Cylinder two misfire, possibility that the electrode on the old spark plug broke and is somewhere in the cylinder?

Tiny
DAVIDH1965
  • MEMBER
  • 2007 CHEVROLET COLORADO
  • 2.9L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 220,000 MILES
I purchased this truck this week. It came out of a mechanic shop. The mechanic said all he knows is that it has a misfire in cylinder #2. He changed the spark plugs. I checked the plug which has a very faint smell of gas. I checked the coil pack. Everything seems to be working as it should. I just don't have a compression tester to see what the compression is. Can you give me some advice on what to do next? I may be able to borrow an air compressor to do a leak down test. But what can cause the misfire? I checked these things. The mechanic also said the electrode on the old spark plug broke and is somewhere in the cylinder. I don't know where to look next. Can you give me some advice on what to do next? Thank you
Wednesday, March 22nd, 2023 AT 11:42 AM

5 Replies

Tiny
DAVIDH1965
  • MEMBER
  • 8 POSTS
The mechanic said the electrode on the old spark plug broke off and is somewhere in the cylinder.
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Wednesday, March 22nd, 2023 AT 12:15 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,310 POSTS
Hi,

If it has miles on it since the spark plug broke, chances are the electrode isn't in the cylinder anymore. However, it would be a good idea to use a bore scope to inspect inside the cylinder for damage or pieces of the electrode.

If by some chance the electrode is still there, you should be able to remove it with a small mechanic magnet through the spark plug hole.

As far as the compression, a leak down will help determine if there is an issue. And yes, if the compression is low in the cylinder, it can cause a misfire. Have you tried getting a compression tester at a parts store? Most will lend one to you at no charge.

When the truck is running, is it a constant cylinder 2 misfire? In other words, do you feel it constantly when it's running, or does it only happen under certain conditions? Let me know.

Also, here is what I feel needs to be done at this point: First, ask your mechanic if he has a borescope. If he does, have him check inside the cylinder for damage to the cylinder walls or evidence of any damage to the valves. If there is anything in there from the old spark plug, see if it can be removed with a magnet or even a vacuum supply via a pump and flexible vacuum hose.

If that can't be done, then the compression needs to be tested.

Here is a link that explains how it's done:

https://www.2carpros.com/articles/how-to-test-engine-compression

Below, I attached the directions specific to this vehicle. The expected compression is provided, and it indicates the lowest cylinder compression should not be less than 70% of the highest. If cylinder 2 is below that, try a wet compression test. Basically, put a small amount (about a tablespoon) of oil in the cylinder and recheck. If the compression increases, chances are the rings or cylinder walls are worn. If there is no change, it is likely a problem with a valve leaking.

Let me know what you find or if you have other questions.

Take care,

joe

See pics below.
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Wednesday, March 22nd, 2023 AT 6:51 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 43,057 POSTS
Is the engine making a strange sound when running like, a knocking noise? Also, you should do a compression test on that cylinder to see if any valve got damaged.

Here is a guide that can help:

https://www.2carpros.com/articles/how-to-test-engine-compression

Also, you can use an endoscope to see if there is still something inside the cylinder. Let us know what happens and please upload pictures or videos of the problem so we can see what's going on.
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Wednesday, March 22nd, 2023 AT 6:55 PM
Tiny
DAVIDH1965
  • MEMBER
  • 8 POSTS
A friend came by who has a compression tester. I tested the compression in two cylinders. #2 had 0 psi compression, #3 cylinder had 147 psi, which is about normal. It doesn't make strange noise while running, it just has a pretty bad misfire in cylinder #2.
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Wednesday, March 22nd, 2023 AT 7:17 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,310 POSTS
Hi,

If it is 0 PSI, either we have a valve stuck open or a hole in the top of the piston. We need a borescope to look down into that cylinder so we can determine the cause.

If you don't have one, and most people don't, see if a local parts store has one, they will lend you. Or see if your mechanic has one. This is the next step other than removing the cylinder head.

Let me know.

Joe
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Wednesday, March 22nd, 2023 AT 8:08 PM

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