New To Picoscope

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22 Mar 2021 14:24 #47658 by CAT785C
New To Picoscope was created by CAT785C
Hello Everyone,
Very happy to be part of the SD Forum. As the title states I am brand new to Pico (just arrived in the mail this weekend) and I have captured my first In-cylinder waveform. Working on 2019 Fusion 2.0L GTDI. Towed in with a crank no-start. Another shop did a short block and now it won't start. RC test shows all cylinders are equal. Capture In-cylinder waveform on Cyl#1. Based upon low TDC pressure, very deep exhaust pocket, and almost no intake activity, suspect restriction in intake system. Based on the waveform, am I on the right track with this? I looked through the Pico Library but was unable to locate a similar waveform.
Thank you in advance.

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  • Chad
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23 Mar 2021 10:48 - 23 Mar 2021 10:50 #47675 by Chad
Replied by Chad on topic New To Picoscope

and almost no intake activity, suspect restriction in intake system.

I don't believe your problem is an intake restriction. The slow cranking speed allows plenty of time for air to enter the cylinder, without creating much vacuum. This is normal, and to be expected. Keep in mind that the pressure transducer is in the CYLINDER. If the intake was restricted, there would be a DEEP vacuum in the cylinder, as the piston moves down. It looks like late valve timing, to me. I would capture Cams/Crank, and compare to a known good.



2017 Fusion 2.0 Known Good

"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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23 Mar 2021 12:55 #47678 by Matt T
Replied by Matt T on topic New To Picoscope

Based upon low TDC pressure, very deep exhaust pocket, and almost no intake activity, suspect restriction in intake system.


The length of the exhaust pocket is the clue here. It extends all the way to BDC because the exhaust valve is opening late.

Next up is the small vacuum pocket during the intake stroke. That is the EVC>IVO event which should have happened around TDC. Reason it's pulling a vacuum is the piston is already traveling down. Looks like there's no valve overlap but that might be the VVT.

Finally pressure doesn't start to build until halfway thru' the compression stroke. Over half the charge air is getting pushed back into the intake before your intake valve closes, late. That's why you've got low compression and is also why you have the deep exhaust pocket.

It would be good to 'scope CKP and CMPs to be thorough, but you've already got enough evidence to pull the timing cover.

If your relative compression was taken with a current clamp post up a screenshot of it too, or the psdata file if you saved it. Wondering whether it might show any evidence of low compression.
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24 Mar 2021 14:38 #47701 by Tyler
Replied by Tyler on topic New To Picoscope

The length of the exhaust pocket is the clue here. It extends all the way to BDC because the exhaust valve is opening late.

Next up is the small vacuum pocket during the intake stroke. That is the EVC>IVO event which should have happened around TDC. Reason it's pulling a vacuum is the piston is already traveling down. Looks like there's no valve overlap but that might be the VVT.

Finally pressure doesn't start to build until halfway thru' the compression stroke. Over half the charge air is getting pushed back into the intake before your intake valve closes, late. That's why you've got low compression and is also why you have the deep exhaust pocket.


Agree 100%. This thing is out of time.

We just had a tech at my shop timing belt one of these engines. He's not an idiot, and still got it wrong the first time. :silly: If your customer decides to have you retime it, make sure you have the correct timing tool set on hand.

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