Random misfire

Tiny
JAKESJ408
  • MEMBER
  • 2003 TOYOTA MATRIX
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 152,000 MILES
Replaced the following: UIM, spark plugs and coil on plugs, air filter, PCV valve and hose, cleaned MAF, replaced Cam sensor, swapped TB from same make model etc. Fuel injectors seem to be working fine. I do not know what else to do besides a pressure and leak down test. Any advice would help and be highly appreciated.
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Tuesday, September 7th, 2021 AT 4:26 PM

19 Replies

Tiny
JOE F
  • EXPERT
Hi,

A misfire can be caused by several different things. Usually, however, it is something simple. Have you checked for engine vacuum leaks? Are there any codes stored other than the random misfire (P0300)?

If you haven't checked for leaks, take a look through this link. It explains how to do it.

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

Also, if it is a specific cylinder that is creating the misfire, it could be lower on compression. That can cause a random misfire and rough idle.

Let me know if there are other codes or if it is specifically a P0300.

Also, if there are no vacuum leaks and no other codes, I would suggest checking engine compression and fuel pressure. Here are two links that explain how it's done:

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

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

Let me know as much as you can. For example, is there an odd odor from the exhaust, do you ever notice smoke from the exhaust, is the engine using coolant, and so on.

Take care,

Joe
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Tuesday, September 7th, 2021 AT 8:12 PM
Tiny
JAKESJ408
  • MEMBER
No vacuum leaks sprayer carburetor cleaner no fluctuations at idle. Also it does this only at idle. The other codes are: p300, 301, 302, 303 and 304.
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Tuesday, September 7th, 2021 AT 9:06 PM
Tiny
JAKESJ408
  • MEMBER
That was going to be my next procedure the compression test.
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Tuesday, September 7th, 2021 AT 9:07 PM
Tiny
JOE F
  • EXPERT
Hi,

So every cylinder is misfiring. It could be fuel pressure; however, the compression test is a good idea as well.

If you have a chance, let me know what you find or if you have other questions. I'll try my best to help.

Take care,

Joe
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Tuesday, September 7th, 2021 AT 9:16 PM
Tiny
JAKESJ408
  • MEMBER
As soon as I do the compression test I'll let you know might be a couple days. I'm in between repair my car from a front end collision work and helping my neighbor with her Toyota. If anything else arises I will definitely ask. Thanks
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Tuesday, September 7th, 2021 AT 9:43 PM
Tiny
JAKESJ408
  • MEMBER
So I checked the codes today and I got p0301 and p0171.
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Wednesday, September 8th, 2021 AT 9:36 AM
Tiny
JOE F
  • EXPERT
Hi,

It is centered on cylinder 1 now. The P0171 indicates a rich fuel mixture. Are you certain the fuel pressure isn't high? If I recall, you didn't test fuel pressure yet and a leak down. That is what I recommend at this point.

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

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

I attached the directions specific to this vehicle below. They include the manufacturer's fuel pressure specifications.

Do me a favor. If your scan tool can provide live data, let me know what the fuel trims are at operating temperature.

Let me know.

Joe

See pics below.

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Wednesday, September 8th, 2021 AT 8:04 PM
Tiny
JAKESJ408
  • MEMBER
Okay, will do when they get back home. I do have live data but the vehicles not here. I was thinking o2 sensors. Glad the code changed from random to a specific.
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Wednesday, September 8th, 2021 AT 8:10 PM
Tiny
JOE F
  • EXPERT
Hi,

I agree. Keep in mind, an O2 sensor can be an issue as well. I should be able to tell by the fuel trims what is happening. When checking, watch how the O2 sensor voltages are changing and let me know their range.

Take care,

Joe
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+1
Wednesday, September 8th, 2021 AT 8:46 PM
Tiny
JAKESJ408
  • MEMBER
Will do. And thanks for your expertise and help. I really appreciate it!
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Wednesday, September 8th, 2021 AT 9:07 PM
Tiny
JAKESJ408
  • MEMBER
Here's the freeze frame data from this morning.
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Wednesday, September 8th, 2021 AT 10:42 PM
Tiny
JAKESJ408
  • MEMBER
Here's the live data from today along with the freezeframe again hope this helps. 1st pic is at idle 2nd under load about 10 MPH 3rd at 35 MPH 4th at 40 MPH.
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Thursday, September 9th, 2021 AT 1:33 PM
Tiny
JOE F
  • EXPERT
Every pic shows -100 on the trims. The PCM is trying to eliminate the amount of fuel entering the engine. It's running very rich.

I have a question because I'm not familiar with your scanner. All the O2 voltages are in the 0 range. Normal voltages will be between.1v (lean) and.9v (rich). Do the voltages on the scanner vary or do they stay constant? Was the engine at operating temp?

An O2 sensor's voltage should cycle normally with constant frequency. An O2 sensor stuck at a fixed voltage (0 is what I see) is an indication of an open O2 circuit or lack of O2 sensor ground.

Let me know.

Joe
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Thursday, September 9th, 2021 AT 3:49 PM
Tiny
JAKESJ408
  • MEMBER
They only moved when I accelerated that gas pedal.
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Thursday, September 9th, 2021 AT 5:09 PM
Tiny
JAKESJ408
  • MEMBER
Yes engine was at operating temperature when I took the screen shots of the live data. I'm using "Fixd" as my live data source.
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Thursday, September 9th, 2021 AT 5:10 PM
Tiny
JAKESJ408
  • MEMBER
So I'm taking it than it's the o2 sensors? If so what ones do I replace all or can I get away with just one I know it's best to replace all at the same time but tight budgets.
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Thursday, September 9th, 2021 AT 5:12 PM
Tiny
JOE F
  • EXPERT
Hi,

If there is no variation in voltage at an idle, it sounds like we have bad O2 sensors. It should show some variation in voltage at idle.

Take a look through this link and let me know if you are comfortable performing it.

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

Next, and the reason I asked about the engine temp when tested, is because the last pic above indicates the engine coolant temp at 78.8 F. If the engine is warmed up and that is what it is signaling, the computer is compensating a rich fuel mixture when the engine is much hotter than it thinks. Thus, the rich fuel mixture.

Let me know.

Joe
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Thursday, September 9th, 2021 AT 5:18 PM
Tiny
JAKESJ408
  • MEMBER
That freeze frame is when the car first started and the code was thrown the engine was just warming up.
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Thursday, September 9th, 2021 AT 5:20 PM
Tiny
JOE F
  • EXPERT
Okay, that makes sense. At this point, we need to check the sensors. If they are not changing voltage signals at all, I have a feeling they could be the problem.

Let me know if you are comfortable performing the test.

Take care,

Joe
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Thursday, September 9th, 2021 AT 7:26 PM

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