Code P0304, cylinder 4 misfire?

Tiny
THEHOLDER02
  • MEMBER
  • 2009 CHEVROLET 1500
  • 5.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 180,000 MILES
I need some expert advice. I have a #4-cylinder misfire. We have swapped the coil, spark plug, wire, and fuel injector with the opposite side of the block. The problem does not follow to the other cylinders still showing code P0304. I have had a mechanic do a compression test. It passed with all cylinders are around 120 PSI. They have pulled the valve cover and checked the rocker arm movement. They all checked well. We were told it could be a vacuum leak from the intake manifold. We removed and replaced the gaskets with new ones, but still have a misfire. We did notice after removing the intake the cylinder seemed dry. I really do not know where to go from here, any advice would be appreciated.
Monday, March 20th, 2023 AT 10:50 AM

5 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,137 POSTS
It sounds like it could be a wiring problem or a PCM injector or coil driver has gone out. Let's check to see if there is spark from the coil by following this video:

https://youtu.be/baq_aEWNQ0Y

If you have spark let's, check for injectors pulse which this guide will show you:

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

If you don't have pulse on either let's, check the connection to the PCM. This guide will help, and I have included the wiring diagrams below:

https://www.2carpros.com/articles/how-to-check-wiring

If the wiring is good and you still don't have spark or injector pulse the PCM is bad which you can find a rebuilt unit by searching google or eBay which will come preprogrammed. Check out the images (below). 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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Monday, March 20th, 2023 AT 2:18 PM
Tiny
THEHOLDER02
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Thanks Ken! I will definitely let you and everybody know the progress after I check everything out. Thanks for the quick response.
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Tuesday, March 21st, 2023 AT 1:08 PM
Tiny
KEN L
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No problem, please let us know. :)
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Wednesday, March 22nd, 2023 AT 4:43 PM
Tiny
THEHOLDER02
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Hello Ken,

Sorry it took a while for me to get back to you. We just put a Noid light on the connector going to the fuel injector. We have good flickering; we compared the light to the other good firing cylinders. They seem to have the same brightness and same rhythm. Wouldn’t this mean connection to the injector is good? Is the PCM good because it has a good signal going to connector? Do you think the lack of fuel going to the cylinder could be at the fuel rail? Just at the bottom where it goes into the injector? We didn’t have time to go over the wiring to the PCM yet but if you still recommend, I will get it done.
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Monday, April 3rd, 2023 AT 6:24 PM
Tiny
KEN L
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If the Noid light is flashing it means the connection to the PCM and the PCM is good. The only other thing I can think of is you have a leaky intake valve in one of the cylinders that is affecting #4. I would replace the spark plug one more time, you may have gotten a bad plug and then clear the codes. How does it seem to run?
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Tuesday, April 4th, 2023 AT 10:11 AM

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