Waveform wanted: Faulty diesel injector

[PicoMike]

Hi All,

We are in need of a faulty diesel injector waveform to use in our marketing. We need one to simply show an obvious fault (basically an example of a bad waveform so we can point out the fault).

In a perfect world, a matching good waveform too so we could show the difference.

Sadly, no reward or prize is offered, but you can feel warm and fuzzy inside knowing you have done a good deed for the day

Thanks!

[STC]

Mike

That is a Big Ask !

I have, and for my sins, always have had diesel vehicles around me with Injector faults.

Diesel injectors, unlike conventional petrol counterparts are Indirectly fired making it somewhat more difficult to use current draw as an indicator or an insight to how the mechanical components are behaving. The ECU looking at whatever it is looking at (Current - Short to Ground - Open Circuit) will be none the wiser ? Other than Misfire Detection

I doesn't help that the ECU will shut down Injector command (voltage) at the first sign of ELECTRICAL" trouble, (same goes for the newer wheel speed sensors) The window of opportunity is tiny. Possible IF you can catch it in the act.

We would need an Injector that (electrically) breaks down with heat and be able to capture that. It would not be a case of "before & after" more so "Working, Failed & Shut Down"

Using Bosch FSA 050, Megger 410 or similar Insulation testers are the key to highlighting the gremlins in these.

Steve Smith has done some work analysing FRP reaction, Accelerometer on the delivery pipes at the point of Injector firing, WPS on Leak Off for that very reason, showing a bad/failing injector(s). I may be wrong and happy to be corrected but that may be the best you can get. At your end of the table, from a marketing point of view, you would be doing well to find better reasons to buy a Pico, WPS & NVH all in one hit

If the vehicle is fitted with Pressure Sensing Glow Plugs then that could be an avenue to explore. Again it doesn't directly answer your question.

on Page 4 of this thread topic12911-30.html you can see a faulty Diesel Injector In Cylinder 3 and then a Good Injector in Cylinder 3. When that vehicle is eventually fixed a known good capture will be published completing the Set - so to speak.

The downside of that is that the pre requisites of that test are confirming timing, good compression and swapping injectors. The engine must be able to run autonomously, which would be of little use to a man staring at a non runner suspecting multiple injector failure.

[Joller79]

What about a glogged up injector, it could have a longer activating period, but that would be it.

[victor2k]

Hello,
For faulty injector searching you can use a accelerometer and a clampmeter.
I made some registrations on a working LC120 :the accelerometer will see to you the opening of nozzle and the clampmeter will see you the activation of injector.
I used a Pico 4423,a clamp connected to chanell a,a(home made) mma7361 accelerometer connected to channel b
As you can see in the attached file with red is a opening(or closing?) noise of nozzle
Regards

[victor2k]

Also you can use the same setup to find a knocking injector but the closer cylinder will give you a stronger noise ...and I don't know what corection factors must be applied.
In the attached file you can see a good working 1KD engine(withuot knocking) with cil 1 activation as a reference.
Maybe someone can tell us more about corection factors?Acceleration sensors(home made or genuine) or distance and transmission factor of cylinder head will modify corection factor?

[steevegt]

Hi there Myke

This is my first post in here, so I hope to be helpful to this thread.

One time, one of my cars, an 2008 Opel/Vauxhall H 1.7 cdti (Denso system) develop a knocking noise at idle.
Injector fault was my first thought, but that needed to be confirmed...

So, my first try was to look at injector return line pressure, and see if something was out of the ordinary.
According to what I know about this test, it may not be very conclusive in some cases, but If I saw perfect even pulses, I moved my direction to a mechanical problem.

So first channel (Blue), I used the Fluke PV350 connected to the injectors return line.
Second channel (Red), I used the Pico 60 Amp Clamp connected to the first injector, for synchronization purposes only (at least for now). All the following captures were made at idle.

Common rail injector 1, return line pressure

*Sorry but Pico software is in Portuguese... Pressure is badly written also...

So, my injector fault looks a little more plausible now! We can see very clearly (red circles) that we have a pressure peak in the return line, most likely at the same time of an injection event. The peak was always present, and the shape of the waveform, for all 4 injectors is very consistent, as we can see.
The firing order of the engine is 1-3-4-2, so it looks like we may have the injector 4 at fault...

I moved the amp clamp to the number 4 injector, in hopping to see if something was odd in the current waveform, maybe... It could be a solenoid fault, as far as I know...

Common rail injector 4, return line pressure (zoom)

The waveform shape looks ok, but the time width of the pilot injection does look odd...

Common rail injector 4, pilot injection time (bad)

Common rail injector 4, main injection time (bad)

We can see that the main injection event is even smaller that the pilot injection. This is something that does not look right at all... I believe that this must be related to some dynamic adjustment of the engine computer module to that injector, trying to compensate for the hydraulic malfunction. There were no codes in memory by the way.

The injector number 1, pilot and main injection had a very different time width. The difference is visible in the picture.

Common rail injector 1, main injection time (good)

Replacing the injector was the next move. The following captures were made after the injector was replaced.

Common rail injector 4, return line pressure (new inj)

First of all the engine knocking noise was over, so this was a fix.

The return pressure still has a slight pressure peak in injector 4, but much lower than the one it had before. The other 3 injectors have some high millage already (> 185k miles), so I believe that a slight difference may be normal in this test... We also don't have bottom peaks like the ones in yellow, that were present in the first capture.

Common rail injector 4, main injection time (new inj)

The main injection timing event is normal again.

So, even if the waveform at first glance looks good, the relative time width of the injection events may indicate a problem. I believe we can call this example a faulty diesel injector waveform.

[STC]

would I be right or wrong in suggesting that this particular fault could be seen in serial diagnostic data - Smooth running values ??

What you show is more ECU control of the Injector over any evidence that it has a fault. Low Compression in one cylinder etc etc would give similar bad results ??

Just as smooth running values don't point to an injector fault but every aspect of said cylinder ?

[steevegt]

In this particular system there is no serial data that shows this.
You only have data (angle and main injection time I believe) for number 1 cylinder. So, as far as I know, scoping the injector control was the only way to know that the ECU was doing this...

But your right, at first glance the ECU could be doing this for anything that could cause a power difference in that cylinder, not just an injector fault.
I remember I did a relative compression test back then, with that thought in mind, and all cylinders where really good. The minimum was like 98% from each other if I remember correctly.

The thing is that, in this case, the ECU is commanding the main injection event to be open less time than normal, so it is trying to reduce power (fuel) on that cylinder. I'm I right? Isn't this evidence of an injector problem? What else could cause this behavior from the ECU, or a higher than normal power from one particular cylinder?

By the way, shortening the main injection event, in a functional injector, shouldn't this translate into a relative lower pressure peak in the return line? The opposite was present. I'm not so sure about this second effect, but I believe it is plausible to assume it will, giving more evidence of an injector problem...

[STC]

But your right, at first glance the ECU could be doing this for anything that could cause a power difference in that cylinder, not just an injector fault.

And if that is the case, then the "Improvement" you show in the before and after captures just happens to be (in this case) rectified by replacing the injector. Everyone is happy

The curve ball being that a different fault in that cylinder, and subsequent rectification could possibly give similar before and after captures. Hence I argue that there is no easy way to spot a bad injector, or more accurately bad injection from a waveform (Electrical failure of the injector / fault evident by leak back analysis aside)

Exhaust gas analysis with the manifold removed, isolating each cylinder still would not be conclusive. Again, too many variables in there

The eyes of the ECU extend only as far as the CKP, its ability to measure the speed and rate of increase of each power stroke and then take corrective actions to keep it even & smooth.

Without doubt you have done some great work capturing the waveforms above and shared them with the community here. So, not wishing to be argumentative, same as you I too am in pursuit of a definitive way to pick out a Diesel injector at fault. from what I have encountered, there are just too many variables to achieve that.

The best I have ever achieved is to move the injector to a different hole and watch the fault move with it or not.
Second best is using extensive best endeavours to rule everything else out and take a chance with a new one.

I read some place that fuelling a modern day diesel engine efficiently is possibly one of the most complex processes known / achieved by man. The fact that we have to code them is clear evidence that they cannot make two injectors the same (or is that a money thing) In that case how can we apply the same test to all of them.

For sure the ECU will treat and fire all injectors in a particular engine differently, dependant on each calibration code stored with in it, further throwing a spanner in the debate of how to conclusively condemn or confirm an injector with a scope.

[steevegt]

And if that is the case, then the "Improvement" you show in the before and after captures just happens to be (in this case) rectified by replacing the injector. Everyone is happy

The curve ball being that a different fault in that cylinder, and subsequent rectification could possibly give similar before and after captures. Hence I argue that there is no easy way to spot a bad injector, or more accurately bad injection from a waveform (Electrical failure of the injector / fault evident by leak back analysis aside)
...

I assume I don't prove my point, in a very good way, in the first post, but I believe that I made a good argument after that.

The scope capture of the current waveform of this injector, proves that cylinder number 4 is running with too much fuel, being this the only way I can think of, that a cylinder could produce too much power.
I don't believe that the calibration parameters of this injector is a realistic variable here, because the main injection event is even shorter than the pilots! This is very extreme, and never seen that on any waveform.

What else in the cylinder could possible cause this, except for an injector problem, delivering too much fuel?

I don't have a guess for this, that is not unlikely.
Could the extra fuel be oil in the cylinder? Fed in a very regular and constant way, not revving the engine? I really don't think so...
Could the pilots be way too long, delivering too much fuel in the cylinder, causing the ECU to shorten the main injection event? Maybe, but this means that the calibration parameters are unfitted for that injector, pointing to an injector problem once more...