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Codes P0303, P0306, P0305 and P0300, battery drain, cylinder misfire and running lean

Tiny
TREY5ASH
  • MEMBER
  • 2004 BMW 325I
  • 2.5L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 138,000 MILES
Hello, I just bought the car listed above and have had a few problems with it. It’s throwing p0174 and p0171. I just changed sparkplugs and now it’s throwing codes for cylinders 3, 5, and 6 misfire p0303, p0306, p0305 and p0300. While checking for anything that would obviously cause this, I found that after about 45-50 minutes of the engine running all lights on the dash came on except the battery light and after I cut the car off and tried to cut it back on there was no power. I charged the battery, and it did the same thing. It will run and drive fined up to 3,000 RPMs when it starts sputtering until you cut the car off and cut it back on and it returns to normal.
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Tuesday, February 15th, 2022 AT 3:54 PM

13 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,874 POSTS
Hi,

The codes P0171, and P0174 are related to the air/fuel mixture. Either we have too much fuel or not enough. When this happens, have you ever noticed black smoke from the exhaust? If so, it's likely getting too much fuel. If not, then a lean mixture is the likely cause.

Can your scan tool read live data? If it can, check the short-term fuel trims and let me know what they are. That will help me determine which it is, lean or rich.

Also, if there is no black smoke, you may want to consider checking the fuel pressure to confirm the pump is producing proper fuel pressure. If it's too low, it will cause a lean mixture.

Pic 1 below provides the manufacturer's fuel pressure specifications. Pic 2 shows the description of the codes.

Let me know. Also, let me know the fuel trims if you can get them.

Take care,

Joe

See pics below.
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Tuesday, February 15th, 2022 AT 5:56 PM
Tiny
TREY5ASH
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  • 19 POSTS
I don’t have a live data scanner, but when I pulled codes, it says it’s lean also shows signs of it running lean on the old spark plugs.
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Tuesday, February 15th, 2022 AT 6:02 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,874 POSTS
First, check for leaks (engine vacuum leaks). If there are none, check the fuel pressure. I suspect it will be low. If the fuel filter has never been replaced, this is the time to do it.

Let me know what you find.

Joe
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Tuesday, February 15th, 2022 AT 6:52 PM
Tiny
TREY5ASH
  • MEMBER
  • 19 POSTS
Okay, will do that tomorrow and I will update you with what I find.
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Tuesday, February 15th, 2022 AT 7:09 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,874 POSTS
Hi,

Sounds like a plan. The idea that it indicates a lean mixture on both banks leads me to believe it is either an engine vacuum leak or is related to fuel pressure.

Let me know what you find.

Joe
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Wednesday, February 16th, 2022 AT 4:52 PM
Tiny
TREY5ASH
  • MEMBER
  • 19 POSTS
Okay. So, I haven’t found any vacuum leaks yet and all the lines look good, but I’m going to get the battery tested to see if it’s bad because now the starter will turn over 1-2 times before the battery drains.
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Thursday, February 17th, 2022 AT 4:37 AM
Tiny
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  • MECHANIC
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Hi,

That would be a good idea. Let me know what you find with the battery. I will watch for your reply.

Joe
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Thursday, February 17th, 2022 AT 3:04 PM
Tiny
TREY5ASH
  • MEMBER
  • 19 POSTS
Okay. So, the battery was good, and I have not been able to get the car to do it again. I also have not found any vacuum leaks. So, I'm guessing its fuel related.
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Thursday, February 17th, 2022 AT 4:39 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

That is very possible. My concern is that the battery shouldn't fail after cranking a couple of times. If it passed a load test, I'm wondering if there is something else going on. Are you able to perform a fuel pressure test to see if it is within the manufacturer's fuel pressure specifications?

Here is a link showing in general how it's done:

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

If you look at the pics below, they provide directions specific to your vehicle. The last pic has specs.

Let me know.

Joe

See pics below.
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Thursday, February 17th, 2022 AT 7:20 PM
Tiny
TREY5ASH
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Yes, I can but it will probably be Sunday before I can get the tool to do it. Anything else I should check before then?
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Friday, February 18th, 2022 AT 5:29 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,874 POSTS
At this point, there really isn't anything additional. Once you have the chance to check the pressure, let me know the results.

Take care,

Joe
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Friday, February 18th, 2022 AT 4:07 PM
Tiny
TREY5ASH
  • MEMBER
  • 19 POSTS
The fuel pressure stays at 3.4 bar under load and at idle.
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Friday, February 18th, 2022 AT 4:25 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

That is nearly perfect. There must be a vacuum leak allowing unmetered air to get into the engine. Are there any exhaust leaks? Also, can you get your hands on a live data scan tool? If we know the fuel trims, it will help. Also, we can confirm the oxygen sensors (which the PCM uses to determine the air/fuel mixture needed) are working properly.

If there were other codes, I would be pointing you in a different direction. However, the fuel pressure is great and it's still lean. Somewhere, somehow, it's getting too much air and not enough fuel.

Let me know.

Joe
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Friday, February 18th, 2022 AT 6:58 PM

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