Misfire code

Tiny
CSTIGLET
  • MEMBER
  • 2005 CHEVROLET COBALT
  • 2.2L
  • AUTOMATIC
  • 180,000 MILES
I need help! My car is saying misfire on cylinders two and three. It also pops up saying the catalytic converter is not running properly. I have cleaned the throttle body, cleaned the mass airflow sensor, replaced the fuel filter, replaced the cranking sensor, replaced the coil pack, spark plugs and rubber boots, checked all of the fuses, replaced air filter& cabin filter. It is still throwing the codes and running rough. Any help would be nice!
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Saturday, May 11th, 2019 AT 9:49 PM

12 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Welcome to 2CarPros.

As far as the codes, what one is coming up for the catalytic converter? Is it a P0420? Also, considering the mileage and the two cylinders are next to each other, we may have an issue with a head gasket. You will need to check engine compression to confirm it is within spec. Also, I need you to check for a head gasket issue.

First, here is a link that explains how to check for a bad head gasket:

https://www.2carpros.com/articles/head-gasket-blown-test

Here are links that discuss engine compression, causes for low compression and how to check compression:

https://www.2carpros.com/articles/symptoms-of-low-compression

https://www.2carpros.com/articles/the-reasons-for-low-compression

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

_____________________________

Here are the directions specific to your vehicle for testing compression. In the directions, it says to disconnect the ignition module. I attached a picture of its location.

Engine Compression Test

Perform the following steps to conduct a compression test.
1. Conduct the following steps to check cylinder compression.
1. Engine should be at room temperature.
2. Disconnect wiring from the ignition module.
3. Remove the spark plugs.
4. Throttle body valve should be wide open.
5. Battery should be at or near full charge.
2. For each cylinder, crank engine through 4 compression strokes.
3. The lowest reading cylinder should not be less than 70 percent of the highest.
4. No cylinder reading should be less than 689 kPa (100 psi).

Important: The results of a compression test will fall into the following categories:
Normal. Compression builds up quickly and evenly to specified compression on each cylinder.
Piston Rings. Compression is low on the first stroke, tends to build up on following strokes, but does not reach normal. Compression improves considerably with the addition of oil.
Valves. Compression is low on the first stroke, does not tend to build up on the following strokes, and does not improve much with the addition of oil. Use approximately 3 squirts from a plunger-type oiler.

___________________

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

Take care,
Joe
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Saturday, May 11th, 2019 AT 10:03 PM
Tiny
CSTIGLET
  • MEMBER
I do not remember the code for the catalytic converter but the next time it pops up I will screen shot it. I will try your suggestion and see what happens. Thank you
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Sunday, May 12th, 2019 AT 5:10 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Happy to help. Listen, if the converter has failed and is plugged, you will experience power loss and most likely a misfire. The extra back pressure can cause engine damage, so keep that in mind.

Feel free to let me know if you have other questions or need help with anything. I will watch for your reply on what is found.

Take care,
Joe
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Sunday, May 12th, 2019 AT 8:12 PM
Tiny
CSTIGLET
  • MEMBER
The catalyst converter code is P0240.
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Sunday, May 12th, 2019 AT 8:22 PM
Tiny
CSTIGLET
  • MEMBER
Sorry it is P0420.
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Sunday, May 12th, 2019 AT 8:23 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Welcome back:

That code indicates the catalytic converter is operating below threshold. With that code, 99% of the time, the converter needs replaced. If it is causing issues with back pressure, it may be the source of the problem. However, I would strongly recommend checking for head gasket issues.

If you get the chance to check for head gasket issues, let me know what is found. Also, let me know what compression is found. With that, I will be better able to direct you. However, the converter will most likely need replaced.

I will watch for your reply. Also, let me know if you have other questions.

Take care,
Joe
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Sunday, May 12th, 2019 AT 8:29 PM
Tiny
CSTIGLET
  • MEMBER
How could it be a head gasket issue when it has never been run hot? And what tools do I need to test the compression?
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Sunday, May 12th, 2019 AT 8:31 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Welcome back:

You will need a compression gauge. Most parts stores will lend you one. As far as the gasket, they get old and fail. It doesn't need to be overheated.

Let me know if I can help.

Take care,
Joe
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Sunday, May 12th, 2019 AT 9:23 PM
Tiny
CSTIGLET
  • MEMBER
Hey so I did the compression test. It was the head gasket. I am replacing the thermostat and the thermostat retainer broke. I have looked everywhere for it and it is a discontinued part so can I run the car without it? Where can I find a replacement for it?
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Saturday, May 25th, 2019 AT 7:02 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
That's not good. Have you tried a salvage yard? Also, are there any u-pull it salvage yards near you? There are several near me and I know there are many 2.2L GM engines. I'm sure if there is a place where they allow you to remove the parts from the salvage vehicles, you could find one.

Let me know.

Joe
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Saturday, May 25th, 2019 AT 8:37 PM
Tiny
CSTIGLET
  • MEMBER
I am going to try and look tomorrow. I have been to 7 different places trying to locate the thermostat housing o-ring. Nobody has them!
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Saturday, May 25th, 2019 AT 8:39 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Wow! That was such a popular engine. I just went to a nationally recognized parts store web page and looked up the o-ring. I'm not to use company names here, but the initials of the store are A Z. Take a look at the attached picture. The picture is for a 2005 cobalt 2.2L.
Do any of those look like what was removed?

Let me know.

Joe
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Saturday, May 25th, 2019 AT 9:04 PM

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