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Erratic misfire and weird air sound upon motor start

Tiny
HYELINE
  • MEMBER
  • 2014 MAZDA 3
  • 2.0L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 60,000 MILES
Car was driving fine and suddenly started shaking and misfiring. It showed cylinder misfires. I’ve replaced all 4 coils and plugs, the high pressure fuel line. Now it occasionally has that code and P0600 communication code in it. I’m wondering if it’s the PCM?
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Wednesday, February 10th, 2021 AT 12:50 PM

11 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,716 POSTS
Hi,

It does sound like an issue with the powertrain control module (PCM). The code indicates an internal malfunction.

Take a look at the two pics below. The first one explains the code and the second provides the diagnostics for this code. If possible, perform the diagnostics and let me know what you find.

_________________________________

2014 Mazda 3 L4-2.0L (SKYACTIV-G)
Engine On-Board Diagnostics
Vehicle ALL Diagnostic Trouble Codes ( DTC ) Testing and Inspection P Code Charts P0600 P0600:00 Engine On-Board Diagnostics
ENGINE ON-BOARD DIAGNOSTICS
2014 - Mazda3 - Engine

DTC P0600:00 [SKYACTIV-G 2.0, SKYACTIV-G 2.5]

pic 1

Diagnostic Procedure

pic 2

I will watch for your reply. If you have other questions, let me know.

Take care and God Bless,

Joe
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Thursday, February 11th, 2021 AT 4:37 PM
Tiny
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  • MEMBER
  • 10 POSTS
We purchased a used PCM and had it programmed. It changed almost nothing. I have reason to believe the rough idle and accelerating is due to the intake VVT Solenoid. Thought?
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Thursday, February 18th, 2021 AT 7:15 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,716 POSTS
Anything is possible. By any chance, are there any new codes that would lead you to believe it is the VVT?

Let me know,

Joe
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Friday, February 19th, 2021 AT 4:58 PM
Tiny
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  • MEMBER
  • 10 POSTS
Update: with new computer, new coils, car drives smooth. Only has rough idle and accelerating. At higher speeds, you can’t even tell there’s a problem. No codes at all!

However when observing live data, the intake VVT spec has a maximum of 50 and when driving the car while observing that data, when hitting the gas, the figure rises to up to 78! That’s what led me to VVT.
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Friday, February 19th, 2021 AT 5:56 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,716 POSTS
When you accelerate, that is normal. It is indicating an advancement of the timing. Is it running properly now?

Joe
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Saturday, February 20th, 2021 AT 6:31 PM
Tiny
HYELINE
  • MEMBER
  • 10 POSTS
I haven’t gotten a new VVT solenoid. No progress today. Are you saying that the timing needs to be done? After driving it about 25-30 minutes, it did start to misfire again and threw off a code for running too lean P0171.
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Saturday, February 20th, 2021 AT 8:12 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,716 POSTS
Hi,

A lean mixture is usually (but not always) caused by an engine vacuum leak or high fuel pressure. Have you checked either of those? I didn't know that code was present. Start by checking fuel pressure and for vacuum leaks.

Here is a link that explains how to test for a vacuum leak:

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

Here is a link for testing fuel pressure:

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

____________________

Here are the manufacturer's specs for pressure:

Fuel pressure .................... 405-485 kPa [4.13-4.94 kgf/cm2, 58.8-70.3 psi]

Measure the fuel hold pressure after 5 min.

Fuel hold pressure .................... 230 kPa [2.35 kgf/cm2, 33.4 psi] or more

__________________

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

Take care,
Joe
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Saturday, February 20th, 2021 AT 10:05 PM
Tiny
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  • MEMBER
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Fuel pressure is 435.11 at idle.
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Friday, February 26th, 2021 AT 5:44 PM
Tiny
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  • MECHANIC
  • 109,716 POSTS
Hi,

Fuel pressure looks good. Have you checked for engine vacuum leaks? Since it runs well other than idle, at this time, I don't feel it has to do with the VVT. I think there is an engine vacuum leak. Also, by any chance is there an exhaust leak before the o2 sensors? For example, is there a leak at the exhaust manifold?

Let me know.

Joe
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Friday, February 26th, 2021 AT 6:57 PM
Tiny
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Hi Joe,

I sprayed carburetor cleaner all over found no reaction. I just used some Heet water remover and fuel injector cleaner in the tank. I feel like it helped but pushing gas hard while driving set off misfire, blinking check engine light, traction and TPMS.
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Friday, February 26th, 2021 AT 7:09 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,716 POSTS
If it is flashing, that indicates a misfire. Have you checked for new codes? Also, do you have a live data scan tool? If so, could you let me know the short-term fuel trims?

Joe
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Friday, February 26th, 2021 AT 7:31 PM

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