Jaguar S-Type 2.7D with hesitation at idle

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Jaguar S-Type 2.7D with hesitation at idle

Postby aux_r » Thu Jul 04, 2013 5:26 pm

Jaguar S-Type 2.7D with hesitation at idle. No DTCs registered. Engine’s behavior suggests a problem with one or some injectors. So we decided to test the injection using the scope to confirm and identify the fault injectors.

With engine running at idle condition, we measured the injection pulses in voltage and current from injector 1, which will be our reference. This provides us one tool to analyze a possible fault with piezo crystal. We used the waveform reference function of Picoscope 6 with the waveform of this injector and measured the rest to compare with it.
Injector1_01.jpg
Injector’s 1 waveform, taken as reference. The voltage measured at injector positive, this is shared with the other 2 from the same bank, the trigger adjustment is taken in the current waveform by this reason.

The state of piezo actuators of all injectors is right: Current rises similar values in all of them and voltage slopes and values too. Notice the quantity of energy charge and discharge are equal (See the asymmetrical shape from current waveform).
Injector2.jpg
Injectors 2, 3 and 5 have similar times of pre-injection and main injection and similar times between both.

Notice main injection time of injectors 1 and 6 is greater than others.
Injector6.jpg
Main injection time from injector 6 is even greater than the one from injector 1.

Injector 4 has the same time of injection than 2, 3 and 5, but a great time between injections.
Injector4.jpg
Time between injections from injector 4 greater than the one from the others

Fuel pump is radial type with three pumping elements evenly offset at an angle of 120 degrees. This generates a flat pressure which simplifies the process to analyze the hydraulic work of injectors seeing the drop in pressure after the activation of each injector. To see this effect, measure the signal from rail pressure sensor in AC mode, adjust the scope at lowest voltage scale and use the required level of filtering.

Taking injector 1 as reference we can identify the effect on pressure of each injector. The picture shows injector 1 activation didn’t get a drop in pressure. This spot an issue with this injector.
Pressure drop_retoc.jpg
Effect on the pressure of each injector. Reference: injector 1

Also, the drop in pressure from injectors 4 and 6 is lower than the rest of the others. May injector 1 bring about an idle compensation effect from ECU? Let’s see, main injection from injector 6 is the longest one, but drop in pressure is lower than the ones from injectors 2, 5 and 3. This injector doesn’t seem to be right too.

Injection time from injector 4 are similar to 2, 5 and 3, but the time between pre-injection and main injection are greater than the rest. This seems an effect of cylinder 1 compensation. We take the decision to change injectors 1 and 6, solving the problem. Now the engine runs smoothly. All the injector times are similar and its effect on rail pressure too.
Pressure drop repaired injectors.jpg
Effect on the pressure after changing injector 1 and 6.
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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby Robski » Thu Jul 04, 2013 10:28 pm

Nice approach on AC coupling the FRP sensor. I'm not sure you would get 100% even drops because of the distance of an injector from the FRP sensor, i would imagine the effect would be similar as using the FLS on a FPR on a petrol ' V ' engine, however if the rail is central to all the injectors they may be pretty close especially the two opposing each other as they would be the same distance & should pretty much match.

I can see where you are coming from with the voltage & current captures for the Piezo side of the injector BUT the injection corrections (smooth running values) have to be taken into account for the opening times, maybe lifting off idle away from the smooth running strategy may have been of diagnostic value of opening times ?
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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby Valhalla » Thu Jul 04, 2013 11:30 pm

I agree with Robski about nice use of FRP sensor information. This have given me an idea for the Vivaro problem that still lurks somewhere in my schedule (if I get to work on it again...) and is something else to back-up a physical spill-return volumetric test for each injector on the fuel system. There is a pattern in diagnostic technique appearing with AC-coupling of various (and seemingly random) engine sensors that yields lots of information in a few minutes for relative cylinder checks.

The cylinder balance function on the SID201 SVDO strategy is a bit flakey on the early Jags, so I definitely wouldn't pin too much hope on injection durations on their own (ie. without taking into account the pressure drops for each cylinder on the FRP). Even away from idle, the strategy is still active for a significant speed/load proportion of engine running (both open and closed-loop) so the results could shift from test to test. Post 2007 TDV6 engines have got this sorted a lot better, reading back calibration methodology from the Landrover engines that nailed this for SID204.
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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby Fat Freddy » Fri Jul 05, 2013 2:33 am

Just a question. Not too good on CRD.

Can this pressure drop shown here be attributed to the injector? It seems to occur over a large amount of crank degrees where most of the time the injector is closed.

What does it look like with less filtering?

This image is similar but not consistant, which is why I'm confused. :?

Filtered.gif


Less filtering.

Reduced filtering and SCV.gif



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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby Valhalla » Fri Jul 05, 2013 11:28 pm

Fat Freddy wrote:Can this pressure drop shown here be attributed to the injector? It seems to occur over a large amount of crank degrees where most of the time the injector is closed.
FF


Yes, the pressure drop is inevitable on each injection, as the injection itself will consist of a finite volume of fuel that has to be replenished with the HP pumping elements. As these elements are running at a fixed volume on this engine at idle, which is less than the injected quantity (for fuel economy reasons, the HP pump does not try to immediately compensate for the volume injected on the first one or two strokes of the pump after each injection) what you end up with is a sawtooth pressure. Or that is the theory, if you apply enough filtering to overcome the HP pump pressure fluctuations and other standing-waves in the main rail. The pressure drops suddenly as each delivery line to the injectors is purged of fuel, then there is a gradual rise as the HP pump catches-up. The HP pump runs in open-loop control for the VCV (volume control valve) on this engine for most of the time - whatever the Marketing guys say!!, and the mapping for this is based on the injected quantity as well as engine speed.

Robski's point about the lengths of the lines between the main rail and the injectors is a valid one; cyls. 1 and 6 are always the first to give trouble, being as they are disposed at the front left and rear right of the TDV6 engine as viewed from the front of the car.
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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby Fat Freddy » Sat Jul 06, 2013 8:10 am


Yes, the pressure drop is inevitable on each injection, as the injection itself will consist of a finite volume of fuel that has to be replenished with the HP pumping elements. As these elements are running at a fixed volume on this engine at idle, which is less than the injected quantity (for fuel economy reasons, the HP pump does not try to immediately compensate for the volume injected on the first one or two strokes of the pump after each injection) what you end up with is a sawtooth pressure. Or that is the theory, if you apply enough filtering to overcome the HP pump pressure fluctuations and other standing-waves in the main rail. The pressure drops suddenly as each delivery line to the injectors is purged of fuel, then there is a gradual rise as the HP pump catches-up.


Thats kind of what I'm saying. But not what's being shown The pressure is continually falling after the injector closes.
(If you check out the images it's several degrees and milliseconds).

The HP pump runs in open-loop control for the VCV (volume control valve) on this engine for most of the time - whatever the Marketing guys say!!, and the mapping for this is based on the injected quantity as well as engine speed.


I don't know the system at all so my answers are kind of limited.

But... Another point I noticed today
- Image 5 from the OP. You can clearly see injector 2 firing but this appears to be about 2/3's of the way down the slope (It does mark out in degree's). Later in the same image injector 3 fires but this is at the top of a slope.
There is a far bigger drop post 3 injection compared to 2. Too much differance. :roll:

In my opinion, to much data has been filtered out. I have no doubts those dips exist but what they are I don't know. I need to find out more on this sytem.
As I said earlier, it would be interesting to see the image with less filter.

Here's one with less filtering - Possibly showing a drop. Hard to say. But under load it definatly appeared that way.

in.gif
FRP, Injector, SCV


Whats your thoughts?


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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby Robski » Sat Jul 06, 2013 11:06 am

In my opinion, to much data has been filtered out

it would be interesting to see the image with less filter

My thoughts too ..............
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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby aux_r » Sat Jul 06, 2013 1:59 pm

Thank's for all comments, I agree with most of the points of view of Valhalla about this case of study.
I would like to comment my point of view about some of the questions and topics exposed here trying to clarify the images showed by Fat Freddy.
First of all it's known the type of HP pump. In the case of study I've exposed is a radial pump with three elements, if all its elements (and valves) are right, the pump delivers a flat pressure.
As I see the images by Fat Freddy, the injection pulse is measured in negative side and we can see the pulse of all four injectors in the image.
Filtered retoc.jpg

The main wave we can see in this image is a combination of two harmonics: one with a frequency of one per engine's revolution (blue), and the other at the frequency of injection (green). About the main harmonic (blue) we must know the type of pump because if it is a pump with one or two elements as CP4 (Bosch) or DFP1, DFP3.3 or DFP3.4 (Delphi) for example the generation of pressure creates this kind of harmonic.
In some cases if a valve of one pump's element doesn't open/close the pump creates this kind of harmonic but greater in amplitude if an element is completely canceled, as you can see in many CP1 pumps at partial load. Another thing is knowing if the main harmonic is stationary.
Also problems in delivery line or particles in the DRV or HPV can cause something similar as an effect of the pressure compensation.

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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby Fat Freddy » Sun Jul 07, 2013 8:09 am

Thanks aux_r for the explanation. It fits in and explains the rest of my capture very well. It is a Denso HP3 pump which as far as I know (diesel dumb) has two pumping elements. It gives me alot better understanding of what I am seeing.

I did have a look at another file from a Chrysler 300C, which is a Bosch CP3 (Mercedes?) and appears to use three elements. The rail pressure was a lot more stable, no matter how I manipulated the capture. Unfortunatly I couldn't see any injector drops although it was only a DC capture.

I think there is something in using the AC coupling but I'm not sure I would (not that I see much diesel) pin an injector on it yet. Mainly because of the inconsistant pressure dropping pre and post injection.
Also the drop on injector one is still minimal compared to say three.
Although it is certainly something to bear in mind in future.


Thankyou.
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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby Valhalla » Mon Jul 08, 2013 11:18 pm

aux_r wrote:The main wave we can see in this image is a combination of two harmonics: one with a frequency of one per engine's revolution (blue), and the other at the frequency of injection (green). About the main harmonic (blue) we must know the type of pump because if it is a pump with one or two elements as CP4 (Bosch) or DFP1, DFP3.3 or DFP3.4 (Delphi) for example the generation of pressure creates this kind of harmonic.


Remembering, of course, that the first rule of Diesel injection HP pump design is to drive it at a ratio that does not match the camshaft or crankshaft, for the very reason your example shows above!
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