Strange first time in cylinder pressure waveform?

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3 years 4 months ago - 3 years 4 months ago #44207 by Robbocop33
Using a 500psi pressure transducer in-cylinder to try and get a reading on my Verus Classic,first time i've tried it,fuel disabled,just cranking,this is what i get???Looks like i've got Bart Simpson trapped in there!Doh!
I'm using correct 500psi setting in scope.
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Last edit: 3 years 4 months ago by Robbocop33.

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3 years 4 months ago #44208 by Chad
I have never used a Snap On pressure transducer but, I would recommend reducing the range to a 250 psi scale and change the time base to a 1 or 2 second screen. If that doesn't produce a better wave, then I would change the probe input to Test Lead - Volts DC. Set the voltage scale to the output range of the transducer.

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)

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3 years 4 months ago #44209 by Robbocop33
Don't know if you can adjust the psi scale,it's 500 or down to 100,in the presets anyway.I'll see if there is a way to adjust psi scale though,still familiarising myself with the snap-on.
If that fails i'll try your second suggestion,thanks for replying!Lee.

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3 years 4 months ago #44211 by Matt T
First off is this a Snap-on transducer or something else? If it is something else use voltage instead of the transducer presets.

Looks like you've got way too much time on the screen. That could be killing the sampling rate. Knock it down to 1 second and see how that looks.

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3 years 4 months ago #44212 by Chad

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)

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3 years 4 months ago #44213 by Matt T
One other thing. If you're using a compression tester hose have you taken the Schrader out?

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3 years 4 months ago #44214 by Robbocop33
I've tried all different time scales,still get similar pattern.I also tried doing it on a 5v scale and it never picked up a trace.
I'll maybe try a 2v scale tomorrow and see how that goes.
I just made up a transducer and lead as described somewhere on this forum,at least it's working in some way,just not the correct way!;-)
I just couldn't justify the price of a genuine snap-on transducer just now,been buying lots of tools,machines for key cutting/programming.

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3 years 4 months ago #44216 by Chad

Robbocop33 wrote: I just made up a transducer and lead as described somewhere on this forum


That was, likely, a thread started by Noah. I'm sure he'll chime in, when he logs in. :)

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :-)

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3 years 4 months ago #44217 by Matt T

Robbocop33 wrote: I also tried doing it on a 5v scale and it never picked up a trace.


Did you try that with it connected to one of the 'scopes voltage inputs? Probably won't show a voltage trace from the transducer input.

And have you checked for a Schrader yet? That waveform really looks like it could be caused by one.

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3 years 4 months ago #44218 by Robbocop33
The transducer i made up according to the instructions i found on this site,comprises of positive wire,and ground soldered to two pins of a 9 pin connector which is plugged into the'aux' input of the verus,one wire left (signal wire)is soldered to a banana jack which is plugged into the first channel of the scope.
Regarding schrader,that completely slipped my mind,i'll have to check that,oops! ;-)

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3 years 4 months ago - 3 years 4 months ago #44221 by Noah
Must have used Paul's very well put together tutorial :)
www.scannerdanner.com/forum/diagnostic-t...-transducer.html#859

When you get the schrader valve out of there, I'd be curious to see if you can verify the accuracy of the pressure scale.
My particular sensor does not coincide with the pressure scale and on the Verus Edge, if you aren't using that preset, you can't use the 9 pin for power and ground.
For those reasons I abandoned the 9pin in favor of power and ground via USB.

What sensor did you go with? Looks like it provides pretty good resolution compared to some of the ones I tried.

"Ground cannot be checked with a 10mm socket"
Last edit: 3 years 4 months ago by Noah.

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3 years 4 months ago #44226 by Robbocop33
Yes i was kind of surprised with the resolution too,'looks' like it's going to look good once i get things working properly.
I will report back with exact transducer etc i used later today once i've removed schrader and retested later today.
I have actually bought the proper Snap-on adapter lead so you can use two transducers at the same time,so i am probably going to buy a proper snap-on transducer some day,i was just in the frame of mind what the hell,i'll try a cheap version first!! ;-)

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3 years 4 months ago #44229 by Robbocop33
Well,was at it again this morning,no luck.The only coupling i had to mate up with my transducer and the hose coming from my sparkplug hole was an upper part of a clarke's compression gauge i had,which had a pressure release valve on it.
I removed the pressure relief valve,plugged it up and to my knowledge there aren't any restrictions now from plug hole to the Verus.
I'm still getting the same waveform above??I've tried every setting possible!!It's so frustrating.

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3 years 4 months ago #44230 by Matt T
Try blowing thru' the hose in both directions, with the transducer removed, just to confirm there isn't a restriction in it. If that checks out you could test the response of the transducer by itself with shop air and a blowgun.

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3 years 4 months ago - 3 years 4 months ago #44231 by Robbocop33
I think there was be some other valve inside the hose i have screwed into my spark plug hole,but you can't get it out!!You can't get in there and unscrew it. :-(
Here's a pic of what im screwing into the spark plug hole.I'm pretty sure everyone who is going to do their first in-cylinder scope test will just turn round and grab a hose off a standard compression tester they may have and think it will work?
A lot of people probably don't expect this problem.I might just drill it out then blow out the debrus.
Last edit: 3 years 4 months ago by Robbocop33.

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3 years 4 months ago - 3 years 4 months ago #44614 by Robbocop33
Managed to get there in the end,problem was just the extension i screwed into the spark plug hole,i used one from an old manual compression tester,it must have had restrictions in it.
I bought a hollow brass tube that screws into the spark plug hole,then just screwed in my cheap Chinese 500psi transducer to the top of it.
Scope trace is good,just slight noise in the trace,only thing is now you can't really do much with it ,regarding resizing it,blowing it up and diagnosing it!,which really makes me want a picoscope now!! ;-)too busy at the moment buying tools for key cutting/programming which i've also been learning about.
Last edit: 3 years 4 months ago by Robbocop33.

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3 years 4 months ago #44618 by Noah
Nice, glad you got it working!
If you would care to share a picture of the waveform with us, I would like to see it.

You may not need the Pico just yet, you can squeeze a bit more out of the Verus.
Try setting the time base much lower.
It will look like garbage until you pause the capture, then press the zoom button (magnifying glass in the bottom right corner). That will zoom all the way out on the pattern. From there you can zoom in and out until you get one or two repeating events on the screen.
You can then drag your two vertical cursors around.
I've even seen someone turn on a second chanel just to have a horizontal line on the screen as another cursor.

You can also try a/c coupling the waveform. It's going to throw the voltage scale scale off, but without some more testing, you probably won't have an exact pressure to voltage conversion yet any way.

"Ground cannot be checked with a 10mm socket"

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3 years 4 months ago - 3 years 4 months ago #44620 by Robbocop33
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