Usually when you encounter a misfire. It's either spark or fuel and you test it back. I don't think your issue is spark. Just because how random they are.

You really might check your fuel pressure or injectors. I would likely throw in a bottle of seafoam to clean the injectors.

Also these 3.6's are direct injection motors and suck oil into the intake and can get really dirty valves caked in oil. Which cause them not to open/close correctly. Since they are direct injection they don't have fuel that cleans the valves. A lot of guys will pull the intakes on these and manual clean the valves and you can find posts/ instructions on this online how to do that. I've had to tear my engine down and do this, and then also at the same time clean out the intake of oil and clean my throttle body as it's caked too. The butterflies in the throttle body have a hard time opening/closing and can issues that seem like a miss. Get a can of throttle body cleaner. Take off the throttle body and clean it so the butterflies are clean.

Actually thinking more. I would start at cleaning that throttle body first. Take it off the car, 4 nuts, and one plug in. Clean it and get all the oil out and then reinstall and see what happens. Try that first as it's literally the cost of a can of throttle body cleaner and less than an hr of time. That could be your issues and they usually won't ever throw a code.

I think whatever you have it's small and something needs cleaned, injectors, valves, throttle body butterflies, something like that. Otherwise if it was something more it would throw a code as sensitive as what these cars are anymore.

 

+1 for cleaning TB first. Also check one easy access spark plug for condition and gap.

Then if needed could use seafoam spray for direct injection it's tricky but gets valves. Plus Seafoam liquid in gas.

Just Bought A Direct Injection Vehicle - How Do I Use Sea Foam? [SOLVED] | Sea Foam

I am getting a brand new vehicle with a direct injection fuel system. How soon in miles should I start adding Sea Foam to keep the system clean? What should

seafoamworks.com

It's worth a try.

...

 

Not saying this is your problem but it is something I would suggest checking given the year and miles on your vehicle - especially if you live in a 4 season climate where road salt and chemicals are used to melt ice during the winter months.
Since you mention misfires on all cylinders (higher on 1, 3 and 5 but also occurring on 2, 4 and 6) and you have changed plugs on all 6 cylinders and coil on 1, 3 an 5 and nothing changed you may feel you have ruled out an electrical problem.
On a 2017 Impala 3.6L V6 three of the ignition coils (1, 3 and 5) share a common ground terminal via the wiring harness at the rear of the right cylinder head and the other three ignition coils share a common ground terminal via the wiring harness at the rear of the left cylinder head - cannot say for sure without a wiring diagram but an educated guess would be that a 2016 model year uses the same ground locations for the ignition coils. I would suggest checking to make sure these terminals are securely clamped by the bolt and there is no evidence of corrosion where the terminals and the wires connect.

 

Definitely need to find out what is causing the misfiring for one thing. You said you changed the plugs, what about the sparkplug wires also?

Motor mounts would be another thing to check if it is engine and transmission/drive train related on the shudder.

 

Definitely need to find out what is causing the misfiring for one thing. You said you changed the plugs, what about the sparkplug wires also?

Motor mounts would be another thing to check if it is engine and transmission/drive train related.

No plug wires on his '16. Cop.

 

Are you getting oil blow back into the air filter pipe and down into the filter media itself? Have you pulled the PCV valve out from the top of the firewall side cylinder head cover to see if it’s plugged solid.

My 2012 LTZ has the 3.6VVT and it idled rough, shuddered slightly, and misfired when I got it, hence the reason I got is so cheap.

The PCV was plugged solid and oil was soaking into the air filter and box.

I changed out the PCV, drilled the holes out, there are other threads on this, and cleaned up all the oil before replacing the filter.

This took care of my rough idle and the shuddering I had due to misfires on most cylinders

 

Everyone, thanks for your responses so far!!!

I’m going to check out every recommendation that everyone has sent so far, starting with with some Sea Foam and cleaning. I’ll keep everyone posted here, and again, thank you so much!!!

 

EDIT: Here is a link to a video demonstrating what I mean. You can see the fluctuation, and also visibly see and hear the shudder.

Hi everyone!

I used some Sea Foam spray through the throttle body to no avail for the shudder. I feel like my car drives a bit better, though, so I’m going to hit it with a second can just because.

Haven’t had the time to do any of the other suggestions yet, but I’ve noticed a new symptom and I wanted to share with everybody.

While the shudder is occurring, the miles per hour gauge fluctuates up and down quite rhythmically. RPMs do not change. Even when the shudder occasionally happens in cruise, the miles per hour fluctuates. Please let me know if this is indicative of any problems that might not have been mentioned here already.

Also, very very occasionally in idle, the RPMS will fluctuate enough to feel it in the seat. Again, very very occasional.

Again, thank you guys so much!

 

Is it shuddering more when making turns? If shudder when making turns, if so it could be bearings, less likely the bearings though if it happens when going down the road in fairly straight stretches.

If when turning only, check your wheel bearings and the speed sensors wiring and all also (that go through the front wheel bearings.) I had my 8th Generation front left wheel bearing replaced, 2 times and it would shudder or make noise when making a turn each time after. The ABS, Stabilitrack, and Traction Control lights would sometimes come on also, but very intermittent. They shop finally took it for a drive when it was happening (first few times they could not find anything else) and had their advanced ODBII scanner on and saw that the speed sensor was also a problem. Replaced that along with the 3rd wheel bearing in 6 months and it drove for the first time much better. This is a 9th Generation though also.

Try writing up all the issues and when the various things happen and put that into ChatGPT along with the make, model, year and engine size of your vehicle and see what it responds with for possible cause of the shuddering and misfiring.

 

Is it shuddering more when making turns? If shudder when making turns, if so it could be bearings, less likely the bearings though if it happens when going down the road in fairly straight stretches.

If so, check your wheel bearings and the speed sensors wiring and all also (that go through the front wheel bearings.) Does it shudder when making turns, if so it could be bearings. I had my 8th Generation front left wheel bearing replaced, 2 times and it would shudder or make noise when making a turn each time after. The ABS, Stabilitrack, and Traction Control lights would sometimes come on also, but very intermittent. They shop finally took it for a drive when it was happening (first few times they could not find anything else) and had their advanced ODBII scanner on and saw that the speed sensor was also a problem. Replaced that along with the 3rd wheel bearing in 6 months and it drove for the first time much better. This is a 9th Generation though also.

Try writing up all the issues and when the various things happen and put that into ChatGPT along with the make, model, year and engine size of your vehicle and see what it responds with for possible cause of the shuddering and misfiring.

It is not. Shudders all the time regardless of turning or straight. I am taking your idea of AI, though. I am running everything through Gemini and creating a "detailed report" with all of my info just for things to look and see.

 

do the misfires coincide with what you describe as "shudder"? if so they are all on one common bank.

 

this has started on my impala with no codes. i did notice that cylinder 2 has the most misfires and nothing other than fuel has helped. it comes and goes, weird. The weird thing is i have a Exhaust flange leak, on the front Cat, like a hairline crack. i have been noticing that it is coating the Ho2 sensor with soot, which tells me that the O2 sensor might be prematurely bad now cause of the constant heat on the top portion of the connector,causing erratic readings or 2, the exhaust leak is causing enough DATA damage to adjust my fuel trim on the affected bank, entering the shudder, or misfire.

i've been flooring it when it shudders and pressing on the brake pedal to fool the electronics on the tcc so i can clean the internals and it helped as it now only shudders when it wants to lol. there is a tsb were the plates get clogged in the valve body, maybe the shudder is coming from those plates clogged..
that's all i can think of, ill do a drain and fill on my transmission and keep you posted bud.

 

You’re exhaust leak has a lot to do with the misfires and the engine running lean/rich. Your sucking in cool fresh air through a cracked pipe that is supposed to be sealed up and exhausting dirty and hot air from the engine.

Engines are like a big vacuum, if you have a hole in the hose of a vacuum , they don’t work properly, just like an engine. Except engines have sensors, in your case the O2 sensors by the cracked pipe, and the computer that is trying to compensate for the sensors telling it something is wrong

 

Yeah you definetely need to fix that hairline crack in the exhaust flange first before you do anything else. I didn't know you had that or I would told you that should be your main focus. I had the same thing and it caused a very small miss.

I did not have to take my Cat off. It was only cracked at the top. I just removed the two top bolts and studs for more clearance when I welded it. I took my MIG and ran a bead from one side to the other side on the top. It fixed it completely. There were no more issues and I did not have to buy any new gaskets or a new Cat. It fixed my small miss I had in my engine.

If the crack is all the way around, you can remove that cat completely. It's 4 nuts at the engine and two bolts at the bottom. Then lay it on a table and weld it all the way around. If you can't weld, you would just have to take it to someone to weld it. Either take the cat off or drive it to an exhaust shop and have them weld it.

But knowing that is cracked now, fix that before you do anything else. That could very be your issue. In fact I almost bet money it is. Those exhaust leaks can cause everything you are describing.

 

Do you think that this could be potentially be the issue in my case too? When doing an oil change the other day I saw a decent crack after the cat and after the O2 sensor. I am planning on fixing it soon regardless.

 

My only other suggestion. If you do weld this yourself. From my days at a body shop, you can warp stuff with a welder if you get it too hot. I didn't run a continuous pass on the Cat. I ran like 1/4'' beads and then hit it with a blow chuck to cool it down to the touch before I did my next 1/4'' bead. It might not be necessary as the CAT gets really hot. But I could see my luck of warping that flange or causing damage to something else. I covered the whole engine and fenders with a welding blanket to make sure I didn't get hot sparks on anything. Also just make sure you don't have any fuel leaks in the engine bay, or you will have a very bad day.

 

Honestly Bfearnly is 100% right. That will def cause a miss.

I wouldn't even try anything else or do anything else till I get that cracked flange fixed. I think there is a very good chance that is your whole issue.

 

that has to be it bud. we shall fix and report. i have an appointment in the exhaust shop next week.

 

Also don't let them talk you into a new CAT. They can be welded. Even completely broken off you could still weld them up. A new Cat thru a parts store is expensive. I've seen some for less than a $100 on ebay and amazon, but mixed reviews if they throw a code or not after you change them.

Initially I was going to throw a new one on my car because that is just how I am, but then saw a lot of the cheap ones throw codes after and then saw the price of new ones from the auto parts stores. so, I just welded mine. Which is totally fine to do so.

 

Hi everyone! This is my first post on the forum, hopefully I can find some answers from other people that know my car better than I do!

I got a 2016 Impala LTZ used (around 155k miles) last year. It has the 3.6L V6 Flex Fuel engine and the 6T70 transmission. Since buying it, I've put 20k miles on it myself, and everything has been great! Until this past month or so...

My car has developed this shudder seemingly out of nowhere. It is truly a random shudder, it can happen under any circumstance, but I typically notice it with light acceleration and under load. However, I've experienced it accelerating on the highway too, even in cruise (but really only going up a hill). The shudder ranges in severity too, going from a little 2 second shudder all the way to a shudder that is very noticeable and lasts for 5+ seconds. I take routine care of my vehicle; oil changes on time or early, changed my transmission fluid, wash it all the time... things a responsible car owner should do. Nothing exactly makes the shudder better, either. I assumed it was a torque convertor problem and have used Shudder Fixx several times to really no avail. I've had the transmission fluid changed several times in order to cycle all of the old fluid out PLUS a bottle of Lubegard Platinum and a bottle of Lucas Transmission Fix. A shop quoted me $4,000 for a full transmission rebuild, and instead of doing that, I decided to keep digging to see if it could be something else...

I've started to consistently have an OBDLink MX+ plugged in and monitoring the data and I see that I have misfires on all cylinders, however, there's no CEL. There's not even a stored code. The number of misfires varies, but it's definitely higher on cylinders 1, 3, and 5.

As a response to seeing this misfire data, I changed the spark plugs on all 6 cylinders. Nothing really changed.

In response to that, I changed the ignition coils on 1, 3, and 5 while on a road trip. The 2 1/2 hour drive home showed 64 misfires on cylinder 1, 87 on cylinder 3, and 47 on cylinder 5. Nothing changed yet again.

I know, yell at me for buying parts without a diagnosis, but I am desperate to get this fixed.

I have tried driving with the MAF unplugged for diagnostic purposes and it didn't really make any difference in the way that the car drove, so maybe I should try replacing that too just for the heck of it. However, disconnecting it gave me codes, so I assume that if it were faulty I'd get codes too?
I have also bought a bottle of MAF sensor cleaner and used it on the sensor and the connector. Nothing.

I have also driven around with an O2 sensor disconnected to put the car into the failsafe mode (for diagnostic purposes), and the car drove differently but I was still experiencing the shudder. All in all, nothing.

For the record, all of these diagnostic tests did not really change the misfire data and did not change the way that the shudder feels. Also, I have not experienced any stalling with the vehicle.

I have also been informed that I should check out my cam position sensors. I haven't yet, but it sounds like it could also be the problem.

Any help would be appreciated. It's a real pain trying to figure out what's wrong with your car when you get no codes! Thanks guys!

Suspect torque converter,fairly common problem..but yes check all the usuall suspects before condeming the torque converter