In cylinder pressure waveform "blip"

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Re: In cylinder pressure waveform "blip"

Postby STC » Tue Nov 01, 2016 3:30 am

The whole reason for starting this thread was to see if someone had any ideas about the "blip",


I'm fairly new to Compression waveforms too, hence I am showing an interest in this thread. Reasonably up to speed with pressures which I hope will help me, in time, to understand them.
Your Piston Slack / Rock theory , I questioned at first, for the same reasons you did.

I'm thinking that the rocking piston would cause the Seal around the Rings to break momentarily and we would get an attempt at equalisation of pressure between the Combustion Chamber and the Crankcase. Assuming crankcase pressure to be near atmospheric (it is a non runner) so that would cause a rapid drop, not an increase ?


Fact is that at the start of the Blip your Cylinder Pressure is 9.3 bar and rises to 9.6 bar. A Ludicrous scenario, I know, but for a momentary break in the Piston Ring Seal to cause that you would first have to have at least 9.6 bar in the Crankcase ?
It gets from 9.3 bar to 9.6 bar in just 1.1ms & then maintains that increased pressure for a further 1ms - That is no walk in the park !! and an excellent achievement without a bang ?
Common sense & the lack of an alternative makes me think that there must be a gaping hole in my knowledge or I am working with a myth that needs to be burst. Eager to learn from this.

I wonder what the pressure transducer in the dipstick tube, synced to the same cylinder as in the original capture will show?
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Re: In cylinder pressure waveform "blip"

Postby victor2k » Tue Nov 01, 2016 12:11 pm

Hello,
You can record in the intake/crankcase/exhaust pressure waveform at the same time with cylinder pressure?
Maybe there is the answer for your question. :roll:
Your engine have oil consumption(you can see this using an endoscope)?Only a liquid(oil in this case) pumpimg in cylinder will give to you a pressure increase.
What volume do you used for your dummy injector adapter?11.6 bar isn't enogh for a engine what have the compression ratio at 1:19

Regards
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Re: In cylinder pressure waveform "blip"

Postby Steve Smith » Tue Nov 01, 2016 3:40 pm

Hello and thank you for the posts, images and waveform as I know they take valuable time to complete.

I am intrigued by the event taking place in the cylinder and have some questions (sorry) if you have time to respond?

Often when we find anomalies it is worth qualifying our measurement.
I have lost count of the times I think I have found something when in fact it was my measurement or technique responsible for the error.

Would it be possible to measure all cylinders in the same fashion?
I would like to know if all cylinders replicate this "Blip"

Can we confirm there is no leak on the measurement equipment. (This is not always audible)

Prior to the engine non start were there any customer complaints of excessive noise or exhaust smoke?

Regarding the measurement hose and dummy injector used, are they clear with no unique integrated valve?

Could we try Pico Diagnostics for an Absolute compression test?
Here we can compensate for the volume of your pressure transducer, hose and dummy injector for a true peak pressure value. Please see topic14971-10.html

As mentioned above, could we add other waveforms into the mix?
I would like to see if this blip is visible in the cranking current peaks (or battery volt drop ((troughs)) during cranking)

Using the reference waveform feature and a trigger from a fixed input, adding Intake Exhaust and Crankcase presures as mentioned above would be ideal

Would it be possible to remeasure via a dummy glow plug? (If applicable and I guess accessible)

The expansion pocket is large for a diesel engine (As deep and low as a petrol engines intake pocket) at -646 mbar

This may or may not be relevant and we should not pursue this without comparing to other cylinders and querying the measurement hose/technique

This leads me onto the exhaust value timing based on the position of the expansion pocket. I have attached an image that should help as I fear the exhaust valve opening event is advanced.

Cylinder waveform.jpg
Cylinder pressure waveform


Remember, the valve timing can be correct at the timing gears but incorrect on individual cylinders

I hope this helps and I am so sorry for all the questions

Take care…….Steve
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Re: In cylinder pressure waveform "blip"

Postby Lion Garage » Tue Nov 01, 2016 4:55 pm

victor2k wrote:Hello,
You can record in the intake/crankcase/exhaust pressure waveform at the same time with cylinder pressure?
Maybe there is the answer for your question. :roll:
Your engine have oil consumption(you can see this using an endoscope)?Only a liquid(oil in this case) pumpimg in cylinder will give to you a pressure increase.
What volume do you used for your dummy injector adapter?11.6 bar isn't enogh for a engine what have the compression ratio at 1:19

Regards


Volume of the injector plus adaptor etc is pretty high, so I think that is probably responsible for the lower pressure. I will try and get some other captures along side this later and see what we get.

Steve.
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Re: In cylinder pressure waveform "blip"

Postby Lion Garage » Tue Nov 01, 2016 5:33 pm

Steve Smith wrote:Hello and thank you for the posts, images and waveform as I know they take valuable time to complete.

No problem.

I am intrigued by the event taking place in the cylinder and have some questions (sorry) if you have time to respond?

I'm intrigued also, I will make time as developing skills and knowledge is always good.

Often when we find anomalies it is worth qualifying our measurement.
I have lost count of the times I think I have found something when in fact it was my measurement or technique responsible for the error.

Yep, been there too many times.

Would it be possible to measure all cylinders in the same fashion?
I would like to know if all cylinders replicate this "Blip"

Can we confirm there is no leak on the measurement equipment. (This is not always audible)

Prior to the engine non start were there any customer complaints of excessive noise or exhaust smoke?

Regarding the measurement hose and dummy injector used, are they clear with no unique integrated valve?

OK, I can try and measure all cylinders. I'm a little concerned as the injector was pretty tight in this cylinder. As things stand at the moment I'm leaning towards a cam timing issue (keyway issue??) so in the normal course of diagnostics I wouldn't need to remove injectors. Obviously as they are tight I'm a bit nervous about causing issues removing an injector that I cant justify was necessary for the diagnostic procedure. However, I really would like some more idea what is going on, so If I can get them out to try other cylinders, I will.

I'm 95% sure there is no leak.

No issues with smoke, it doesn't sound great, but I wouldn't say there was excessive noise last time I was in the car. It doesn't use oil.

I've taken the valve out of the dummy injector, the only possible restriction would be the quick coupling on the WPS and a similar style coupling on the sykes compression test adaptor.




Could we try Pico Diagnostics for an Absolute compression test?
Here we can compensate for the volume of your pressure transducer, hose and dummy injector for a true peak pressure value. Please see topic14971-10.html

we can, working out an accurate volume may be tricky. May have to find a syringe or something to work that out.

As mentioned above, could we add other waveforms into the mix?
I would like to see if this blip is visible in the cranking current peaks (or battery volt drop ((troughs)) during cranking)

Yep, will do.

Using the reference waveform feature and a trigger from a fixed input, adding Intake Exhaust and Crankcase presures as mentioned above would be ideal

Yep, I assume you mean use the "in cylinder waveform" as a reference then overlay the other pressure waveforms. May be difficult to keep cranking speed constant enough.

Would it be possible to remeasure via a dummy glow plug? (If applicable and I guess accessible)

Nope, I tried that first, The fuel rail is in the way so I'm pretty sure the connector wont go on, I gave it a try anyway, but didn't like the feel of the glow plugs.

The expansion pocket is large for a diesel engine (As deep and low as a petrol engines intake pocket) at -646 mbar

That's beyond my knowledge at the moment, I have a lot to learn on this subject

This may or may not be relevant and we should not pursue this without comparing to other cylinders and querying the measurement hose/technique

This leads me onto the exhaust value timing based on the position of the expansion pocket. I have attached an image that should help as I fear the exhaust valve opening event is advanced.

Ah haaaa.......now this is where I'm unsure. Using what I would say are the standard timing checks which are widely documented, this does look advanced for Exhaust opening and exhaust closing/inlet opening (when I restricted intake). However, I've spent quite a lot of time looking fault free cars and none of them look correct using these checks, despite cam timing being OK. I have come to the conclusion there are too many variable to check timing using a standard set of values. The only way to be sure is to use a known good waveform from the exact same variant of engine. I've spoken with other people who have come to the same conclusion. However, I now contradict myself by saying, I do feel the the issue with this car is cam timing, I just don't trust the "in cylinder" test without a known good.

Cylinder waveform.jpg


Remember, the valve timing can be correct at the timing gears but incorrect on individual cylinders

Yep, which is what I think the issue could be. I just need to get back to it. I do now have a Vivaro van here with an F9Q engine, so if I get chance, I may grab an in cylinder capture from that!

I hope this helps and I am so sorry for all the questions

Thanks for the input, much appreciated.

Take care…….Steve
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Re: In cylinder pressure waveform "blip"

Postby victor2k » Tue Nov 01, 2016 5:56 pm

Lion Garage wrote:
victor2k wrote:Hello,
You can record in the intake/crankcase/exhaust pressure waveform at the same time with cylinder pressure?
Maybe there is the answer for your question. :roll:
Your engine have oil consumption(you can see this using an endoscope)?Only a liquid(oil in this case) pumpimg in cylinder will give to you a pressure increase.
What volume do you used for your dummy injector adapter?11.6 bar isn't enogh for a engine what have the compression ratio at 1:19

Regards


Volume of the injector plus adaptor etc is pretty high, so I think that is probably responsible for the lower pressure. I will try and get some other captures along side this later and see what we get.

Steve.

Hello,
Maybe your intake is closed by intake shutter.
This will explain the low compression and the great vacuum.
I use a 5-10 ml syringe and motor oil to find the volume for compensation for any new adapter then I put in math :wink:
Regards
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Re: In cylinder pressure waveform "blip"

Postby Lion Garage » Tue Nov 01, 2016 7:01 pm

victor2k wrote:
Lion Garage wrote:
victor2k wrote:Hello,
You can record in the intake/crankcase/exhaust pressure waveform at the same time with cylinder pressure?
Maybe there is the answer for your question. :roll:
Your engine have oil consumption(you can see this using an endoscope)?Only a liquid(oil in this case) pumpimg in cylinder will give to you a pressure increase.
What volume do you used for your dummy injector adapter?11.6 bar isn't enogh for a engine what have the compression ratio at 1:19

Regards


Volume of the injector plus adaptor etc is pretty high, so I think that is probably responsible for the lower pressure. I will try and get some other captures along side this later and see what we get.

Steve.

Hello,
Maybe your intake is closed by intake shutter.
This will explain the low compression and the great vacuum.
I use a 5-10 ml syringe and motor oil to find the volume for compensation for any new adapter then I put in math :wink:
Regards


Intake is clear, no restriction. I did briefly pull the flap closed with a mity vac so I could see the intake part of the waveform more clearly.
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Re: In cylinder pressure waveform "blip"

Postby Dave Hill » Tue Nov 01, 2016 10:40 pm

Hi Steve

I noticed that the psdata file that you shared in your second post, does not look like the same capture as the one in your first post. The injector current events are different.

Or have I mistook something? (quite likely)
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Re: In cylinder pressure waveform "blip"

Postby Lion Garage » Wed Nov 02, 2016 8:24 am

Dave Hill wrote:Hi Steve

I noticed that the psdata file that you shared in your second post, does not look like the same capture as the one in your first post. The injector current events are different.

Or have I mistook something? (quite likely)



Nope, you are quite right Dave.

The first one was a mistake on my part, I'd blanked the injector outlets on the fuel rail when I fitted the WPS, and then tried the WPS capture while in a hurry between jobs on Friday. I then spotted the lack of true injection events which was odd as they were there earlier. The part I was waiting for turned up so I got on with the job I should have been doing and left this. The following day (I think) I needed the bay so pushed the car out, I spotted a pool of diesel on the floor and realised, in my haste I had not tightened the blanks properly, so no fuel pressure = no injection event. Everything was still in place so I just tightened the blanks and re did the capture, complete with injection events.

Multi tasking fail!

Cheers.
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