Service Issues: DPF Soot filter full

[KBB]

Originally Posted by SwissXC90

Check your fuel trim on all 5 cylinders. This will show any cylinder with poor compression. Reason: the ECU will compensate for low power on one cylinder by increasing fuel. Good compression on all cylinders with have fuel trim within the specified limits.
NOTE: you don't need a compression testing kit for this - all you need is VIDA software.

Both of the above can be done with VIDA, just by connecting to the car and running the tests.

Especially the fuel trim test is a good indicator of cylinder compression.

I would disagree with your thoughts that injector fuel factor correction's are used to analyse in cylinder compression are not correct.

This system cannot assess in cylinder compression pressures. The injector fuel factor correction (or smooth running compensation as it is technically referred to) is to apply fine corrections to each injector to maintain correct combustion. This system adjusts the injector dwell or duration during its firing event to take to correct volumetric flow during the service life of the injector, as in time their fine tolerances from when first produce begin to wear out leading to lower than calculated pressures and pressure drops in the injectors upper chamber.

On every injectors firing event the crank sensor measures that cylinders acceleration speed over its first 90 degrees of downward movement on its power stroke, the ECU will compare this to the other cylinders in firing order sequence on that cycle. Those with a lower speed will have a fuel factor correction applied on its next firing event. Later systems are mow using glow plugs with a in-built peizzo pressure sensor to measure actual combustion pressure which has proven to be more accurate then using crank shaft speed.

The only non intrusive way to assess diesel engine cranking compressions is to use a scope and measure cranking amps which will give and indication of weak compression on cylinders that draw lower amps on their compression stroke when compared to the others, this will not give a pressure reading but a relative assessment. This method coupled with a pressure transducer in the dip stick can be used to monitor compression blow by as this increases the crank case pressure, low current draw with a high crank case pressure pulse indicates cylinder sealing issues. The only definitive way to measure the absolute compression is to remove a glow plug and use either a typical analogue gauge or for pressure and valve timing a pressure transducer which when coupled with knowledge of the reading can diagnose cylinder sealing issues, upper cylinder sealing issues such as leaking valves or incorrect valve train timing..

[SwissXC90]

Excellent response.
I am pleased that my comment invoked such a thorough and detailled technical response from you.
I have actually learnt a few things as well...

[KBB]

Happy to be of service.

to take things a little further and staying with the theme of injector facto corrections, as you quite correctly said there is great diagnostic value in looking at those values.

Acceptable injector correction factors that are within 10% of the lowest and highest injector are considered normal running parameters.

Where an injector is showing more of a positive correction factor compared to the rest is and indication of an injector that is moving out of tolerance in terms of its ability to flow the correct pre determined amount of fuel. Those with higher correction values are starting to loose the ability to hold pressure and if you were to measure their leak back rate likely they will be showing more than the rest. That would be the injector that can be responsible for lowering over all fuel rail pressure leading to the inlet metering valve to run at maximum frequency and the pressure control vale to run at minimum frequency on a dual point control system to maintain system pressure.

Live data is a powerful tool when the values are understood and the over all system of operation is understood. Diagnostics is about finding the absence of the normal and the presence of the abnormal

[Hank3944]

Originally Posted by JockinLeeds

Hank. I feel your pain and watching this thread with interest.
My symptoms are pretty much similar.
Been running with filter full messages on/offfor about a year now.. mainly comes on from a high boost acceleration.. i.e overtakes when it goes into limp mode... Thrash the @rse off it and 15 minutes later ... Fine.
Had a force regen last week.. showed cleared. 0g.
Mine seems related to the swirl flap set up.. which is on the list.
I have some extra bits to look into as a result of this thread but I'm not very handy with a spanner...
#dpfbrothers

Hiya mate, yes mines exactly the same, as soon as it gets to temp and you even touch the throttle, soot filter full and reduced power, so annoying... are your swirl flaps operating correctly? You can normally tell if they har broken due to high soot bulid up just by looking....?

[Hank3944]

So vlvo have said that injector 2 & 3 ae leaking.....

Question 1, if it the injector was faulty would this result in a physical leak where you can see the fuel gathering in the injector recesses, surely when you see fuel gathering would it not be the connection to the injector being worn that s causing the leak? Rather than the internals of the injector?

Question 2, can i assume when they say injector 2 & 3 they are numbered sequentially from left to right so no 2 & 3 is 2nd and 3rd from the left?

[Hank3944]

It looks to me like the fuel line connection are wet. So not the fuel line nut but the bit that actually screws into the injector that connects to the fuel line. Is it worth removing and sealing the thread somehow? Could this give a leaky injector reading?

[KBB]

They seal by compression, may have been loosened slightly when disconnecting the high pressure feed pipe. Not uncommon for injector bodies to leak, often the onset of internal pressure loss.

[Hank3944]

I am trying to work out whether i need to change the injectors or just dsconnect the fuel lines and try and tighten the nut on the top of the injectors and connect again......?

[4x4]

I decided to check my DPF soot mass this evening when I returned home so connected it up to Vida. I had no idea what to expect but as it is a one owner car with full service history I did hope it would be all good. I know roughly where the car travelled to/from every day so I know it wouldn't have been sitting in too much traffic getting clogged up with soot

[colinbos]

Nice and low.

Of course, this goes up and down with use. I have had VIDA connected to the car when my DPF mass was 19g and during a dual carriage way run, I saw the mass reduce before my eyes, going to near Zero after 30mins.

Great tool.