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Discussion Starter #1
here is one! my 07 didnt start for a dead batterie. changed batterie and then the truck only turned over. towed to dealer and said I only have 20psi compression. they dont know suspect timing jumped??? not positive. dropped motor and said timing is fine!!!!???? what is causing the low compression? truck ran fine up untill the batterie ran into -40 temp. now this.

Going to dealer to look tomorrow. wanting to have an Idea to go there with.
Also - no warrenty left - only on the timing chain.

I think I need a beer!!!!
 

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"dropped motor and said timing is fine!!!!" What do you mean dropped motor? You do not drop a motor to check timing.

As requested above, how many cylinders have 20 psi?

G
 

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Discussion Starter #5
just got back from dealer. 20psi in all cyclinders.
pressure test in TDC and leaking air only on the intake valves.
not leaking on exhaust. but all 12 intake valves leak????
Timing chain is in good shape.
bent valves? scoped the pistons and look like no damage???
everyone is stumped.
 

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Econow said:
just got back from dealer. 20psi in all cyclinders.
pressure test in TDC and leaking air only on the intake valves.
not leaking on exhaust. but all 12 intake valves leak????
Timing chain is in good shape.
bent valves? scoped the pistons and look like no damage???
everyone is stumped.
It is easy to understand everybody being stumped. From an automotive engine view point it does not make sense. There is nothing that can cause those symptoms.

Something about this whole story just does not sound right.

George
 

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Discussion Starter #7
Stumped is right. we have found a used engin and going to put it in. When that is done then we are going to tare the motoe appart and see whats up. let you know what we find.....
 

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Obvious post of the day:

Is the compression tester working properly?
 

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NutBucket said:
Obvious post of the day:

Is the compression tester working properly?
Bingo! A very important question to ask before doing anything invasive. Compression tests can be very inaccurate if not done properly. Was it done when the engine was not completely warmed up? That can cause low compression. Did you notice poor gas mileage, or a significant increase in your fuel consumption prior to this happening? Bad compression doesn't just happen overnight, so if your gas mileage has gotten worse I would believe the low compression. Otherwise, I'd take it out and run the engine hard to the redline for a few rips to clean it out and re-test while the engine is hot.
 

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basspaul said:
Did the 07 have variable valve timing? I'd check that before swapping engines....
It does.
 

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Hoping to resurrect this one a few years later. Currently my 2007 Acadia has nearly the same issue. 20-25 psi on all cylinders. Timing marks all line up. I can’t pinpoint that the valves are leaking (haven’t gotten that far yet but why would they be bent if the chain is lined up?). This chain (set of chains and guides) was replaced about 2 years ago and has been running great until it sat over the weekend then didn’t start Monday morning. I don’t really want to throw an engine in unless I have to but it doesn’t make any sense.
 

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Welcome to the forum.
It's a shame the OP never returned to post a follow-up to this thread. 😕
 

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Thanks, hoping that by resurrecting this thread he’ll comment or someone else can jump in and shed some light on it.
To add to the story, the last time it ran was Friday and I moved the vehicle about 10 ft in my driveway and when I turned it off it didn’t sound right, almost like it had a misfire but not enough for me to worry about that. So it went from that to a crank no start sounding like low compression. Open to ideas?!
 

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You had enough time since Friday to do a cold compression test, open the front cover, and inspect the timing marks? Must be a 'speed wrench!' LOL
 

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I didn’t say what Friday... there was a week between when it went dead and when I took it apart. Anyway to update the maybe 2 people that are looking at this thread I plan to put a new set of chains on and see if that makes a difference. I talked to the guys at Cloyes who make aftermarket chains and they said that sometimes visually it can look lined up but with enough stretch it won’t run. Seems like a lot of stretch but that’s my next step.
 

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I didn’t say what Friday... there was a week between when it went dead and when I took it apart. Anyway to update the maybe 2 people that are looking at this thread I plan to put a new set of chains on and see if that makes a difference. I talked to the guys at Cloyes who make aftermarket chains and they said that sometimes visually it can look lined up but with enough stretch it won’t run. Seems like a lot of stretch but that’s my next step.
With all the cylinders at 20 PSI, a slipped timing chain would be my first guess. Good Luck.
 

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With all the cylinders at 20 PSI, a slipped timing chain would be my first guess. Good Luck.
It's also possible the guides are worn out instead of the chain(s). Good thing the kit comes with those to replace, too.
 

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So tonight I put the new chain set on and had higher compression (50-60 psi). I think took it all apart again, fully removed the cams and did a leak down test only to show that there was air coming out of the intake. Bent valves on a chain that stretched enough after being replaced to years ago. I’m disappointed to say the least, and still confused that it was off enough to bend valves even though all the marks were lined up. I haven’t pulled the heads off yet but I’ll update as I go.
 
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