Sporadic leaking injector while driving.

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Julius Nolin
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Sporadic leaking injector while driving.

Post by Julius Nolin »


About a year ago, a Toyota Avensis diesel came in.

Complaints from vehicle owners:
Sometimes when you drive, the mpg increases to the max and smokes behind the car.
After that, the car returns to its normal position. I checked the car a bit quickly and came to the conclusion that it was one of the injectors that mechanically got stuck when the engine came up in temperature. However, I could not 100% say that this was the case and I sent the car away. :(

Since then i have been wondering if one could use picosope to find out.
My thought was that you could do this:

* Signal/trigger from injector number 1
* Pressure Transducer on the fuel pipe before the high pressure pump.

With these two values, you should be able to see if an injector is mechanically fixed for a tenth of a second? Is there anyone here who has done something like that who wants to share their data?
Is there any case study on this?


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Re: Sporadic leaking injector while driving.

Post by leonardorj »

Julio I bet more on tests with a megometer and a bench machine for injector tests. The oscilloscope can test voltage and current. More finding precision only oscilloscope does not solve in my point of view.

Steve Smith
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Re: Sporadic leaking injector while driving.

Post by Steve Smith »

Hello Julius and Leonardorj thank you for the posts

I too have experienced issues with injectors, both Gasoline and Diesel where every test carried out is inconclusive! This is the theme of the following video https://www.youtube.com/watch?v=7jFf32L ... Automotive

Returning to your Avensis, regarding the “smoke”, is this white in color and does the vehicle utilize a 5th injector in the exhaust system? I ask because this device and circuit may be over-looked whilst focusing on the 4 “In-cylinder” injectors

Does the vehicle exhibit misfire characteristics when the fault occurs? (i.e., lumpy/uneven running and excessive vibration)

If so, we are right to focus on injectors, especially if related to load and have the momentary intermittent characteristics you describe

Because of the occasional nature of the fault, I think we can agree that testing will be fruitless until the fault occurs and concede with Leonardorj that Bench Machine testing for injectors is the only way to go

That is not to say you cannot use the scope to capture the fault event.
With 4 channels I would go for:
Crankshaft position sensor
Injector cylinder 1 current
Fuel rail pressure sensor
Gas pedal position sensor

With the above, you can graph the frequency of the crankshaft sensor when the fault occurs. This will give you a glimpse of the offending cylinder based on the firing order using the synchronization signal of injector 1.

Whilst this does not tell you the injector is at fault; it will allow you to focus on the offending cylinder and therefore suspect injector

With your focus now on an offending cylinder we can look at fuel rail pressure (from the Common Rail pressure sensor) for any anomalies in the repetition and uniformity of the acquired signal

All things being equal (and they rarely are) our fuel pressure signal will reveal characteristics relative to the contribution and activation of each injector. If during the misfire (identified in the crank signal) the fuel pressure uniformity changed, we may be able to attribute this event to incorrect mechanical operation of the injector. i.e., for whatever reason, even though the electrical operation of the injector was OK, little or no fuel was injected!

The reason for choosing the gas pedal position as my 4th channel signal was capturing “drivers’ intention”. Graphing the operation of the gas pedal reveals if the driver was accelerating, decelerating or the transition between the two.

The phrase “Tip-in” is given to the point of changing from cruising to light acceleration (e.g. overtaking on a motorway) and this event is often the prime condition where diesel injector “noise” and misfires manifest. This condition will be captured using the Gas Pedal Position sensor accompanied with an increase in fuel pressure, both of which are ideal signals when diagnosing "suspect" injectors

As you can see from above, we have not focused on measuring injector current, voltage or even injector operation via an accelerometer as all tests will pass and be fruitless if the injector failure is due to a mechanical/physical error!

For example: carbon deposits about the face of an injector or a mis-seating pintle will affect flow rate and spray pattern which is essential for efficient combustion across all engine speeds and loads

With that said, using the scope we can categorically eliminate the electrical control side of the injector from our diagnosis along with fuel pressure, engine management and the mechanical integrity of the engine (via MAP/MAF) such as to leave us with only one “prime suspect”. The fuel injector

Below is classic example of the complexities involved when diagnosing mechanical issues with injectors.
Image 1
Image 1
Note above how cylinder 6 is most certainly suffering from “incomplete combustion” resulting in failure of the crankshaft to fully accelerate after injection. This was captured during “Tip-in” where the vehicle exhibited a slight vibration (slight as this was a V6 with incomplete combustion on a single cylinder which is “carried” by the remaining 5)

Note also the fuel pressure signal is inconclusive as we do have repetition and arguably uniformity! Replacing the injectors cured this issue!

I will write about the above vehicle in a case study ASAP which reinforces the challenges we face within this topic

I hope this helps, take care……Steve

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Re: Sporadic leaking injector while driving.

Post by Martinjensen »

Hello Julius.

Since the consumption meter is reading max when the issue occurs, I don't think that the issue could be a sticking injector.

Based upon the information that the calculated consumption increases during the event, the ECU has calculated that the fuel amount is increased.

The ECU would not know if an injector is sticking, and therefore I don't believe that the calculated consumption would increase if an injector got stuck.

Therefore, I lean more towards an input problem, based upon the information given.

I don't know if it applies to that particular car, but there is a bulletin from Toyota regarding White smoke from the exhaust while driving.

The Bulletin mentions new engine management software, and a new A/F (oxygen) sensor
Bulletin number EG-0111T-0910

Regards Martin

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