Blown head gasket...Which cylinder?

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3 years 3 months ago - 3 years 3 months ago #45440 by Chad
Okay, guys and gals. It's time for another round of "Guess Which Cylinder!"

2002 Chrysler PT Cruiser 2.4L Blown Head Gasket
Firing Order 1-3-4-2 Sync on #1

Use these waveforms to take a guess at which Cylinder is at fault. B)

Building on Tyler's game, this time, you will need to use Filters, Zooming, and a Math Channel (RC is Voltage with AC coupling, it will need to be inverted) to "tune" the waveforms in. Here is a Screen shot of an "un-tuned" capture.



You should be able to produce, and post screenshots, of useful waveforms to determine which cylinder(s) is/are at fault.

Relative compression
drive.google.com/open?id=1JXaRRUnMAfl-KOEUIis9J_Ni4TEuvhGj

Radiator Pulses at idle
drive.google.com/open?id=1wtXiEa654PkESrYkSVmVU4HIIzOgb4C4

Radiator pulses and RC
drive.google.com/open?id=1maJ6GKa7e-YgysO33DIW4mlKxE_hTVlF


PicoScope Software
www.picoauto.com/download/software/sr/Pi...tomotive_6.14.25.exe

"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. :-)
Last edit: 3 years 3 months ago by Chad.
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3 years 3 months ago #45446 by Matt T
Applying a heavy low pass filter to the radiator pulses at idle makes it look like cyl #2.

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3 years 3 months ago #45447 by Matt T
On the cranking waveform #2 definitely looks bad. Compression peak isn't terrible on #3 but the bounce back looks as bad as #2. And #2 and #3 both appear to be causing pressure rises in the rad.

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3 years 3 months ago - 3 years 3 months ago #45448 by Chad

Matt T wrote: Applying a heavy low pass filter to the radiator pulses at idle makes it look like cyl #2.


Nice! :) With even MORE filter, you can see another significant event.

Matt T wrote: And #2 and #3 both appear to be causing pressure rises in the rad.


;)


"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. :-)
Last edit: 3 years 3 months ago by Chad.

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3 years 3 months ago - 3 years 3 months ago #45449 by Chad

Matt T wrote: On the cranking waveform #2 definitely looks bad. Compression peak isn't terrible on #3 but the bounce back looks as bad as #2. And #2 and #3 both appear to be causing pressure rises in the rad.


You are, exactly, right. And, I am sure you know, Matt T. But for others, keep in mind that this is a voltage waveform. It is upside-down for RC. On this 4 cylinder engine and Firing Order, It looks similar to the invert. However on a 6, or 8 cylinder engine, it can look quite different.
To flip it, Go to Tools/Math Channels and check Invert B.


"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. :-)
Last edit: 3 years 3 months ago by Chad.

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3 years 3 months ago #45458 by Tyler
Awwww I missed out on all the fun. :( :lol:

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3 years 3 months ago - 3 years 3 months ago #45459 by Paul P.
I like the exhaust cranking the best, this puts a lot of feathers in the hat these waveforms.

Textbook Captures Mr.Coleman!

___deleted photo_____

Never stop Learning.
Last edit: 3 years 3 months ago by Paul P.. Reason: delete incorrect photo

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3 years 3 months ago #45461 by Matt T
Weycraze,

The ignition signal is waste spark taken with an inductive (RPM) pick-up. The firing events are taller than the waste sparks with this type of probe. It's a little difficult to see with this capture because the voltage scale has cropped the top off the firing events.

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3 years 3 months ago - 3 years 3 months ago #45463 by Chad

Tyler wrote: Awwww I missed out on all the fun. :( :lol:

No one has posted a screen shot of the Intake Manifold waveform, yet. There is something to be seen and explained there, as well. B)

Matt T wrote: The ignition signal is waste spark taken with an inductive (RPM) pick-up. The firing events are taller than the waste sparks with this type of probe. It's a little difficult to see with this capture because the voltage scale has cropped the top off the firing events.


Spot on, again, Matt. ;) This was a error, on my part. :dry: The voltage scale was set to 5 volts, when a minimum of 20 volts should have been used. (This error would not be an issue with the eScope.) The scaling was changed for the other captures.

"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. :-)
Last edit: 3 years 3 months ago by Chad.
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3 years 3 months ago - 3 years 3 months ago #45465 by Paul P.
Matt T, is my picture referenced incorrectly?

Edit, Yes Weycraze your picture is referenced incorrectly!!!!

Thanks Chad, nice set-up!!!!

Everyone, please disregard my picture!!!!!

I need to delete it so not to misguide someone

Paul

Oh, Matt T. thank-you very much for pointing that CRUCIAL tid bit of info out to me!

Never stop Learning.
Last edit: 3 years 3 months ago by Paul P.. Reason: Answered my own question

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3 years 3 months ago - 3 years 3 months ago #45475 by Chad

Weycraze wrote: Thanks Chad, nice set-up!!!!

:oops: My apologies, Paul. It wasn't intentional. :blush: I'm going to blame it on the eScope. :dry: I have gotten use to skipping the channel/scaling setup. ;)

For those that missed it, my bad voltage scaling, in the first waveform, can make 360° of Crank Rotation appear to be 720° of crank rotation.

Bad Voltage Scaling:
Cylinder #1 Compression Spark and Exhaust/Waste Spark both spike over the 5 volt scale. The feedback from the other coil appears to be the waste spark event.


Better Voltage Scaling. With a 20 volt scale (could have been even higher), we can see Cylinder #1 spike higher on it's compression stroke than it does on the the Exhaust Stroke/Waste Spark

"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. :-)
Last edit: 3 years 3 months ago by Chad.
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3 years 3 months ago #45486 by Paul P.
You know what, I had a good laugh!!

But, that is really a good thing for learning purposes. That hits home the importance of using meaningful channel syncs to help aid
in identifying cylinder events.

Also, bad on my part for 'looking' a little too quick, and assuming I was correct on the sync. Especially when looking at someone else's work!

Very good learning experience!

Never stop Learning.

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3 years 2 months ago #45548 by Donut

Chad wrote: No one has posted a screen shot of the Intake Manifold waveform, yet. There is something to be seen and explained there, as well. B)


From the looks of it cylinders #2 and #3 have a deeper intake pull than the other two due to a loss of cylinder charge through the blown head gasket. Use that with the RC and radiator pulse waveforms and you've got a pretty solid case there. Definitely a useful tool in proving out a bad gasket, and somehow a step I always seem to forget about when the time comes to use it. :whistle:


"Don't ever say 'easy' until the check clears."

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3 years 2 months ago #45554 by Chad

Donut wrote: From the looks of it cylinders #2 and #3 have a deeper intake pull than the other two due to a loss of cylinder charge through the blown head gasket.



Close. You're on the right track. ;) However, loss of (volume) charge through the head gasket would not affect the intake stroke, as the exhaust stroke occurs in between. I would argue that the reason for the un-even Intake pulls is due to the crank shaft speed. Under LOW compression, the crank shaft speeds up, causing a DEEPER intake pull on the cylinder that is, simultaneously, on it's intake stroke. Likewise, under GOOD compression, the crank shaft slows down, causing a LOWER intake pull on the cylinder that is, simultaneously, on it's intake stroke.


"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 2 months ago #45559 by Donut
Ah crap, you got me. I was thinking of the deeper vacuum pocket at the bottom of an expansion stroke with in-cylinder pressures.

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