[Taylor John]

I have a 2014 XTS with 120k miles, 3.6 paired with a 6T70 trans.
I did spark plugs and a transmission fluid flush.
I have what feels like a shudder, in 5th and 6th gear under light acceleration.
I do not have cel or tcm code set.
I’ve narrowed it down to what I think is a TC lockup problem.
The shudder will happen at any speed but only in 5th & 6th gear, it will happen at lower rpm 1000-1500rpm, and under light throttle the car will begin to shudder as if the TC can’t make up its mind on staying locked up or not.
I believe it’s a lockup issue because it’s only in 5th & 6th and the cars resolution, is to raise the rpms to about 2k or higher, so I believe it’s disengaging TC lock up.
I’m looking for any input as to whether it could be the TC or the control body, but once again I don’t have and codes to go off of.

 

[stevem5215]

I had that exact same thing on a 07' CTS with the 2.8 engine. I would have sworn on a stack of bibles that my trans was the problem. For sure it's a shudder from the torque converter. blah blah blah. NOPE was a misfiring cylinder. Finally set a fault code and I bought the coil pack it needed and new plug for that cylinder and wha la' FIXED IT ! I had that going on for years before it set the code.

 

[Taylor John]

I had that exact same thing on a 07' CTS with the 2.8 engine. I would have sworn on a stack of bibles that my trans was the problem. For sure it's a shudder from the torque converter. blah blah blah. NOPE was a misfiring cylinder. Finally set a fault code and I bought the coil pack it needed and new plug for that cylinder and wha la' FIXED IT ! I had that going on for years before it set the code.

That gives me some hope, I would have expected a cel light by now if it was the transmission, I just don’t have the software to monitor a small misfire.
I believe I read, that the car will set a fault code only if it detects severe misfiring.
Now prior to this whole problem, I had a flashing cel which indicates a severe misfire, maybe two weeks later I started to get a slight shudder but no more cel, so I did the spark plugs, and the shudder remains.
Then I did a flush and I still have a shudder.
A bad coil pack was my original concern, the shudder feels like it could be a transmission problem but it’s also feels very similar to a misfire under load, but with no cel and no way to measure live data I’m kind of stuck on wether or not to replace the coil packs.

 

[somewhereiniowa]

My brand new 2014 Chevy Impala did the exact same thing. Never did figure out why. It had less then 30,000 when turned it back in. It was a lease. Good luck on figuring it out.

 

[Jake Turner]

I would look for carbon tracking on the coil boots.

 

[Taylor John]

I would look for carbon tracking on the coil boots.

I’ll be damned… it’s on more then one spark plug… is there any way to fix this issue short term? Cleaning spark plug grease etc ??

 

[Taylor John]

So all 6 spark plugs have carbon tracking, no carbon tracking on the boots, and all 6 plugs were replaced about 100 miles ago… what did I do wrong…

 

[Excalibur]

None on the boot...chances are that there should be. Did you apply di-electric grease to the coil boot on install? You sound knowledgeable, but maybe the below link might help :

Use Dielectric Grease to Prevent Spark Plug Carbon Tracking – TechLink

gm-techlink.com

 

[Taylor John]

The problem is fixed!
I went back to OE iridium acdelco spark plugs
Part acdelco #41-109
The bad acdelco spark plugs I bought were almost a 1/8 shorter than the OE ones.
I used some acetone to clean the boots because there was ever so slight carbon tracking on them.
I also used permatex dielectric grease.
And upon pushing the coil pack in all the way I felt ever so slight contact between the spring and spark plug terminal, where as I never felt contact with the previous new (bad) acdelco spark plugs.
I went for a test drive manually held the car in 5th & 6th up inclines and no shudder what so ever!

Im assuming the none OE spark plugs where faulty or not a true replacement part like the vendor states they are. I assume this because I had OE spark plugs with no carbon tracking and within 100 miles of the new spark plugs (non OE) I had problems and discovered carbon tracking. I’m not sure if the problem was a shorter plug or dielectric grease. But on my original set of OE plugs I never had dielectric grease.

😁

 

[Jake Turner]

Hey! I got that t-shirt, too!

New plugs and coils cured my intermittent miss at idle and during heavy load.
Glad that helped.

 

[Taylor John]

Hey! I got that t-shirt, too! View attachment 606764
New plugs and coils cured my intermittent miss at idle and during heavy load.
Glad that helped.

Interesting thing was I replaced my spark plugs do to a flashing cel, I never had a shudder, I replaced them with non OE acdelco spark plugs, got a shudder, found carbon tracking, went back to iridium OE plugs and some dielectric grease, no shudder.
I can’t imagine all my my coil packs went bad after a spark plug change, and the vendor excepted a return after explaining my problem.

 

[Submariner409]

Like it or not, once a boot is tracked it's tracked forever. That little lightning strike track on both the plug and boot is as conductive as a piece of wire. The dielectric grease and cleaning may buy you some time but the miss will return fairly shortly.

 

[Jake Turner]

Glad the vendor was cooperative. I don't think my coils were bad, I just didn't know the boots were replaceable until the coils got here. They were just too shiny to resist. New boots may be in your future.