Diesel injection effects on fuel rail pressure sensor

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Re: Diesel injection effects on fuel rail pressure sensor

Postby Steve Smith » Thu Nov 07, 2013 4:48 pm

Well Taho, you were not wrong when you said "good luck". I have been trying to power a fuel rail pressure sensor on a donor vehicle using a stable 5V supply and earth independent of the ECM to retest the theory. This is not my concern as this is reasonably easy, my concern has been trying to convince the ECM the fuel rail pressure sensor has not been disconnected. Trying to simulate a common rail diesel pressure reading at idle whilst getting round the "disconnection detection" of the ECM is proving to be a nightmare but I will get there and feedback ASAP.
Steve Smith
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Re: Diesel injection effects on fuel rail pressure sensor

Postby Steve Smith » Fri Jun 20, 2014 12:55 pm

Well I know it has been some time, but over the past months I did get to test the theory re the peaks viewed within the common rail pressure signal during the injection event.

The peaks are most certainly down to the effects of noise induced into the rail pressure signal and not a reflection of activity within the common rail.

However, when looking at the common rail pressure (AC coupled) as a "first look" approach over 20 ms/div at idle, if we can see 4 x induced peaks (4 cylinder engine) then we can at least assume the presence of current flow through 4 injectors, rather than equal contribution of diesel injection into each cylinder, so there is some value to these peaks.

In the waveform below I have used a Toyota Avensis running at idle speed whilst monitoring the common rail fuel pressure (AC coupled)

Using the scan tool and "Active test" feature, I have cut the injection for number 2 cylinder in buffer 3 through to 9, buffer 10 has all cylinders contributing and buffer 11 to 15 has number 3 injector cut.


FUEL RAIL PRESSURE.jpg


Using the filter option you can see the effects upon the waveform as the uniformity of the pulsations change dependent upon which injectors are cut or fueling

All things being equal (which often they are not) we should have equal pulsations between cylinders whether it be intake, exhaust, crankcase, or fuel pressure. Looking for repeatable irregularity is key and I do believe this test is another string to your bow when looking for evidence to support further investigations and confirmation to your customers.

Sorry, due to the file size I have had to split the uploads into seperate files. below are 15 buffers split into 3 files.

NUMBER 2 CYL CUT 1-7.psdata
Buffer 1-2 all injectors on-buffers 3-7 number 2 injector cut.
(7.13 MiB) Downloaded 175 times


NUMBER 2 CYL CUT-THEN RESTORE-THEN NO3 CYL CUT 7-11.psdata
Buffer numbers 1-3 number 2 injector cut-buffer 4 all injectors on-buffer 5 number 3 injector cut
(5.1 MiB) Downloaded 168 times


NUMBER 2 CYL CUT-THEN RESTORE-THEN NO3 CYL CUT 11-15.psdata
Buffers 1-5 number 3 injector cut.
(5.1 MiB) Downloaded 144 times
Steve Smith
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Posts: 442
Joined: Sun Aug 25, 2013 7:22 am

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