Misfiring and lean bank 1?

Tiny
KWHYNOT
  • MEMBER
  • 2010 TOYOTA YARIS
  • 1.5L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 275,000 MILES
The symptoms started after a collision, but I don't think they are related because it wasn't a big hit. Damage was limited to the passenger side with the headlight busted out and the hood pushed back along with the hood mount bracket.

The issues started with the vehicle stalling a couple of times, while driving it at lower speeds. The following error codes popped up.

P0171
P0300
P0302
P0304

Indicating a lean condition and misfires on cylinder two and four

The following has been done:
MAF - ODB live data looks ok. I tested by checking the value at idle and then doubling the revs and the sensor showed double value. I also cleaned it with MAF cleaner

Air filter, plugs and coils have been replaced

O2 sensor appears to be OK based on the live data

Fuel pump hasn't been tested

I swapped the injectors around and then started getting a misfire on cylinder three, which suggested it was the injectors. I tried replacing them and still get P0171 and P0304. Don't read too much into P0302 missing because it has been inconsistent overall, and I may not have driven far enough for that one to pop up

I haven't performed a compression test or a smoke test to check the intake and vacuum hoses

My thought is this is probably not due to anything like the O2 sensor, fuel pump, or a vacuum leak because that should affect all cylinders equally. Maybe I'm wrong on this?

The only thoughts I have is to check the compression and maybe try a different set of injectors since it's possible the ones I tried weren't any good. And a smoke test if that doesn't prove anything.

I look forward to your input.
Saturday, December 14th, 2024 AT 5:43 PM

3 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,323 POSTS
A smoke test would be good to check the intake for leaks so that is where I would start, and if that is okay, I would check the fuel pressure.

Fuel pressure Standard fuel pressure 304 to 343 kPa (3.1 to 3.5 kgf/cm2, 44.1 to 49.7 PSI)

I must say as well the MAF sensor, even though it was cleaned, can still cause this problem. I would check the GPS reading and compare it to a new sensor. You will need to get a fuel pressure gauge from the auto parts store which you can rent for free or cheap to check the fuel pressure.

This guide can help out as well:

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

I don't think it is the oxygen sensors. How does the engine seem to run? Can you upload a short video so I can see? Please let us know what happens.
Was this
answer
helpful?
Yes
No
Sunday, December 15th, 2024 AT 11:07 AM
Tiny
KWHYNOT
  • MEMBER
  • 4 POSTS
It is down in power and runs rough at idle. It has stalled several times, always when slowing to a stop or turn or when accelerating off of a stop. It is inconsistent, only having stalled a handful of times. I also noticed that it idles ok when first started but starts running rough when it comes off fast idle

Shouldn't a MAF, vacuum leak, fuel pressure, or O2 affect all cylinders? Is it more likely the misfire is causing the lean code? I doubt they are unrelated because they both popped up at the same time

I've included videos showing the ODB data and the engine bay. The roughness is subtle, so it didn't come through well. It's also not as rough as usual. When it's bad the RPMs can fluctuate from as low as 500 up to 1,200.
Was this
answer
helpful?
Yes
No
Sunday, December 15th, 2024 AT 1:12 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,323 POSTS
Thanks for the video, it helps. The engine noise does not sound good, you may have a roller follower that has fallen apart. Also, the MAF sensor readings look low, I would do a compression test and check for vacuum leaks.

This guide can help:

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

and

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

It would be a good idea to remove the valve cover so you can inspect the valvetrain. Please upload more videos of any part you may have found that is questionable.

Was this
answer
helpful?
Yes
No
Tuesday, December 17th, 2024 AT 9:59 AM

Please login or register to post a reply.

Sponsored links