WPS500X Pressure transducer back leakage tests

Ask for and share advice on using the PicoScope kit to fix vehicles here.

Re: WPS500X Pressure transducer back leakage tests

Postby Steve Smith » Tue Jul 29, 2014 12:47 pm

Hello again and thank you for all the input and feedback.

It would be good to see other tests posted here as we can start to pick the bones out of how different spill formations vary from vehicle to vehicle.

Returning to the vehicle in my original post, we decided not only to introduce a misfire but to monitor the hydraulic activity inside No.1 injector pipe using an accelerometer.

Here we could now monitor the relationship between activities within the back leakage circuit, common rail and No.1 injector pipe, whilst utilising No.1 injector as a sync.

The results are compelling and make for interesting assumptions when analysing spill pressure.

During our analysis we did notice how the spill peak of No.4 Injector could present an issue in the near future given the odd peak formation that was not present on our original test. (Remember this is the same vehicle revisited for further testing)

NO MISFIRE 20 MS DIV.jpg


Moving onto the pressure events themselves, we can see how each activity relates to another as we would appear to have all avenues covered.

The image below displays our vehicle with a misfire on No.3 Cylinder. (Injector harness disconnected and installed into a load box).

MISFIRE 50 MS DIV.jpg


The effect of the induced voltage into the common rail pressure signal is immediately apparent with a reduction in the peak voltage during the injection event, accompanied with a disruption to the formation of the pulsations, given No.3 injector is no longer dispensing.

Moving onto the spill waveform, the initial opening of injectors No.1 and No.2 is met with an increase in spill pressure as expected.

What is interesting, the initial opening of N. 4 injector is not met with an increase in spill, which may tie up with the odd peaks we can see after No.4 injection event. (Another possible early warning for No.4 injector)

If the events surrounding No.4 injector were interesting, the fact we have an increase in spill pressure during the initial opening of No.3 injector is just plain odd, given No. 3 injector is not connected! Any theories are more than welcome here?
(Possible spill weep via No.3 injector given the rail pressure has not dropped during the missing No.3 injection event)

Finally, the accelerometer mounted on No.1 injector pipe (High pressure) reveals activity during and after the injection event along with other events from neighbouring injectors.

Remember, although the accelerometer is sensing events in No.1 injector pipe, this same pipe is connected to the common rail, so allowing the accelerometer to sense all events linked to all injection pulsations with an increased amplitude for events in No.1 injector pipe (Simply because of the mounting point of the accelerometer)

What we can conclude from the attached image is as follows: (No.1 injector only)

1. The Initial opening of the injector is met with an induced voltage into the fuel rail pressure sensor signal accompanied with a decrease in common rail pressure.

2. The initial opening of the injector is met with an increase in spill pressure followed by a drop, then an immediate peak relevant to the recovery of common rail pressure after injection (See 3 below). Therefore the large peaks we see in the spill rail occur after injection (between injection events)

3. Activity seen by the accelerometer indicate large pulsations after the injection event. As the pulsations subside, the spill pressure reaches its peak.

MISFIRE 50 MS DIV.psdata
(2.6 MiB) Downloaded 181 times


I hope this information is of some value and can be compared against other vehicles which I have no doubt will differ from system to system.

The use of the accelerometer in this test has highlighted the use of yet another non-intrusive technique when making an initial assessment during the golden hour!

Take care…….Steve
Steve Smith
Pico Staff Member
Pico Staff Member
 
Posts: 442
Joined: Sun Aug 25, 2013 7:22 am

Re: WPS500X Pressure transducer back leakage tests

Postby tode » Tue Jul 29, 2014 8:08 pm

Very interesting these tests and I also agree on the fact that for any system changes the response of the system, the injector type, the length of the tube back, the presence of pressure regulators, if you use HP pump with 3 pistons, the variables increase if pumps are used in one or two pistons (Bosch CP4), where the pressures in the rail are very undulating, or returns in pressure (eg 10 bar) or return circuits in depression as plants Delphi where in recent models, the engine control unit uses small commands to calibrate the pressure at the injector rail, through the circuit back .....
Thanks Steve, here teamwork can be of great help to highlight special features.
tode
User
User
 
Posts: 42
Joined: Fri Jun 20, 2014 6:59 pm

Re: WPS500 Pressure transducer back leakage tests

Postby HC_CDC » Fri Aug 01, 2014 1:27 pm

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

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

Take care.....Steve


Thanks Steve, not what I expected and still no explanation why this shows up in this manner. I'll keep following this thread to see if anything new shows up. In theory the moment the pilot valve lifts the control pressure should discharge to the measured space and therefore increase the pressure there momentarily. I assume you have vented the measuring connection all the way to the WPS sensor, maybe even the sensor itself (will be fiddly) any air in that space will also delay the pulse significantly.

Henk
HC_CDC
User
User
 
Posts: 19
Joined: Wed Jul 31, 2013 3:11 pm

Re: WPS500X Pressure transducer back leakage tests

Postby Steve Smith » Mon Aug 04, 2014 7:55 am

Hello Henk and thanks for the feedback.

I agree with the "Theory" Henk as you have mentioned and of course would welcome more spill patterns using the WPS so as to build a portfolio.(Waveform Library would be ideal)

It would be very interesting to see how the "theory" holds up between differing vehicles and systems too.

The spill pattern on first connection will look odd until (as you have mentioned ) the device is bled.

Using both the Corolla and the Merc, this was relatively simple using either the "pressure increase feature" or numerous WOT (wide open throttle) events to purge any air from the test equipment.

Monitoring back leakage from the WPS to the collection bottle accompanied by the formation of the correct waveform after bleeding, confirms the bleed process to be successful.

During the tests, any air present can be detected in the return spill line to the collection bottle and displayed on the scope screen as "odd formations". Monitoring in this fashion ensures the introduction of air during a test (via low fuel level for example) will not send you off on a wild Goose chase.

It is always good practice to assume that any anomalies we identify when testing is as a result of our test equipment or settings until you can prove otherwise.

Keeping this is mind will only increase confidence for you and your customer when you do find a real error/glitch in any waveform.

I hope this helps and any waveform additions here will help to build our collective knowledge

Take care......Steve
Steve Smith
Pico Staff Member
Pico Staff Member
 
Posts: 442
Joined: Sun Aug 25, 2013 7:22 am

Re: WPS500X Pressure transducer back leakage tests

Postby busjockey » Sat Mar 28, 2015 9:45 pm

Steve that is very cool! I will have to try this myself, I could use this to identify leaking injectors! I will share when I get the tests done. Thanks for all the effort!
busjockey
User
User
 
Posts: 17
Joined: Mon Jun 09, 2014 1:34 am

Re: WPS500X Pressure transducer back leakage tests

Postby Steve Smith » Tue Mar 31, 2015 2:09 pm

That would be great, any feedback is always welcome, even if you feel it did or did not work as we can only discover the limitations when we test multiple vehicles

A couple of tips:

Keep the spill line/hose to the WPS short

Ensure the hose cannot expand (rigid enough for the pressure involved)

Ensure we have all the air bled from the WPS.
We have found momentarily holding the WPS upside down can remove additional trapped air from the WPS measurement chamber

I hope this helps...take care.......Steve
Steve Smith
Pico Staff Member
Pico Staff Member
 
Posts: 442
Joined: Sun Aug 25, 2013 7:22 am

Re: WPS500X Pressure transducer back leakage tests

Postby tode » Thu Apr 02, 2015 9:42 pm

Hello Steve, as you have reported is a test "delicate" and easy to get wrong reading, a question:
Why connect the WPS in series with the bleed screw open and connect the sensor with T-fitting, drain well measuring chamber and then let drain closed?
The measure is not real?
Leaving open the bleed screw does not alter the pressure in the circuit of the return, as in the case of installations delphi (depression) or new Bosch Piezo (pressure)?
Greetings.
tode
User
User
 
Posts: 42
Joined: Fri Jun 20, 2014 6:59 pm

Re: WPS500X Pressure transducer back leakage tests

Postby hbr » Tue Feb 02, 2016 8:40 pm

Hello I was wondering if someone has a answer to the question from the post above?
I ask myself the same question why don't t in the wps in the circuit?

Kind regards.
hbr
Advanced User
Advanced User
 
Posts: 54
Joined: Tue Nov 08, 2011 10:15 pm

Re: WPS500X Pressure transducer back leakage tests

Postby Steve Smith » Fri Feb 05, 2016 4:47 pm

Hello and thank you for the continued feedback and sorry for the late reply Tode

Tode and HBR please forgive me here as I do not fully understand the questions regarding connectivity of the WPS for this test.

I have included an image below as this may help with clarification;

Spill test_extended.jpg


Does this help or would you like to see the pressure transducer inserted into the return line?

Assuming the pressure transducer bleed was held open, this too would reveal pulsations from each injector but would not allow for a cumulative volume measurement of back leakage.

I would like to try it though and will now add it to the list.

Thank you for the prompt on Todes question HBR. take care.......Steve
Steve Smith
Pico Staff Member
Pico Staff Member
 
Posts: 442
Joined: Sun Aug 25, 2013 7:22 am

Re: WPS500X Pressure transducer back leakage tests

Postby hbr » Fri Feb 05, 2016 7:54 pm

Hello Steve,

I and I suppose Tode mean why do you put the wps in line in the circuit, the flow now goes trough the wps,
why don't U use a t fitting in the return line and leave the system as it is?

Kind regards HBR.
Spill test.jpg
Spill test.jpg (43.53 KiB) Viewed 884 times
hbr
Advanced User
Advanced User
 
Posts: 54
Joined: Tue Nov 08, 2011 10:15 pm

PreviousNext

Return to Diagnostic discussion

Who is online

Users browsing this forum: No registered users and 1 guest