Blown head gasket...Which cylinder?

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.

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

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

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.

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.

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.

Awwww I missed out on all the fun. :lol:

I like the exhaust cranking the best, this puts a lot of feathers in the hat these waveforms.

Textbook Captures Mr.Coleman!

___deleted photo_____

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.

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.

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.

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!

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

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!

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.

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:

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.

Ah crap, you got me. I was thinking of the deeper vacuum pocket at the bottom of an expansion stroke with in-cylinder pressures.