WPS500X Pressure transducer back leakage tests

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WPS500X Pressure transducer back leakage tests

Postby Steve Smith » Tue Jul 01, 2014 12:02 pm

I would like to post and share this test procedure using the WPS pressure transducer as your feedback would be most valuable.

Possibly one of the most valuable and conclusive test procedures we have when diagnosing common rail diesel systems is the “Spill Test” or “Back leakage test”

Spill or back leakage is an essential feature of the common rail diesel systems confirming adequate lubrication of the injector assemblies, whilst providing a degree of cooling as a beneficial side effect.

Traditionally we have measured the volume of “back leakage” using graduated collection bottles, whilst monitoring both the rate and amount of “fill” during cranking or pre-set running conditions.

The back leakage test will always remain relevant as manufactures often specify the volume of back leakage against time (Cubic Centimetres per seconds CC/S)

There is however an alternative using the WPS500X pressure transducer that offers some additional advantages.

1. Connecting the WPS in series with the injector spill return hose will enable the technician to measure the back leakage pressure/pulsations under numerous engine speed and load conditions. The technician can now monitor the contributing back leakage pressure from each injector whilst road-testing the vehicle under the conditions described by the customer or DTC “freeze frame data”.

2. The WPS500X pressure transducer will need only one connection into the back leakage return pipework as opposed to disrupting 4 x injector spill hoses on a four cylinder engine.

3. Using the WPS transducer in conjunction with PicoScope will provide a hard copy of test results including any relevant engine test conditions such as RPM, MAF, MAP Fuel Pressure etc. This builds customer confidence and provides feedback to warranty/insurance companies.

After connection, start the engine and allow the back leakage to bleed through the spill test pipes, WPS pressure transducer, then on into the sealed container.

With the WPS transducer and spill hoses bled, you will now be able to monitor the back leakage pressure and using the signal from number 1 injector, identify the pulsations using the firing order.

When using the scope we are always looking for uniformity/anomalies and should all injectors be performing equally, (balanced) we should see even pulsations within the back leakage waveform

Should you identify any irregularity, by using the additional number 1 injector signal and the firing order sequence you will be able to identify the offending injector and act accordingly?

Note: Using the WPS transducer will enable back leakage evaluation under road test conditions so capturing those illusive, intermittent running issues.

BACK LEAK IMAGE 2.jpg


Below is an overview of the back leakage pressure under idle to WOT conditions. The crankshaft signal (Blue) indicates the engine speed, the back leakage pressure is indicated using channel B (Red) revealing the various stages of back leakage pressure. Using the zoom feature of PicoScope you are able to zoom into any area of this capture and monitor the back leakage pressure under various engine running conditions. Notice on over-run how the back leakage pulsations clear during the “fuel cut stage” (No injection=no pulsation)

OVER VIEW OF WOT SPILL TEST.jpg


Below is a zoomed image of the WOT to the over-run stage

SPILL TEST ZOOM.jpg


BACK LEAKAGE TEST.psdata
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Re: WPS500 Pressure transducer back leakage tests

Postby volrem » Tue Jul 01, 2014 4:31 pm

This is great idea and proves that there are unlimited possibilities to use it.

Now i have to finally get one also. :P
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Re: WPS500 Pressure transducer back leakage tests

Postby Liteace » Thu Jul 10, 2014 2:53 pm

What CR system was tested using this method, Siemens, Delphi or Bosch ?
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Re: WPS500 Pressure transducer back leakage tests

Postby Steve Smith » Thu Jul 10, 2014 2:58 pm

Hello Liteace, the system tested was a Bosch EDC 15C

I hope this helps?

Take care......Steve
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Re: WPS500 Pressure transducer back leakage tests

Postby HC_CDC » Sat Jul 12, 2014 3:41 pm

Great investigation Steve.

How would you explain that the return channel pressure actually starts to rise before the pilot valve is lifted?
I can`t find any explanation yet..

Cheers,

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Re: WPS500 Pressure transducer back leakage tests

Postby Steve Smith » Tue Jul 15, 2014 2:13 pm

Hello Henk and thank you for the feedback and challenging question.

This is one of those questions that requires some research and composure as I am not sure I have the answer.

Thinking through the whole “spill” process you would expect the peak in spill pressure to align directly with the injection open event, and in the above case injectors 1 and 3 are not far away but injectors 4 and 2 do not align with the peak.

They are most certainly early in relation to the peak and also happen to be the injectors with the lower spill pressure! (Not sure of the relationship here and so really need to do more work)

I have been looking at numerous spill waveforms and have noted a variety in alignment of peaks and troughs within the spill pattern. (One of which is a Peugeot where the trough aligns with the opening of the injector as opposed to the logical peak!)

I have also noted how spill peaks can align perfectly with some injection open events at idle, but misalign during acceleration to align again on return to idle speed.

We have to be aware of a number of issues here and one of which would be the level of spill when the injector is not open/injecting, as there will be a degree of back leakage proportional to common rail pressure and integrity of the injector assembly.

Injector compensation and adaptions may also come in play when looking at the uniformity of spill pressure especially during acceleration and “smooth idle control” (cylinder balance)

What is most important here has to be the pressure value of each peak and the uniformity between them.

Here is where our “back to back” testing comes into play, sharing waveforms with colleagues, testing vehicles without any running issues and the waveform library.

With hind sight I wish I had isolated an injector whilst carrying out the above test to look at the effects on the spill pattern. (Certainly a must for the next test)

I hope there is some value in the above, take care….Steve
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Re: WPS500 Pressure transducer back leakage tests

Postby HC_CDC » Wed Jul 16, 2014 8:42 pm

Hi Steve,

Thanks for your thoughts, as you say, not really a "that must be it" explanation.
A while after I posted the question it suddenly came to me that it could well be that what you see is a delayed pressure pulse after the injector fires. We have to take into account that the back leakage/control spill hoses are soft, depending on their age they will first expand a bit on a pressure pulse and therefore work as a sort of hydraulic accumulator, this and the distance between the sensor and the actual injector will determine the delay you see. Don't know if you have a lab for these tests and a PICO budget but you could try to make as much as possible the return lines of hard tubing,up to some 10 cm after the sensor tie-in point, connecting with only short rubber hoses to the injector and see if that proves the assumption or not, what do you think? If so the test is interesting but has too many variables to judge small variations as actual real differences and thus real problems, In that respect cc-ing all injectors at the same time is a better option.

Cheers,

Henk
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Re: WPS500 Pressure transducer back leakage tests

Postby Steve Smith » Wed Jul 23, 2014 12:16 pm

Hello Henk and thank you for the feedback, it is much appreciated and a great theory too.

I will continue to work with the WPS spill testing, but for now have been sidetracked. In the meantime I have dug out a recent spill test I carried out with a Corolla which as luck would have it utilises a steel spill rail into a short reinforced short rubber hose. (approx 70 mm in length)

The WPS was connected directly to this hose and a spill reading taken at idle.

COROLLA SPILL TEST.jpg


What is interesting is the pulsations in the spill rail align just before the trough of the spill waveform!

Again, more research required as any potential expansion of the spill hoses has been eliminated with the above test.

Toyota_Corolla_2001_Diesel_20140723-0001.psdata
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Rest assured this is on my hit list to investigate further and will post accordingly.

Take care.....Steve
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Re: WPS500X Pressure transducer back leakage tests

Postby Budgie » Mon Jul 28, 2014 6:29 pm

As I understand it, a common rail solenoid operated injector uses the spill as an aid to injector opening by allowing rail pressure to lift the pintle off it's seat so that fuel under pressure can be injected. The problem occurs as the internals of the injector wear then rail pressure partially bypasses this process causing excessive back leakage and eventual low rail pressure. I am talking about solenoid controlled injectors but this is further exaggerated with pizo controlled injectors as on VW the injector needs a level of pressure acting against the back leakage to enable operation. Specialist back leakage test equipment is required, but the wps would dispense with such equipment I would guess. I have tried the wps myself on solenoid controlled injectors particularly on the Toyota d4d engine, as access to the injectors whilst engine is running is nigh on impossible. I fit it in the return after it has exited the cylinder head and as mentioned trigger off No. 1 injector and whilst monitoring fuel pressure sensor I have managed to correlate a drop in rail pressure to an injector's increase in spill pressure. ( not my idea but that of a colleague Mark Stammers).
Nice explanation Steve, I have somewhere a capture demonstrating the above and will post in the near future.
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Re: WPS500X Pressure transducer back leakage tests

Postby ianboyle » Mon Jul 28, 2014 7:43 pm

Hi I don't post much but have found this very interesting.

I repair a lot of diesel issues on Cummins engines, particularly the common rail ISB range used on Iveco, Man, Daf etc where the fuel return is a common line drilled into the cylinder head. In this situation the Pressure Transducer test presented before would be very effective as it is not possible to test the return of the individual injections without considerable preparation work. If I can bring myself to afford this fancy product I will probably find myself enthralled in analysing customers waveforms to everyone elses dismay :)

Keep up the good work Steve, I'll be watching closely to your published advancements.
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