Persistent cylinder 3 misfire?

Tiny
CHIP SAURUS
  • MEMBER
  • 2015 KIA SOUL
  • 1.6L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 115,000 MILES
I've changed the spark plugs and ignition coils on each cylinder. Still had cylinder 3 misfire. Switched all 4 injectors, still had cylinder 3 misfire. Just in case, switched new parts to different cylinders to be sure that cylinder 3 just didn't get a baf part. Still had cylinder 3 misfire. The connections to the coils were extremely brittle and likely didn't have a great connection, so I swapped new connector ends on after removing the brittle ones, still had cylinder 3 misfire. Swapped ignition coils once again, no change. Now I'm thinking possible bad ground wire to the coil or bad wires to cylinder 3 injector. I checked for power at the coils but failed to check for power at the injectors because I didn't think to at the time. What didn't I consider as a misfire cause? There's no power in that cylinder and I don't know what to do next except take it to the shop. I can't afford that at the moment so I'm throwing a Hail Mary to you guys.
Sunday, March 3rd, 2024 AT 11:16 AM

5 Replies

Tiny
BORIS K
  • MECHANIC
  • 762 POSTS
Hello,

A cylinder specific misfire can be caused by:
No or insufficient fuel
No/bad spark
Low compression
Intake air leak

A good read
https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Suggest to first check that there is spark at the suspect cylinder.

How to:
https://www.2carpros.com/articles/how-to-check-for-ignition-spark

How to check if injector is pulsing
https://youtu.be/tA_E6X4ISgQ?si=uLTeq-quSY0ejr3M

How to check for intake air leak:
https://youtu.be/9CPqbaSgcok?si=m6kqqpciod4Gwia4

Next check compression.

https://www.2carpros.com/articles/how-to-test-engine-compression
and
https://www.2carpros.com/articles/symptoms-of-low-compression
and
https://www.2carpros.com/articles/the-reasons-for-low-compression

Cheers, Boris
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Monday, March 4th, 2024 AT 6:11 AM
Tiny
CHIP SAURUS
  • MEMBER
  • 4 POSTS
Thanks for the info. Here's an update. Changed coils, spark plugs and injectors with no change. Compression test revealed zero compression, leak down test resulted in finding out the compression was escaping out the exhaust. The drivetrain warranty company wants to replace the original block with a short block because of the lack of available long blocks. Do you think that will present any problems if that fixes the issue? I'm just worried about dependability issues.
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Wednesday, April 3rd, 2024 AT 10:55 AM
Tiny
BORIS K
  • MECHANIC
  • 762 POSTS
Hello,

Compression leaking into the exhaust would indicate an issue with an exhaust valve either not seating properly or a burnt valve seat. Replacing the short block, bottom part of the engine, would not solve the issue.

Check with them if any loose cylinder heads are available and let the insurance replace the short block plus the cylinder head.

Cheers, Boris
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Thursday, April 4th, 2024 AT 9:15 AM
Tiny
CHIP SAURUS
  • MEMBER
  • 4 POSTS
Thanks, I was thinking that too, but the shop is only doing what the warranty company is allowing them to do based on what the warranty company has experienced. You can't fix stupid, right?
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Thursday, April 4th, 2024 AT 10:23 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,940 POSTS
Nope! The cylinder head is the problem like Boris has indicated.
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Sunday, April 7th, 2024 AT 10:34 AM

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