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2010 Acadia 3.6 relative compression

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4 years 3 months ago #36580 by Cheryl
I have my scope set on ac coupling across the battery terminals. I’m trying to convince a shop this thing has major mechanical issues. There not buying it saying they can’t see it having issues. Let me know what you guys think. I didn’t have time to sync a coil or anything just got 1 channel going Here is a pic of the results.
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4 years 3 months ago #36581 by Cheryl
Oh it doesn’t run hardly

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4 years 3 months ago #36584 by Tyler
Did you also invert the voltage trace, in addition to AC coupling? Because if you turn it upside down, you get three strong cylinders and three weak. :silly:

Even if it's inverted, it's still not a good waveform. Timing codes? Glitter in the oil?

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4 years 3 months ago #36587 by Cheryl
I inverted it but didn’t get a pic with my phone. Shop keeps sayin it’s not mechanical. No timing codes

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4 years 3 months ago #36589 by Cheryl
That’s cranking only. I couldn’t find a good cam shaft sensor to crank waveform when I seen those humps missing I was like not good for the guy who owns it sucks to be him. Have you personally done many 3.6 liter timing chain jobs??

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4 years 3 months ago #36591 by Chad
I'm having a hard time wrapping my head around that one. :blink: A sync would be helpful. :) How does it sound while cranking? Does it have the tell-tale rhythmic cadence?

"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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4 years 3 months ago #36592 by Cheryl
Certainly does chad. I didn’t get a chance to take another pic. I didn’t invert it in this pic. Just do what Tyler said. If ya look at it upside down it’s missing 3 cylinder compression. If I hook it up tomorrow I’ll get a sync and inverted pic

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4 years 3 months ago #36593 by Cheryl
I wanted to use my amp clamp but I left it at the house 20 minutes away so I had to do it the ac coupled way hooked up directly across the battery terminals

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4 years 3 months ago #36594 by Chad
Ah, I see it, now. B) I misunderstood. I thought this picture WAS inverted. Makes more sense, now. ;) Low compression on one whole bank.

"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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4 years 3 months ago #36595 by Cheryl
Sorry should of uploaded the good pic. Shop just pissed me off saying it needs an ignition switch nothing mechanical wrong. I said okay let me know how that goes. So chad you do the chains o these engines yet??

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4 years 3 months ago #36596 by Chad
Yes, I have done a few of them. They are not that bad, once you gain access to them.

I flipped your pic:


"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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4 years 3 months ago - 4 years 3 months ago #36598 by Noah
Classic ignition switch :P

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

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4 years 3 months ago - 4 years 3 months ago #36600 by Andy.MacFadyen
None so blind.....

To every one here it shouts cam timing on one bank Only way I can think of to prove it is to demonstrate it is only running on one bank by pull injector or plug wires off on one bank then the other

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)



Last edit: 4 years 3 months ago by Andy.MacFadyen.

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4 years 3 months ago #36609 by Noah
Just for the sake of discussion, how about a blocked converter on one bank?

"Ground cannot be checked with a 10mm socket"

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4 years 3 months ago #36610 by Cheryl
Hmm good thought on the converter. But wouldn’t a clogged converter create higher compression as the engine can’t exhale?? Also I scoped the 4 cam sensors according to Iatn s guy has a known good correlation and mine was way off on one bank
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4 years 3 months ago #36611 by Cheryl
2 of my cam sensors match as they are over laid in the scope shot. But the 2 are no where close. Sorry it’s not labeled the guys from iatn weren’t either. But if they don’t mTch it’s off...
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4 years 3 months ago #36612 by Cheryl
For some reason it wouldn’t let me post my scope capture the same way to make looking at both easier for comparison

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4 years 3 months ago - 4 years 3 months ago #36620 by Tyler
I love doing those chains. B) I'd do a set every day if I could. Maybe two if I got really good!

Let these goons ignition switch it if it makes them feel better. :silly:
Last edit: 4 years 3 months ago by Tyler.

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4 years 3 months ago #36621 by Cheryl
I already did. They called me back to do a 30 minute key relearn on it. Didn’t fix it...

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4 years 3 months ago #36622 by Cheryl
They said tomorrow come back perform a crankshaft variation relearn if I have time to make it back

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