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Code P0304 cylinder misfire

Tiny
GARYMCC
  • MEMBER
  • 2006 BMW 318I
  • 2.0L
  • 4 CYL
  • 53,000 MILES
I have had all spark plugs and coil packs done and the engine light keeps coming on. Anything else it could be? Thanks
Monday, February 24th, 2020 AT 11:44 AM

12 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,644 POSTS
Hi,

If you still have a misfire, it could be a few things. Since it is limited to cylinder 4, that needs to be our focus.

First, I need to know the following. Do you have a live data scanner? Have you checked fuel pressure? Have you checked for engine vacuum leaks? Are there any exhaust leaks?

If the above checks were done and passed, I need to know about the scanner. I will need the short term fuel trims. If fuel trims are good, then we will have to perform a compression test. Low compression can cause a misfire. A partially plugged catalytic converter can also cause a loss of power and misfire.

I have to be honest. This model isn't offered in the US, so my technical information is very limited. However, I'll do my best to help

Here are links for the above tests:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

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

Let me know. Also, let me know if you can feel the misfire when driving.

Take care,
Joe
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Monday, February 24th, 2020 AT 5:25 PM
Tiny
GARYMCC
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Hi, I have a obd2 scanner. I haven't done any tests not that good with cars. When you open the oil cap there is a bit of pressure. Is that something to worry about or is that because I am getting the misfire? Thanks
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Tuesday, February 25th, 2020 AT 1:30 AM
Tiny
GARYMCC
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  • 9 POSTS
You can feel it when you drive. Thanks
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Tuesday, February 25th, 2020 AT 1:31 AM
Tiny
GARYMCC
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  • 9 POSTS
Could it be the fuel injectors or the catalytic converter, oxygen sensor? People just keep saying could be this could be that.
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Tuesday, February 25th, 2020 AT 12:10 PM
Tiny
JACOBANDNICKOLAS
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A small amount of pressure isn't out of the ordinary. Since you have a live data scanner, can you let me know what the fuel trims are?

And yes it could be any of those. If you can get the fuel trims, it will help me. As far as a an injector, yes. Here is a link that shows how to test one:

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

Let me know.

Joe
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Tuesday, February 25th, 2020 AT 6:46 PM
Tiny
GARYMCC
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  • 9 POSTS
Is that what you wanted to see?
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Wednesday, February 26th, 2020 AT 12:13 PM
Tiny
JACOBANDNICKOLAS
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Hi,

Yes, that's what I needed. The STFT of 99 indicates the computer is adding fuel. This happens when there isn't enough fuel to the engine and too much air. Usually, this is the result of a vacuum leak, low fuel pressure, damaged regulator, bad O2 sensor, which yours looks okay, a cracked exhaust manifold, dirty or damaged fuel injector and so on.

With all of that, have you checked fuel pressure? Also, are there any exhaust leaks?

Let me know.

Joe
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Wednesday, February 26th, 2020 AT 5:51 PM
Tiny
GARYMCC
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Okay, thanks for getting back to me. Won't be able to look at it until Saturday now.
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Thursday, February 27th, 2020 AT 4:50 AM
Tiny
GARYMCC
  • MEMBER
  • 9 POSTS
How would you go about finding out what it is out of all them? What would I be best starting with? Thanks for your help.
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Thursday, February 27th, 2020 AT 1:10 PM
Tiny
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I would start by checking for vacuum leaks. They are most common. Then I would check fuel pressure and the regulator. Here are a couple links to get you started:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Start with that and let me know the results. And try to relax a little over the weekend. Like you, it always seems my cars know when it's the weekend. That's when they break. LOL

Take care,
Joe

Joe
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Thursday, February 27th, 2020 AT 5:46 PM
Tiny
GARYMCC
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Hi, I am going to do them test tomorrow. Is it easy to do a compression test and test the fuel injectors? I have bought a compression test kit. Any help would be great. Thanks
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Tuesday, March 3rd, 2020 AT 3:34 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

The link above shows in general how to perform a fuel pressure test As far as the compression test, here is a link showing how in general it too is done:

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

I don't have the specifics on this model, but the links should help. You are welcome to come back anytime if you have questions.

Let me know if I can help. And no, it isn't hard. A bit time consuming.

Take care,
Joe

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Tuesday, March 3rd, 2020 AT 7:14 PM

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