance to check the LPFP pressure yet
Where are you based by the way?
Also, regarding the Amps/Psi readings, my local Landrover Guy advised me that it is also worth checking the voltage of the system (as alternator is not always giving the same voltage in all cars), as increasing the voltage may have an effect on the number of amps that the pump draws?
Will a higher voltage mean less amps etc (I'm not too good with the calculations unfortunately)
Cheers
Robbie wrote:
In the absence of Steve, The usual fuse methodology is to protect the wiring not the component and to allow for inrush current and harsher operating conditions. You can imagine the viscosity of diesel at minus 30 deg C.
The pump is on for the initial prime and then turns off after 10 to 20 seconds or so. It is also turned off during start to preserve the amps for cranking and the plugs. Once the engine is running the pump runs all the time.
19th Sep 2015 10:53 am
Robbie
Member Since: 05 Feb 2006
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I'm based in Gainsborough, Lincolnshire. If you click on the location link in the members profile it will give you a rough idea where members are (for those that actually fill it in).
You have been advised correctly as the change in voltage with a set load will change the current draw. The voltage output of the D3 alternator is controlled by the main computer according to battery state of charge and the inferred temperature of the battery.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 09 Feb 2014
Location: London
Posts: 285
Thanks Robbie
By the way - can I measure the fuel pressure from the schraeder valve with a digital tyre pressure gauge?
20th Sep 2015 1:10 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
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An interesting D3 in my garage today. Symptoms included a hesitation, an intermittent rhythmic 'throb' at idle RPM and RPM decay with steady throttle.
After the usual health-check, fault codes and live data of engine controls my initial suspicion was injectors, but these appeared ok. The amp draw of the LP pump was ok at 4.7 amps with a steady output on a Fluke in fast min/max mode.
Fuel pressure at the schrader was 5 PSI and steady on the prime. With engine running the PSI oscillated by nearly 1 PSI, with the pressure dip in time with the rhythmic 'throb'. With gentle throttle the PSI dropped further and down at under 3 PSI at 4000 RPM with no load.
Not wishing to condem a pump on just the pressure alone and with an apparently healthy current draw I broke out the scope, connected via an amp clamp to the fuel pump circuit:
Click image to enlarge
I didn't have time to make the scope capture pretty, or a USB stick to hand to do proper screen grabs, but the picture shows the current ripples caused by the impeller over around 4 complete rotations:
Click image to enlarge
Click image to enlarge
For those that like counting discrete peaks you can see that the pump has 8 bars, but that some of them pull very little current in comparison with others. This suggests that some impellers have been stripped away or worn commutators. You can also use the waveform to check for open or shorted armatures or calculating pump RPM too.
With 2 demonstrable and complementary metrics (scope and pressure) hopefully this will be a parts sniper rather than a parts cannon.
Edit: I've been asked what causes fuel pump failures. Clearly blocked filters will increase the load on the motor and produce additional heat. Heat is the real killer of the motors and the design uses the fuel bath it sits in as a means of shedding heat. If you are one of those who likes to run the vehicle with a consistently low fuel level and only partially fill the tank then you are doing your fuel pump no favours.
Sorry if this is all a bit geeky!
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 09 Feb 2014
Location: London
Posts: 285
Very impressive Robbie!
Would it be possible for you (if you get time) to also do a scope trace on a known good pump (say on a newer car) to show us what a good trace should look like too?
Cheers!
30th Sep 2015 11:33 pm
DG Site Moderator
Member Since: 12 Dec 2005
Location: The Gaff
Posts: 50934
Robbie wrote:
An interesting D3 in my garage today.
Are you Jay Leno ? 21 year LR veteran > D2 GS 2003 > D3 S 2006 > D3 HSE 2009 > D4 HSE 2013 > D4 HSE 2015 > D5 HSE 2018 > DS HSE R-Dynamic P300e 2021
30th Sep 2015 11:47 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
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Well I found it interesting and whilst I looked around for Jay to ask questions it transpired that it really was my garage!
8)Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 05 Feb 2006
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Geek mode - On
In answer to a question for those without a oscilloscope, yes it is possible to use a RMS capable DMM to check the relative health of the LP pump's DC motor.
As the motor rotates the brush has intermittent contact with the commutator the current used by the pump will be a pulsating (on/off) DC current. As the brushes and/or the commutator start to fail the contact pattern will degrade giving an uneven current draw, detectable in AC mode. As the amount of ripple current increases the amount of DC current will reduce and the pump will be able to do less work.
The simple upshot is that a good pump will have an AC current value of 10% or lower than that of the DC current value. A really bad pump could have an AC current close to the full DC value. If the AC current is about 50% of the DC then the pump has had its day. So test the current at the fuse in both DC and AC modes.
Geek mode - Off
Land Rover - Turning Drivers into Mechanics Since 1948
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