Misfire or bad performance

KAYVA

MEMBER
2018 MAZDA 3
2.5L
4 CYL
2WD
AUTOMATIC
181,000 MILES

Hello Car people,

I had my spark plugs changed 4 months ago and prior to that 6 months ago. I also had three ignition coils changed roughly a year ago. Now the car seems to misfire ever since two weeks into changing the sparks. This happens when I try to accelerate, but not much of a problem when slowly accelerating and driving. The check engine light did flash previously, and after turning the power off and back on again, it was gone. I drive the car gently as to not trigger a negative response. My question is, can this be a misfire problem or something else? Can it be the last coil that was never changed? The last mechanic stated that it is not the coil but the spark plugs, although the spark plugs were changed 6 months prior, they were blackened or brown at the ends.

Best,
Kayvan Taherpour

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Tuesday, March 29th, 2022 AT 4:30 PM

32 Replies

JACOBANDNICKOLAS

MECHANIC
109,867 POSTS

Hi,

If the spark plugs were black, oftentimes that indicates too much fuel to the engine. If the check engine light didn't flash, there is a good chance it wasn't a misfire.

Here is what I recommend: Because this can be several different things, when the light comes on, take it to a parts store, and before turning the engine off, have them scan it.

Is that something you feel comfortable doing? I don't know if you feel the vehicle is safe to drive.

By the way, the parts you have replaced should not need to be replaced this often.

Let me know your thoughts or if you have questions.

Take care,

Joe

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Tuesday, March 29th, 2022 AT 8:36 PM

KAYVA

MEMBER
18 POSTS

Hello Joe,

Thank you for responding. I would be afraid to drive it to the parts store when the check engine is flashing, because it suffers performance issues when it flashes, and not drivable. When I drive gently it doesn’t flash and still drivable, but I often feel this subtle misfire behavior like jerking during a drive. If there is too much fuel to the engine could the ECM be a problem?

Best,
Kayvan Taherpour

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Tuesday, March 29th, 2022 AT 9:06 PM

JACOBANDNICKOLAS

MECHANIC
109,867 POSTS

Hi,

Chances are it has nothing to do with the ECM. It could be fuel pressure-related, ignition-related, engine vacuum leak, and so on.

If the light is flashing, certainly it is misfiring. So, it wouldn't be a good idea to drive simply because it could damage the catalytic converter. However, we need to find out which cylinder or cylinders to focus on, so a scanner would really be helpful.

Is there anyone you know that owns one or if you call the parts store, will they lend one to you?

Let me know.

Joe

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Wednesday, March 30th, 2022 AT 7:15 PM

KAYVA

MEMBER
18 POSTS

Hi Joe,

I have a scanner, but it’s inexpensive one, and does not show any codes (only $709 $708). I will go ahead to a parts store and try that out, maybe they will lend me a shop-oriented scanner. I will let you know and thank you again.

Sincerely,
Kayvan Taherpour

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Wednesday, March 30th, 2022 AT 8:20 PM

JACOBANDNICKOLAS

MECHANIC
109,867 POSTS

Sounds like a plan. Let me know what you find.

Take care,

Joe

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Wednesday, March 30th, 2022 AT 8:33 PM

KAYVA

MEMBER
18 POSTS

Hello Joe,

So, I Went ahead to AutoZone and had a scanner lended. The results show no codes. I told the guy about the problem, and he mentioned it could be the sparks, and I told him the sparks had been changed 3 months ago. He then mentioned the coils, and I explained all coils except one were changed. He mentioned it’s better to change all coils when a coil needs to be changed. Do you think the one coil could be the problem? It’s sitting on the first cylinder. The first cylinder is the one furthest to the left when looking at the engine, right? Let me know. And thank you again.

Best,
Kayvan Taherpour

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Saturday, April 2nd, 2022 AT 6:16 AM

JACOBANDNICKOLAS

MECHANIC
109,867 POSTS

Well, in most cases, only a coil that is bad is replaced simply because of cost. Also, if you have a bad coil, it should show a misfire code.

By chance, are there any odd odors or smoke from the exhaust? Do you hear any rattling from under the vehicle as the RPMs change? I ask because I'm wondering if you have a partially plugged catalytic converter. Also, have you checked the fuel pressure to make sure it is within the manufacturer's specs?

It's odd that there are no codes set if the light was flashing. However, it may have been deleted if you are driving it under conditions to prevent it from happening.

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

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

Let me know.

Joe

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Saturday, April 2nd, 2022 AT 8:31 PM

KAYVA

MEMBER
18 POSTS

Hi Joe,

No smoke or any current odors coming from the exhaust. However, it is interesting that you bring up the rattling, because when my RPMs are high, only when pushing the throttle completely down to accelerate aggressively, do I hear it for a few seconds from underneath my car. I have not checked the fuel pressure, and how do I check for that? So, I checked the link, and I don’t seem to be experiencing the symptoms I read. Thank you.

Best,
Kayvan Taherpour

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Sunday, April 3rd, 2022 AT 5:25 AM

JACOBANDNICKOLAS

MECHANIC
109,867 POSTS

Hi,

Do me a favor. Take a rubber mallet and tap on the exhaust system to see if you can reproduce the rattle you hear. If you do, note where it is coming from and let me know.

As far as the fuel pressure is concerned, here is a link that explains how it is done:

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

You will need a fuel pressure gauge, but most parts stores will lend one to you.

The pics I attached below are the directions specific to this vehicle. I included both the preservice precautions and after-service precautions. The manufacturer's fuel pressure specifications are included in the directions.

Let me know.

Joe

See pics below.

Images (Click to make bigger)

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Sunday, April 3rd, 2022 AT 3:59 PM

KAYVA

MEMBER
18 POSTS

Hello Joe,

I hope all is well. I will get back to you with updates hopefully next week.

Best,
Kayvan Taherpour

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Sunday, April 10th, 2022 AT 9:58 AM

JACOBANDNICKOLAS

MECHANIC
109,867 POSTS

Hi,

Thanks for the update. Take care and I'll watch for your reply.

Joe

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Sunday, April 10th, 2022 AT 7:17 PM

KAYVA

MEMBER
18 POSTS

Hello Joe,

Thank you for your patience. I will soon have a mechanic check the fuel pressure and run other diagnostics including on the catalytic converter. I’m preparing my budget for the task. A question, is it possible for a fuel pressure problem to oscillate between low and high?

Best,
Kayvan Taherpour

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Thursday, April 14th, 2022 AT 5:58 PM

JACOBANDNICKOLAS

MECHANIC
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Hi,

It is possible if there is an issue with the regulator or a partially plugged filter. However, it isn't common. Do you have symptoms that lead you to think that could be happening?

Let me know.

Joe

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Thursday, April 14th, 2022 AT 7:31 PM

KAYVA

MEMBER
18 POSTS

Hi,

Thinking of the blackened spark plugs from the last change. Plus, sometimes the car idles rough, and the performance behavior I have mentioned, I think it may but not certain. Is the partially plugged filter referring to the catalytic converter?

Best,
Kayvan

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Thursday, April 14th, 2022 AT 7:41 PM

JACOBANDNICKOLAS

MECHANIC
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Hi,

I was referring to the fuel filter. The catalytic converter won't create fuel pressure issues. Do you have reason to suspect the converter?

Let me know,

Joe

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Thursday, April 14th, 2022 AT 9:24 PM

KAYVA

MEMBER
18 POSTS

Hi,

No, but I will have it looked at to make sure a partially plugged catalytic converter as you mentioned is not an issue.

Thank you,
Kayvan

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Thursday, April 14th, 2022 AT 11:58 PM

JACOBANDNICKOLAS

MECHANIC
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Hi,

Okay, I just was wondering. Let me know what you find or if there is anything I can do to help.

Take care,

Joe

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Friday, April 15th, 2022 AT 6:48 PM

KAYVA

MEMBER
18 POSTS

Hey Joe,

When I turn my engine on it idles rough for 30 seconds to a minute, not always, sometimes. It’s the longest time I have witnessed with the car. The rough idles are worse than before. Can this be a fuel pressure problem?

Thank you for your support,
Kayvan

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Friday, April 15th, 2022 AT 7:13 PM

JACOBANDNICKOLAS

MECHANIC
109,867 POSTS

Hi,

Absolutely too much or little fuel pressure can cause this. By any chance, do you have a live data scan tool? If you do, can you let me know what the short-term fuel trims are?

Let me know.

Joe

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Friday, April 15th, 2022 AT 8:28 PM

KAYVA

MEMBER
18 POSTS

Hi Joe,

They seem to oscillate between -6 (negative) to 4 (positive). The car is parked when the numbers were read. When I do city driving the extremes are larger. I inserted a video below with car in park.

Thank you,
Kayvan

Video (Click to make bigger)