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What might cause misfires on cylinders 3 and 4?

Tiny
ADRIAN627
  • MEMBER
  • 2010 SUBARU FORESTER
  • 2.5L
  • 4 CYL
  • 4WD
  • AUTOMATIC
  • 160,000 MILES
Idle goes down and engine almost shuts off when stepping on brakes. Check engine and traction control lights went on for a few seconds. Checked through an OBD and detected misfires on cylinders 3 and 4.
Friday, August 5th, 2022 AT 9:15 PM

17 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,716 POSTS
Hi,

If you notice pressing the brake pedal seems to cause the issue, there could be a vacuum leak being caused by the power brake booster.

If you open the hood, locate the brake master cylinder on the driver's side firewall. Behind it is the brake booster. Check the vacuum hose going to it. Make sure it is attached, not damaged, and isn't leaking.

I attached a pic of the booster below for your reference.

Also, have a helper press the brake pedal while you listen for any hissing sounds or something that could indicate a leak.

Let me know what you find.

Take care,

Joe

See pic below.
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Friday, August 5th, 2022 AT 11:08 PM
Tiny
ADRIAN627
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Hi Joe,

Thank you. I really appreciate your reply. I'll check it tomorrow morning and let you know. Is it also possible that a dirty throttle body may cause cylinder misfires and low idle?
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Friday, August 5th, 2022 AT 11:31 PM
Tiny
ADRIAN627
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Hi Joe,

The power brake booster seems okay. I turned on the engine and after 30 secs or so, the engine sounded like it was going to shut off. I can also hear a mild clicking sound near where the spark plugs are on the driver side.
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Saturday, August 6th, 2022 AT 10:43 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,716 POSTS
The clicking sound is likely from the fuel injectors. That is normal. Do me a favor. Check to see if you can find any vacuum leaks. The idea that when you apply the brakes it happens worse leads me to think the engine vacuum is low and the booster requesting vacuum is too much.

Here is a link that explains how to locate a leak:

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

Let me know.

Joe
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Saturday, August 6th, 2022 AT 1:47 PM
Tiny
ADRIAN627
  • MEMBER
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Hi Joe,

Sorry for the late reply. I was able to find a mechanic to have a look at my car and he said that there's a leak on the left tie rod. He also found a leak on the water pump. As much as he wanted to fix it, he still has 2 cars to fix. I have brought my car twice to a shop but they were not able to fix it, so I was advised to send the car to the dealership.
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Monday, August 8th, 2022 AT 11:14 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,716 POSTS
Hi,

The tie rod doesn't hold any fluid. It is a solid steel component. As far as the water pump is concerned, it is behind the timing belt cover. I'm not sure how he saw it. Also, a water pump leak or anything with a tie rod won't cause cylinders 3 and 4 to misfire. Did he explain the cause of the misfire?

One other thought. If the water pump needs to be replaced, also replace the timing belt and components. There won't be any additional labor charge. (At least there shouldn't)

Let me know.

Joe
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Monday, August 8th, 2022 AT 9:27 PM
Tiny
ADRIAN627
  • MEMBER
  • 10 POSTS
Hi Joe,

He said that the car may need a tune up. The car is in the dealership now and they didn't see any problems with it as there is nothing that shows up on their computer. So, I decided to leave the car with them for a few more days for them to have more time so they can figure out what the problem really is. When my friend mechanic came over to check the car, the engine suddenly shut off when he parked it. So there really is a problem, it is just not showing up this time.

I'll update you once I get an update from the dealership. Thanks again for your time and my apologies for not getting back to you right away.

Regards,
Adrian
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Friday, August 12th, 2022 AT 8:12 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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No problem, please let us know what happens.
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Saturday, August 13th, 2022 AT 12:29 PM
Tiny
ADRIAN627
  • MEMBER
  • 10 POSTS
Hi Joe and Ken,

I got the car back. The dealer tried to re-create the CEL but to no avail. Their computer showed normal readings. Hoses and sparkplugs are okay. They flushed the power steering fluid as there was a noise when turning. So far, haven't noticed any noise since then. Drove the car today in the city without the AC on and felt the engine vibrated a little while on stop and rpm went down but the engine didn't shut off. I was told that low rpms are kind of normal to older cars. I was advised to call them back if it occurs again.

Thanks again for your time and I will keep you posted as well.

Best regards and stay safe,
Adrian
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Thursday, August 18th, 2022 AT 1:48 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi Adrian,

I'm glad to hear it is running a bit better for you, so thank you for the update. As far as the RPMs at idle, they should be steady at around 600 to 1,000.

Listen, we are here if you have questions or if we can help in any way, so don't be a stranger if you need something. Keep us updated. Both of us are interested in knowing what is happening and want the best for you.

Take care of yourself.

Take care,

Joe
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Thursday, August 18th, 2022 AT 7:46 PM
Tiny
ADRIAN627
  • MEMBER
  • 10 POSTS
Hi Joe,

I really do appreciate you taking time to help me and for answering my inquiries. Thank you so much! Will surely keep you and Ken posted.

Take care and God bless.

Best regards,
Adrian
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Thursday, August 18th, 2022 AT 8:26 PM
Tiny
ADRIAN627
  • MEMBER
  • 10 POSTS
Hi Joe,

So, the car almost stalled again. I guess what my friend was referring to before was the power steering pump. He said it had a leak, but the dealer didn't see it. I checked it earlier and saw grease on the small wire attached to the power steering pump. I ran my fingers on it and there was a small amount of clear oil. I then turned the steering wheel to the left and right and heard a whining sound. I attached a video here so that you can hear it and hopefully give me some advice. I again booked an appointment with the dealer to have it checked.

Thank you and best regards,
Adrian
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Friday, August 26th, 2022 AT 6:58 PM
Tiny
JACOBANDNICKOLAS
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Hi,

I heard it in the video. It does sound like the power steering pump. When you check the fluid, does it appear clean and full? Also, is there any evidence of air bubbles in it?

I don't feel that would cause the engine to almost stall. Does the PS work properly?

Let me know.

Joe
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Friday, August 26th, 2022 AT 7:33 PM
Tiny
ADRIAN627
  • MEMBER
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Hi Joe,

Thanks for your reply. I will check the reservoir tomorrow morning to see if there are bubbles in it and let you know. The fluid is at the right level and was recently put after the dealer flushed the old one. The power steering seems to work just fine, it just makes that whining noise when I turn the steering wheel. I am thinking that if the noise worsens, or if there really is a problem with the pump, it might also affect the rack and pinion.

Thank you,
Adrian
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Friday, August 26th, 2022 AT 8:10 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,716 POSTS
Hi,

It's unlikely that it will do anything to the rack. When this pump was purchased, do you remember if it was a new pump or was it a remanufactured one? I ask because that sound is common with a remanufactured one. I have no idea why, but from experience, most of them do it. Also, when I think back, oftentimes that is what a Ford PS pump sounds like after they get miles on them.

Since it only happens when turning, for certain, it's coming from the pump.

Let me know if I can help in any way.

Take care,

Joe
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Friday, August 26th, 2022 AT 9:08 PM
Tiny
ADRIAN627
  • MEMBER
  • 10 POSTS
Hi Joe,

Thanks for your reply. I don't know if the pump was remanufactured or if it was new when I bought the car. What I do know is that it was not replaced or fixed by the dealer before they handed it over to me. They gave me a copy of the job order for the car. They replaced a left tie rod though as well as the head gasket. If it's the pump, would you recommend to have it replaced right away? Or can the dealer check first if it only needs a new O ring?

Thank you and best regards,
Adrian
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Friday, August 26th, 2022 AT 9:30 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,716 POSTS
Hi,

As long as the steering is working properly, it could stay like that for a long time. You could have the dealer listen to it. If it is still under any warranty from them, they may want to replace it for you.

Let me know.

Joe
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Saturday, August 27th, 2022 AT 6:40 PM

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