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Intermittent loss of power/acceleration

Tiny
TOTALMC
  • MEMBER
  • 2007 TOYOTA YARIS
  • 4 CYL
  • 200,000 MILES
Car drives fine most of the time, but occasionally experiencing loss of power/acceleration. Will suddenly start sputtering and barely do 30 MPH (which is proving to be dangerous in traffic).

Car has new spark plugs and coils seem fine.

Injectors are all firing (verified only by the sound passing through a screwdriver).

Fuel pump has been replaced.

I'm not sure what to check next. Any guidance is greatly appreciated.
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Monday, August 30th, 2021 AT 5:56 PM

9 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Hi,

If it is intermittent, it could be that the catalytic converter is loose internally and moving around causing flow restrictions. By any chance, have you ever noticed a rattling sound from under the hood or under the vehicle?

Take a look through this link and let me know if you feel it mirrors what you experience.

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

Also, let me know if the check engine light is staying on while the engine is running.

Take care,

Joe
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Tuesday, August 31st, 2021 AT 7:43 PM
Tiny
TOTALMC
  • MEMBER
  • 106 POSTS
Oh, and I forgot it's showing a misfire on #1 and #3. No codes for the catalytic converter, or anything else (just the 301 and 303), but I'll rattle the catalytic converter and see.
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Tuesday, August 31st, 2021 AT 8:09 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Let me know what you find. Also, let me know if you feel the misfire at all times.

Take care,

Joe
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Tuesday, August 31st, 2021 AT 9:38 PM
Tiny
TOTALMC
  • MEMBER
  • 106 POSTS
The car seems to run strong most of the time, but then it will just start to sputter out of nowhere (between 30 and 50 MPH), then again disappear and run fine.
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Tuesday, August 31st, 2021 AT 9:43 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Hi,

Based on your description, it makes me question if there is an issue with fuel pressure. When this happens, have you ever noticed smoke from the exhaust or an odd smell? Also, I noted you replaced the fuel pump. Was the regulator and fuel filter replaced? Have you checked the fuel pressure to make sure it is within the manufacturer's specs?

Let me know. Also, since we have two specific cylinders misfiring, it may be time to do a compression test. It has a lot of miles on it, and there could be an issue there.

Here are two links showing how both procedures would be done:

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

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

Let me know if that has already been tested and if you are comfortable doing them

Joe
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Wednesday, September 1st, 2021 AT 7:13 PM
Tiny
TOTALMC
  • MEMBER
  • 106 POSTS
Car seems to run fine most of the time, only occasionally does this problem arise (but definitely enough to be a problem)

Have not checked the fuel pressure (difficult with this model and do not have proper adapters to get it off the rail), fuel pump was replaced with a coffee can size unit that I believe held everything inside by smoke or odd smell from the pipe. I'm assuming you're thinking head gasket, have not noticed either.

I'll try a compression test next time, but I'm always worried the adapter will screw off the hose and then be impossible to remove from the bottom of the hole.

Thanks again.
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Friday, September 3rd, 2021 AT 7:42 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Hi,

A head gasket was in my mind. However, I was wondering if the fuel mixture was rich. That would cause black or gray smoke and an odd smell. Have you ever noticed that?

Joe
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Friday, September 3rd, 2021 AT 9:14 PM
Tiny
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  • 106 POSTS
No smells or smoke and I do use my nose regularly to diagnose how an engine is running (sometimes I think my nose and ears are the best diagnostic tools).
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Friday, September 3rd, 2021 AT 9:54 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Hi,

I agree. Sound and smell tell a lot. If you have a chance, I would check the fuel pressure to confirm it is within spec. Also, if it is, then I would check compression.

Let me know what you find or if you have other questions.

Take care,

Joe
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Friday, September 3rd, 2021 AT 10:16 PM

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