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Discussion Starter · #1 ·
2012 CTS automatic with 50k miles. I am experiencing a shudder sometimes under load.
Can’t figure out if it’s torque converter or some kind of shaft defect?
Not really misfires as the ecm maybe shows 1 random misfire history sometimes.
Any ideas? 50k seems low mileage for a real transmission issue.
 

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2010 CTS4 sedan
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Are the revs constant when it shudders? Is it always under acceleration? Hard or gentle acceleration? Have you recently changed where you buy gas? Any change to tires, brakes or suspension recently?

Are you handy with a scan tool and can you access live data to check your fuel rail pressure, etc.?

A shudder could be anything - after I changed a motor and transmission mount, the difference was astounding.
 

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Discussion Starter · #3 ·
During the shudder I can see the rpm needle move up and down a 1/16th.
No engine/maintenance changes.
Sometimes the shudder is more of a bucking.
I assumed misfire at first but I can feel it more under me towards the rear.
Doesn’t matter hard or soft acceleration and it doesn’t do it every time, and it doesn’t happen as gears change (I’ve watched the gear indicator in sport mode to confirm.) it tends to happen while already in a gear.
I have scan tools. I checked tranny temp was 177, which seems normal.
What am I looking for to scan and what are the normal ranges to expect?
 

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2010 CTS4 sedan
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During the shudder I can see the rpm needle move up and down a 1/16th.
No engine/maintenance changes.
Sometimes the shudder is more of a bucking.
I assumed misfire at first but I can feel it more under me towards the rear.
Doesn’t matter hard or soft acceleration and it doesn’t do it every time, and it doesn’t happen as gears change (I’ve watched the gear indicator in sport mode to confirm.) it tends to happen while already in a gear.
I have scan tools. I checked tranny temp was 177, which seems normal.
What am I looking for to scan and what are the normal ranges to expect?
Run some data to look at the fuel trims, the fuel pressure, etc. by rpm and report back. We need to rule out ignition.
 

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NorthernSRX, what do you mean by Fuel Rail Pressure?
The reason I ask is that my 2012 sport wagon has been totally trouble free (except for the front end squeaking on dips and bumps in cold weather, like many here have reported) But yesterday after gassing up when I started it (it always started on the first click) the starter turned over several revolutions until I turned it off and turned off the headlights and tried again. It started on the first click the second time. Only 49,000 miles on it. New battery last year. Anyone else have that problem, or know what it might lead to? My first thought was that it didn't get gas. THANKS

Are the revs constant when it shudders? Is it always under acceleration? Hard or gentle acceleration? Have you recently changed where you buy gas? Any change to tires, brakes or suspension recently?

Are you handy with a scan tool and can you access live data to check your fuel rail pressure, etc.?

A shudder could be anything - after I changed a motor and transmission mount, the difference was astounding.
 

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**2014 CTS4 Sport Wagon-Luxury**
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also check the low hanging fruit...air filter (cabin air filter too), clean the MAF sensor and the throttle body?...have you had the transmission fluid changed (it is part of the severe service but that is such an ambiguous distinction)...how old and strong is your car's battery?...these cars may act weird with a weak battery doing things seemingly unrelated to a low battery...

you didn't say it was but your CTS isn't an AWD CTS4 is it???...

good luck,

Bill
 

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2007 CTS 3.6 RWD Black 2008 CTS 3.6 DI RWD Red
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NorthernSRX, what do you mean by Fuel Rail Pressure?
The reason I ask is that my 2012 sport wagon has been totally trouble free (except for the front end squeaking on dips and bumps in cold weather, like many here have reported) But yesterday after gassing up when I started it (it always started on the first click) the starter turned over several revolutions until I turned it off and turned off the headlights and tried again. It started on the first click the second time. Only 49,000 miles on it. New battery last year. Anyone else have that problem, or know what it might lead to? My first thought was that it didn't get gas. THANKS
If your sport wagon is hard starting after filling up the gas tank, it could be either your vapor canister purge valve or gas cap. That happened to my 2007 CTS, in mine it was the gas cap.
 

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'14 CTS-V LongRoof; '16 ATS-V Sedan,' 04 Trailblazer 4x4; '10 CTS LongRoof gone but never forgotten
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If you need to crank your engine to build fuel pressure try this: just turn on the ignition, but not to "start". This will allow the fuel pump to pump up the rail. After ten seconds or so try to "start" your car. If it cranks right over then you may have a fuel rail leakdown.

Also pay attention to what nonsmiley just said.
 

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Discussion Starter · #9 · (Edited)
Run some data to look at the fuel trims, the fuel pressure, etc. by rpm and report back. We need to rule out ignition.
Ok so here’s what I did today.
Oil change. (Mobil1).
Top engine cleaner through TB.
Made no shudder difference.
Then, New iridium plugs.
Then went for a 15 min test drive. No difference. Exactly same shudder/bucking.

Bucking stops if I take foot off gas and coast, only happens when under load.
Bucking occurred more frequently during last 5 mins, but did occur the entire ride. Ran my cheapo elm scanner. Here’s the 15 min drive:

598776
598777
598778
598779
598780
598781
 

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2011 CTS Coupe Premium
Orlando - We take orphans
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Boy what a lot of squiggly lines. Is that 16 second (short) duration with foot off gas in middle ? Only thing that jumps out at me is misfires on cyl 1-3-5 (same bank), the knock retard, and the jumpy throttle position, were you doing that ?
 

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Discussion Starter · #11 · (Edited)
Boy what a lot of squiggly lines. Is that 16 second (short) duration with foot off gas in middle ? Only thing that jumps out at me is misfires on cyl 1-3-5 (same bank), the knock retard, and the jumpy throttle position, were you doing that ?
I took the highway to go to get a drivethru and back home. Did one or two WOT (no stutter on wot) and maybe 2 red light stops. Rest is highway drive and drive thru. If it stuttered i eased off the gas.
5 min drive there, 5 mins in drive thru, 5 min drive home.
I do have two different knock retard sensor log data. Not sure why there’s 2 sensors in the scanner.
598790
 

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Those 15,000 kPa fuel rail spikes are amazing - never seen anything like that. Now, I have the 3.6 engine so it's profile is likely different but my fuel rail pressure holds steady at 12,000 kPa at steady cruising (say, between 50 and 60 mph) and sits around 4,000 at idle. Plus those LTFT numbers - while in a decent range - are jumpy as heck. The fuel pressure itself (other than the spikes) is good but what really attracts my attention is those MAP readings - the range is right but I would expect a smooth line and definitely not something like that.

OP: have you checked your PCV hose connections? Is everything nice and tight in terms of air supply? New air filter etc etc? (see Silversport's questions above)
 

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OK TinMan I nagged my wife for years until she let the car Stop BONGING before starting it. I think you are right! I think I simply clicked to Start too soon before the Bonging quit THANKS!

Where's LONG?? He usually likes to throw in some inane nonsense :) :) be careful out there!

If you need to crank your engine to build fuel pressure try this: just turn on the ignition, but not to "start". This will allow the fuel pump to pump up the rail. After ten seconds or so try to "start" your car. If it cranks right over then you may have a fuel rail leakdown.

Also pay attention to what nonsmiley just said.
 

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'14 CTS-V LongRoof; '16 ATS-V Sedan,' 04 Trailblazer 4x4; '10 CTS LongRoof gone but never forgotten
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BONGING, lol. I'm surprised she didn't bong you with her frying pan, lol.
 

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Go ahead, blame me. Everybody does 🙄
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OK TinMan I nagged my wife for years until she let the car Stop BONGING before starting it. I think you are right! I think I simply clicked to Start too soon before the Bonging quit THANKS!

Where's LONG?? He usually likes to throw in some inane nonsense :) :) be careful out there!
Seems like you've got it covered in this thread already. :) :)
 

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Discussion Starter · #18 ·
Those 15,000 kPa fuel rail spikes are amazing - never seen anything like that. Now, I have the 3.6 engine so it's profile is likely different but my fuel rail pressure holds steady at 12,000 kPa at steady cruising (say, between 50 and 60 mph) and sits around 4,000 at idle. Plus those LTFT numbers - while in a decent range - are jumpy as heck. The fuel pressure itself (other than the spikes) is good but what really attracts my attention is those MAP readings - the range is right but I would expect a smooth line and definitely not something like that.

OP: have you checked your PCV hose connections? Is everything nice and tight in terms of air supply? New air filter etc etc? (see Silversport's questions above)
I checked the hoses are tight fitting on the connectors - nothing loose or leaking.
there really isn’t a PCV valve, it’s more of just an elbow. But I did remove it and there’s no blockage and it’s really not oily either. (Hose goes from air intake to pcv elbow and is good.)
Air filter was replaced about 7000 miles ago.
 

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SOUNDS LIKE YOU MIGHT NEED AN INTERNAL FUEL TANK - FUEL PUMP- GET IT QUICK OR YOU'LL BE DEAD ON THE ROAD LIKE I WAS ONE TIME IN MY WIFES MERCURY SABLE STATION WAGON

HASTA LUEGO AMIGOS

IM NEVER COMING BACK TO THIS / WITH THE THREE PART LOG-IN NONSENSE.

I checked the hoses are tight fitting on the connectors - nothing loose or leaking.
there really isn’t a PCV valve, it’s more of just an elbow. But I did remove it and there’s no blockage and it’s really not oily either. (Hose goes from air intake to pcv elbow and is good.)
Air filter was replaced about 7000 miles ago.
 

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Whenever I visit the site I am automatically logged in. Dunno what your prob might be. Maybe computer, or number of posts?
 
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