Good morning, I have a 2017 Grand Sport. I am driving along and it starts shaking and chugging, like I dropped a cylinder.
Check engine light goes on. Take it to the dealer and he says it is 2 bad sparkplugs.

It happens again and I change all the plugs. It just happened again at 18,000 miles and change #7 plug.

Running fine right now but I would like to know what is causing it.

Thanks

 

Usually if it's spark related it's because the plug wires aren't fully seated on the coil and/or the plug which causes a poor connection. After that, it could be a connector not fully seated on one of the coils. Could be a bad plug wire. Pretty unusual for a plug to go bad unless headers were being installed and someone banged the header into the plug since they didn't remove them. Could be a bad coil that shows its symptoms once it gets hot.

With no data, all the above is just a guess and with no data the sky is the limit with what it could be. May not even be spark related. Could be fuel. Could be lots of things.

What were the code(s)? Since you mention it was "#7 plug" I assume you have a scanner and you're reading the DTC that's turning on the engine light?

 

Agreed, not much to go on here and plugs usually don't just fail.
When did the first two go?
Any mods?
Are they stock palatium plugs?
Were they ever replaced before?
why not just replace them all and be done with it

Dave

 

Had an issue like this this year with my 2017 and previous a friends 2015. The only thing we came up with during the time just before this occurred. We had run the cars for several like 7 to 10 very short run cycles then shut the car off over several days. Not letting the engine get to a some what normal operating temp. Then the miss fires started.

 

from how I'm reading your post, you have replaced 3 of the 8 spark plugs. the third replacement plug may or may not be one of the original two replaced plugs.

the plugs have been in there for over 6 years, the car is barely driven, and it's likely stored in a humid environment -- this is a recipe for disaster. just change them all. there is next to no reason to dick around with replacing them one by one as they begin to have problems.

 

The same thing just happened on my 2017 GS. I was on my way home from a car show and the engine started missing really badly. Pulled over and did a visual check on all hoses and plugs and wires. Because I was a distance from home, I didn't have access to my tools or code reader. Left me no choice but to have it towed to the closest Chevy dealer which wasn't too far away. Then came the waiting game. It sat at the dealership for three weeks before they could look at it. Luckily it wasn't a DD so I could afford to wait. Mechanic was finally able to get to it and said cylinder 7 plug was bad so he replaced all the plugs at a cost of $862. That's over $100 per plug but what could I do? He said it was because I had replaced the plugs with non factory plugs which was the cause of the miss. When I picked up the car, I asked to see the plugs and they were the factory installed Delco iridium plugs, which are supposed to be good for at least 95K miles and the car only had 42K on it. I have a couple of sets of new Delco plugs on the shelf at home, guess I'll just have to start replacing them a lot sooner than 95K miles.

 

What plugs are you using? Is there any chance you got ahold of the fake knock offs that were being sold on Amazon?

 

Nope, in my case, they were the factory installed plugs, never touched them since day one.