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Discussion Starter · #1 ·
My 2014 Cadenza has been having an on and off problem with a Cylinder 4 misfire. Before I got the car they replaced the spark plug/ignition coil for the 4th cylinder, as well as the fuel pump control module.

Occasionally whenever I start my car it has a very rough idle and I can feel the car shaking. After about a minute of driving the CEL comes on flashing and I can feel the car jerking. I pull over park the car, turn it off, and whenever I restart it, it seems to run fine. (The CEL is still on but not flashing. After driving it for a couple days it eventually turns off until this problem arises again). I’ve recently taken it back to the shop that the car dealership used and they replaced the sensor for the fuel pump control module. It has been running fine but this problem happened again today.

Could it be a bad battery that is causing this issue? The reason I ask is because I can feel this problem occurring immediately once I start my car. I’m curious if a bad battery could cause it not to start properly. It’s also worth noting that I’ve noticed this happens more frequently whenever I haven’t driven the car for 3+ days.

Please let me know if you’ve experienced something similar to this or have any thoughts/suggestions. Thanks!
 

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Have you scanned the vehicle for codes?
If yes and cyl.4 misfire is what you're getting, my first step would be a thorough visual inspection of cylinder #4 (the surrounding area). That's a great first start and one that mechanics will often skip, choosing the parts cannon instead. I guess taking this route will depend on your technical knowledge/abilities.
 

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Discussion Starter · #3 ·
Yeah the code is a misfire on the 4th cylinder. I took it to a Kia dealer a while ago, they said that it was a fuel pump control module. I took it back to the shop that initially did the repair and they told me that it’s not the Fuel pump control module, but rather the sensor.

Everywhere I’m taking my car I’m getting different answers and no one really knows. It’s frustrating to say the least.

The CEL came on flashing Tuesday afternoon (after not driving it for 3 days) and then the CEL was completely gone whenever I started it Wednesday afternoon.
 

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That's my point about mechanics/technicians...because thinking about it logically, neither makes sense (sensor or fuel pump module). A fuel pump module would control fuel flow/pressures so if there was an issue, it would seem that it should affect more than a single cylinder. Same with "the sensor" (sidenote: there are hundreds of sensors on a modern vehicle, so it's imperative that to ask more questions/listen to what techs are telling you and take notes/create a bit of a journal. ESPECIALLY when you're facing an odd issue).

What is your technical knowledge? Are you capable of the visual inspection (meaning are you able to identify different components under the hood)
 

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Also- a flashing CEL is a serious issue and you should stop driving immediately (while it's flashing- of course if safely possible). A flasing CEL indicates an active and continuous misfire which could damage the VERY EXPENSIVE catalytic converter(s).
 

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Discussion Starter · #6 ·
That's my point about mechanics/technicians...because thinking about it logically, neither makes sense (sensor or fuel pump module). A fuel pump module would control fuel flow/pressures so if there was an issue, it would seem that it should affect more than a single cylinder. Same with "the sensor" (sidenote: there are hundreds of sensors on a modern vehicle, so it's imperative that to ask more questions/listen to what techs are telling you and take notes/create a bit of a journal. ESPECIALLY when you're facing an odd issue).

What is your technical knowledge? Are you capable of the visual inspection (meaning are you able to identify different components under the hood)
Not very car savvy. The sensor they replaced was the “fuel tank pressure sensor”

I am able to point out the spark plugs. The 4th cylinder is the only one with a new/different spark plug. So i’m assuming that this was a problem before I bought the car and they tried fixing it with the spark plug, ignition coils, fuel pump control module, and now The fuel tank pressure sensor. But the problem still arises.
 

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Discussion Starter · #7 ·
Also- a flashing CEL is a serious issue and you should stop driving immediately (while it's flashing- of course if safely possible). A flasing CEL indicates an active and continuous misfire which could damage the VERY EXPENSIVE catalytic converter(s).
Yeah I pull over immediately whenever it’s flashing. And turn it off. I wait a minute or two and start it again. And the CEL comes on but no longer flashing and eventually turns off. There is also no more jerking or anything else I can really feel whenever I start up the car again.

it really only ever comes on and flashes after I haven’t driven the car for a couple days. Since none of these other “solutions” have worked, I’m curious if a new batter could fix this issue and give the car a better startup when I haven’t driven it for a couple days.
 

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Understood. Everything I 'd suggest would require a bit of experience with working on vehicles so not sure it would help you in this instance:
  • Visual inspection: ignition coil wiring, nearby vacuum lines (if applicable), intake manifold condition around cyl. 4
  • Remove the plug and look inside cylinder (requires a scope camera)
  • A compression test on the cylinder

What really needs to be figured out: is the misfire fuel, air(vaccuum) or ignition related.
 

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Discussion Starter · #9 ·
Understood. Everything I 'd suggest would require a bit of experience with working on vehicles so not sure it would help you in this instance:
  • Visual inspection: ignition coil wiring, nearby vacuum lines (if applicable), intake manifold condition around cyl. 4
  • Remove the plug and look inside cylinder (requires a scope camera)
  • A compression test on the cylinder

What really needs to be figured out: is the misfire fuel, air(vaccuum) or ignition related.
Thank you so much for your advice! I haven’t trusted any of these mechanics and it sucks because my old mechanic closed up shop a month before I got this car. I think I may have found another trustworthy one that my parents use. So I will talk to him and mention the items you listed!
 

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No problem at all! That's what these forums are all about :)....*I wish this one were as active as the Taurus, Envoy and Impala forums I've been part of in the past but, that's another thread for another day lol

Just please be sure to come back and update the masses on anything you find out/the fix when it happens. I sincerely hope it's resolved for you soon and is something minor!
 

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Understood. Everything I 'd suggest would require a bit of experience with working on vehicles so not sure it would help you in this instance:
  • Visual inspection: ignition coil wiring, nearby vacuum lines (if applicable), intake manifold condition around cyl. 4
  • Remove the plug and look inside cylinder (requires a scope camera)
  • A compression test on the cylinder

What really needs to be figured out: is the misfire fuel, air(vaccuum) or ignition related.
is it possible that they put in the wrong spark plug. or gapped it wrong.
 
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