Member Since: 11 Apr 2013
Location: Bedworth
Posts: 394
Low Pressure Fuel pump Scope (Playing with new tool)
Just bought a 4 Channel PicoScope (thought I would treat myself)
Car has a history of rough running and a lack of power on acceleration, also when cold it would try to stall when stopping at junctions (until run for a few miles). The engine has a low down knock on idle also.
After reading Robbies very good guide on the low pressure fuel system.
First thing was to test voltage and earth at the low pressure fuel pump fuse in the engine bay, all good there. Next was to break out the fuse extension lead and use a current clamp to check the current or the pump when running. (See pic below)
from the above image pump not pulling an even current.
Next did a scope using a pressure transduce and the current clamp.
The red line is the pressure, the dip is when I did a full throttle request pressure dropped off more than I would expect.
The diagram below is a zoomed in image of the same scope.
My conclusion is the low pressure fuel pump tank is worn and requires replacing. It can't keep pressure when demand requires.
I thought I would share my findings and get further opinions from the experts on here. All opinions welcome.
Member Since: 05 Feb 2006
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Nice extracts from the Picoscope - wish I could afford one!
I'd agree that the pump is a little tired but it is far from the worst I have seen. The trace from all 8 commutators is smooth but it does have a regular roll-off where the current it pulls is lower (with a corresponding dip in output) so there does not appear to be a blockage or a bad filter.
Using the cursors you you can measure the time from one significant feature until it repeats again. From this you can calculate the pump rpm. The Picoscope may even have a tool to do this for you.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 11 Apr 2013
Location: Bedworth
Posts: 394
Robbie,
I changed my pump not pulling much more than amperage than old pump but a better wave. Will post the images in the next couple of days. Going to try a new relay to see if I can get it to pull more amps. Only getting about 5.6psi of pressure at schraeder off the top of my head.Vehicles
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22nd Feb 2016 10:24 pm
Robbie
Member Since: 05 Feb 2006
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Looking at your original trace above more carefully it appears to take 18 ms for the waveform to repeat. With 60,000 ms to a minute that equates to just 3,330 rpm.
It is a shame that we are probably comparing apples and pears with D3 & D4. I'll try to remember to do a few screenshots from the next D3 I see.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 11 Apr 2013
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New Fuel Pump Trace Zoomed in showing much more even current
New fuel pump trace with a Wide open throttle pressure drop.
WOT throttle pressure drop.
New Fuel pump showing RPM calculation in bottom right.
Next is to see if a new fuel pump relay has any affect on the pressure output
Rob think we need a scoping weekend of both a D3 & D4 to get bench mark figures of know good components. Vehicles
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23rd Feb 2016 11:28 am
Robbie
Member Since: 05 Feb 2006
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Wow, quite a change from the old pump. Nice waveform, with the pump spinning at nearly twice the speed and maintaining a good positive pressure on a throttle snap - I have seen some sickly D3 pumps go negative on such snaps.
If you are concerned that you may have resistance somewhere in the fuel pump circuit then a voltage drop check when the tank was lowered would have helped.
I must build myself a couple of pressure transducers for my scope - another thing on the to-do list!
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 11 Apr 2013
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Rob,
Take it that is a pic of a Canbus signal. I bought the pico Canbus break out box. When I finally get the disco back on the road time to play properly with the tool.
Glow plugs,
Crank case pressure
Valve timing wave
Injectors v crank v cam timing
Injectors and back pressure
MAP sensor
Oil pressure /sensor
Etc
Some much to test.Vehicles
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2005 D3 HSE Silver
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(A bit Off Topic!) How's the bottom end of the engine now?Mark.
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23rd Feb 2016 10:23 pm
Valhalla
Member Since: 23 Oct 2011
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brightyuk wrote:
Rob,
Take it that is a pic of a Canbus signal. I bought the pico Canbus break out box. When I finally get the disco back on the road time to play properly with the tool.
Glow plugs,
Crank case pressure
Valve timing wave
Injectors v crank v cam timing
Injectors and back pressure
MAP sensor
Oil pressure /sensor
Etc
Some much to test.
Have you checked the Pico Automotive reference waveforms? I've tried to post one or two things there, as I have been frustrated in the past by not having some to hand. I've been using Pico gear (in various levels) since 2004, or thereabouts, and it's now an integral part of my business. I sound like a Pico salesman......
Agree with Robbie that you seem to have a restriction in the fluid path of your LP fuel system; your electrical traces don't seem all that bad (even the early ones) but the pressure transducer trace (at the Schraeder?) is pretty poor. Do you have any data from the rail pressure sensor to back-up a loss of rail pressure under WOT testing (or a delay in pressure build-up)?
The most obvious culprit would appear to be your pressure regulator, but I wouldn't rule-out a fuel line restriction (maybe a filter head problem?)
24th Feb 2016 12:23 am
al cope
Member Since: 08 Nov 2005
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if the pressure regulator is at fault, its a HPF replacement, as you cant get the regulator on its own
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24th Feb 2016 9:17 am
Robbie
Member Since: 05 Feb 2006
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Just ordered a couple of pressure transducers from HK for just under £20. No doubt they will be on the slowest boat possible, but I will post my traces when they arrive.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 11 Apr 2013
Location: Bedworth
Posts: 394
anglefire wrote:
(A bit Off Topic!) How's the bottom end of the engine now?
That is job for Friday this week to strip the bottom end and see if anything going on.
Valhalla wrote:
Agree with Robbie that you seem to have a restriction in the fluid path of your LP fuel system; your electrical traces don't seem all that bad (even the early ones) but the pressure transducer trace (at the Schraeder?) is pretty poor. Do you have any data from the rail pressure sensor to back-up a loss of rail pressure under WOT testing (or a delay in pressure build-up)?
The most obvious culprit would appear to be your pressure regulator, but I wouldn't rule-out a fuel line restriction (maybe a filter head problem?)
Valhalla Thanks your help.
Would you expect the trace to read higher or be smoother?
I thought the pressure regulator was attached to the low pressure fuel pump which has been replaced. I have also changed the fuel filter.
I have a new relay so will fit that and re-scope and get some live data using the IID of the rail pressure sensor or pressure delay.
I will post further.
Robbie,
much cheaper than the picos cope version Vehicles
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