In cylinder pressure waveform "blip"

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In cylinder pressure waveform "blip"

Postby Lion Garage » Mon Oct 31, 2016 11:02 am

Morning guys.

Ive been a member for many years but had completely forgotten about the Pico forum, I just stumbled across it while looking at their website. So, I thought I'd have a look.

Would any of you guys who are experienced with in cylinder pressure analysis have any ideas ref the odd dip and bump on the power stroke/falling pressure area after TDC part of the waveform attached. Ive not really studied In cylinder pressure a whole lot and this "blip" is a new one on me.

Its an F9Q 1.9 D in a Renault, in no start condition and the waveform is taken while cranking.

It has been suggested by a few people who are far more knowledgeable than myself, that it may be piston slack/rock. I was surprised that this would be big enough change in pressure to show in a pressure waveform, however the timing of the event would be correct for the con rod changing angle as the crank passes TDC. So it seems a plausible theory.

Would anyone have any ideas? Do you think the piston movement theory is plausible or not?

BTW, I should just say that I don't think this blip has anything to do with the no start, but I am interested in learning more about in cylinder pressure waveforms, hence the post.

Cheers.
Steve.
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ren.bmp
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Re: In cylinder pressure waveform "blip"

Postby Lion Garage » Mon Oct 31, 2016 11:20 am

Heres the Pico file if anyone wants to look at it.
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HN56DWZ INCYL V INJ A.psdata
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Re: In cylinder pressure waveform "blip"

Postby steevegt » Mon Oct 31, 2016 12:15 pm

It could be a plausible explanation I guess, but it looks like you didn't disable injection.

The pressure "fluctuation" is way to close to the injection event to not notice it.
Try to recapture that with the injectors unplugged. That way we can isolate that variable...

By the way, the injection time doesn't look right also... >15º ATDC?.
This could be the cause of the no starting I guess...
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capture.png
Pressure and Injection event
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Re: In cylinder pressure waveform "blip"

Postby Lion Garage » Mon Oct 31, 2016 2:12 pm

Cheers for the reply.

The injector is not in the cylinder. The only way I could check this was using a dummy injector, the injector is lay across the cylinder head with a current clamp connected. All fuel pipes are blanked at the rail to maintain a fuel pressure signal.

The whole reason I was looking at this was to establish if injection timing looked OK and on the correct cylinder. As stated above, I've not looked at many yet, but the ones I have looked at have a pilot event almost immediately after TDC with a main event following soon after, during cranking. As you say, this example has a pilot event around 7 ATDC and main around 15 ATDC. I'm not really up to speed enough on CR injection timing to know if this is just a quirk of the Renault system or if its plain and simple wrong. But it may well be an issue. I'm waiting on confirmation from someone I think may know the answer, other than that I think the cam may have moved in relation to the cam gear.

I'm working on other cars at the moment and was hoping to get some info for the timing before I get back to it, that will allow me to decide on which direction I take from there.

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Re: In cylinder pressure waveform "blip"

Postby steevegt » Mon Oct 31, 2016 4:19 pm

The injector is not in the cylinder. The only way I could check this was using a dummy injector, the injector is lay across the cylinder head with a current clamp connected. All fuel pipes are blanked at the rail to maintain a fuel pressure signal.


That will isolate the injection event variable. :wink:

Hopping that you find, or someone confirm, what is causing that "blip". Curious with this.

The 15º, I can only say that, at least, it looks odd. Could it be good? Don't know...

Cam and crank signal on top of your capture will be a plus.
The timing could be simply caused by a missing or broken teeth in the crankshaft ring, for instance...
Or crankshaft excessive play, that may correlate to the pressure "blip"...!?
Sorry, just guessing...
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Re: In cylinder pressure waveform "blip"

Postby Lion Garage » Mon Oct 31, 2016 6:41 pm

steevegt wrote:
The injector is not in the cylinder. The only way I could check this was using a dummy injector, the injector is lay across the cylinder head with a current clamp connected. All fuel pipes are blanked at the rail to maintain a fuel pressure signal.


That will isolate the injection event variable. :wink:

Hopping that you find, or someone confirm, what is causing that "blip". Curious with this.

The 15º, I can only say that, at least, it looks odd. Could it be good? Don't know...

Cam and crank signal on top of your capture will be a plus.
The timing could be simply caused by a missing or broken teeth in the crankshaft ring, for instance...
Or crankshaft excessive play, that may correlate to the pressure "blip"...!?
Sorry, just guessing...



Cheers for the input, much appreciated.

Will let you know if I confirm anything on the Blip front. Maybe someone will come along and tell us what's going on.


Ref the no start, Cam/Crank signals both look good and sync within 0.6 of a degree of a known good. Fuel pressure is good, No exhaust or intake restriction, Compressions are OK. As you can see we have injection, it tries to go, but wont quite and smokes. So I'm sure its a timing issue of some sort. I did want to get back to it this PM, but got stuck in another car which I thought was gona be a quick job :(

Cheers.
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Re: In cylinder pressure waveform "blip"

Postby STC » Mon Oct 31, 2016 6:48 pm

Hi Steve

I've been a member for many years but had completely forgotten about the Pico forum,

In that case are you aware of the online waveform library ? (Not the one within the software) The Online version that can only be accessed with the Pico Scope connected to your Laptop / PC.

Here is a link: https://www.picoauto.com/library/waveform-library.

I cannot access it right now (scope not with me) however, I'm sure many of us have had a troublesome F9Q at some time. I'm guessing / hoping that there will be something of use for you in there.

A waveform with Starter Current and an Injection event should be enough to clarify your fuel timing issue.

If you are really stuck then I have access to a similar vehicle, may take a few days, but can be done.
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Re: In cylinder pressure waveform "blip"

Postby STC » Mon Oct 31, 2016 7:17 pm

Hi Again Steve,

Our posts crossed above.

it tries to go, but wont quite and smokes. So I'm sure its a timing issue of some sort.

That goes some way to explain the Rise in Cylinder Pressure ATDC in time with an Injection event. It is partially firing but cylinder pressure & temperature rapidly drop off. The flame is quenched and the remaining unburnt fuel is dumped into the exhaust. A possible explanation for the smoke & "it tries to go but wont" ??

The above statement, in Blue, cannot be the case with Dummy Injector fitted, Good Injector laying across the Head & Fuel pipes blanked. Varied test conditions will give conflicting results.

Would it be a big deal to put it all back together, exhaust every Non Intrusive testing opportunity available to you. then, hopefully, when you do need to remove a component it will be with good reason
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Re: In cylinder pressure waveform "blip"

Postby Lion Garage » Mon Oct 31, 2016 10:40 pm

STC wrote:Hi Steve

I've been a member for many years but had completely forgotten about the Pico forum,

In that case are you aware of the online waveform library ? (Not the one within the software) The Online version that can only be accessed with the Pico Scope connected to your Laptop / PC.

Here is a link: https://www.picoauto.com/library/waveform-library.

I cannot access it right now (scope not with me) however, I'm sure many of us have had a troublesome F9Q at some time. I'm guessing / hoping that there will be something of use for you in there.

A waveform with Starter Current and an Injection event should be enough to clarify your fuel timing issue.

If you are really stuck then I have access to a similar vehicle, may take a few days, but can be done.


Yep. Im aware of the waveform library. To be honest, I'd not looked there as I hadnt really had cause toneed to look yet. The whole reason for starting this thread was to see if someone had any ideas about the "blip", and I said in the first post I didnt think it was anything to do with the no start, just something I'd noticed and was interested in. The coversation going off on a tangent towards the actual no start issue wasnt my intention, but im happy for it to go that way and always happy to hear the opinions of others and receive help.

I used the WPS as I wanted to check it was injecting in the correct cylinder, I'd already seen the injection event was roughly at peak current on a compression test, however, I find its quite easy to be a couple of degrees out on a compression wave form depending on how you set your rulers. Maybe I need to take a bit more care, will give it a look.

Cheers.
Steve.
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Re: In cylinder pressure waveform "blip"

Postby Lion Garage » Mon Oct 31, 2016 10:54 pm

STC wrote:Hi Again Steve,

Would it be a big deal to put it all back together, exhaust every Non Intrusive testing opportunity available to you. then, hopefully, when you do need to remove a component it will be with good reason


Wouldn't be a big deal as injectors back in already. I was happy I'd done all the non intrusive tests I needed too before I took the injector out, it was quick and easy to do and seemed the sensible next step before checking the cam gear-cam shaft relationship.

Thanks.
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