Misfire after engine warms up?

Tiny
JCUDZIL22
  • MEMBER
  • 2007 SUBARU OUTBACK
  • 2.5L
  • 4 CYL
  • 4WD
  • AUTOMATIC
  • 150,000 MILES
Hello, I've had my car for about two years now and about 8 months ago it started running rough at idle. A couple months later it started stalling out, so I put new spark plugs and wires. After that it ran better for a couple weeks and then started with the rough idle again. I had it checked for a vacuum leak, but nothing showed up. Decided to put a coil in it. Ran better for about a week and then the cam sensor failed. After putting in the cam sensor it ran better but as of lately it's been misfiring and idling rough after the engine warms up. Someone told me it might be an EGR valve, but I have no clue.
Saturday, April 8th, 2023 AT 12:58 PM

14 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
Hi,

It could be a few different things causing the issue. For example, it could be fuel related, an ignition system component failing, a partially clogged catalytic converter, and the list goes on.

So, to try and narrow things down, I would recommend having the computer scanned for diagnostic trouble codes. This should help point me in the right direction.

Here is a link showing how it's done:

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

If you are unable to do it, most parts stores will do it free of charge. Make sure to write down all the codes that are stored and let me know what they are.

Also, let me know if the check engine light flashes when driving.

Take care,

Joe
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Saturday, April 8th, 2023 AT 8:08 PM
Tiny
JCUDZIL22
  • MEMBER
  • 8 POSTS
Alright, so I got it scanned and here are the codes it read:
P0310
P0420
P0457
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Monday, April 10th, 2023 AT 2:13 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
Hi,

The P0420 is related to the catalytic converter. P0457 is an EVAP leak that won't cause what you described. P0310 isn't listed for this year/model. This code indicates a misfire on cylinder 10. Could you have transposed the numbers from P0301 which would indicate a cylinder 1 misfire?

In addition, I need you to check a few things. First, when the vehicle starts acting up and there is a misfire, before turning it off, inspect the catalytic converter to make sure it isn't cherry red. Also, pay attention to the exhaust. Are there any odd sounds or odors coming from it?

Let me know about the code I mentioned.

Take care,

Joe
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Monday, April 10th, 2023 AT 8:41 PM
Tiny
JCUDZIL22
  • MEMBER
  • 8 POSTS
Here's a picture of the codes that it read; I got it printed. I just checked the catalytic converter after driving 40 minutes and it wasn't red. My exhaust does make weird noises, it sounds more like a "putt-putt" than a continuous noise and it sounds bogged down under acceleration up a hill.
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Tuesday, April 11th, 2023 AT 3:15 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
Hi,

The P0301 is a cylinder 1 misfire. So, that will cause a power loss and allow raw fuel to enter the exhaust and could damage the converter.

When were the spark plugs last replaced? Do you know if the spark plugs were ever replaced?

Inspect the spark plug wire and the spark plug in the cylinder. Check the wire to make sure there is nothing damaged or shorting on it. Also, when you remove the spark plug, let me know what it looks like. If possible, take a pic of it and upload it so I can see it.

I attached a pic below, so you know which is cylinder 1.

Let me know.

Joe

See pic below.
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Tuesday, April 11th, 2023 AT 7:19 PM
Tiny
JCUDZIL22
  • MEMBER
  • 8 POSTS
I just replaced the spark plugs and wires a couple months ago, along with the coil, cam sensor and tested for a vacuum leak. When I took the old spark plugs out there was carbon build up on the tips of them.
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Wednesday, April 12th, 2023 AT 2:48 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
Hi,

In this case, it would be a good idea to remove the spark plug from cylinder 1 to see what it looks like. We should be able to determine if there is a coolant issue, fuel issue, or what may be causing the misfire.

Also, do you know if the timing belt was replaced around 100K? Also, by chance do you have a live data scan tool? If you do, check the short-term fuel trims with the engine at operating temperature and forward that info to me.

Let me know.

Joe
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Wednesday, April 12th, 2023 AT 7:17 PM
Tiny
JCUDZIL22
  • MEMBER
  • 8 POSTS
Sorry about the delayed response, the problem continued to worsen so I took it to the nearest Subaru dealership. They quickly diagnosed it as worn piston seals, telling me that it would cost around $6,000 dollars. I might as well buy another car. Apparently, there's 12 to 15psi lost on cylinders 1 and 3. I'm just going to drive it as long as possible before it goes. Right now my odometer is at 155k. Thanks for all the advice given on here anyway.
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Sunday, September 3rd, 2023 AT 6:51 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
Hi,

If the engine oil was changed on a regular basis, this engine shouldn't be worn out. The idea that both cylinders are on the same side of the engine leads me to believe it is a head gasket leak. Did they mention that as a possibility?

Let me know.

Joe
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Sunday, September 3rd, 2023 AT 8:51 PM
Tiny
JCUDZIL22
  • MEMBER
  • 8 POSTS
I bought the car at 127,000 miles on it and changed the oil every 5,000 with fully synthetic oil. I'm not sure if the head gasket was ever replaced or if the people who owned the car before me changed out the oil regularly, but the Subaru dealership didn't mention anything about the head gasket. My engine never overheats and is still drivable.
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Monday, September 4th, 2023 AT 4:40 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
Hi,

Not being there makes it a bit difficult for me. However, that is the first thing I would suspect. The two cylinders are side by side. The head gasket may have failed between the two of them lowering compression in each. If it is a head gasket, it would be more like a 1K dollar job, not 6K.

You may want to get their suggestions. Interestingly, they quoted you a price but didn't tell you what they were doing. Is there anything listed on the repair order?

Let me know.

Joe
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Monday, September 4th, 2023 AT 8:36 PM
Tiny
JCUDZIL22
  • MEMBER
  • 8 POSTS
I do not know I asked another mechanic and he said that it's unlikely that it's the head gasket. My engine never overheats or knocks, I never have any smoke coming out of my exhaust, and I check my coolant every other week and it's always at the same level. Either way I'm done sinking money into the car, whether it's $1,000 or $6,000 it's not worth it anymore. :/
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Tuesday, September 5th, 2023 AT 3:02 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
Hi,

I totally understand. We need to decide when it's time. LOL

Regardless, take care of yourself and feel free to come back anytime in the future.

Joe
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Tuesday, September 5th, 2023 AT 6:22 PM
Tiny
JCUDZIL22
  • MEMBER
  • 8 POSTS
Alright thanks, I appreciated all the advice.
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Wednesday, September 6th, 2023 AT 4:41 AM

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