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Discussion Starter · #1 ·
I have a 2015 ST3 and my first year of owning it I had no problems. Then I randomly get a misfire code for on of the cylinders. I reset the codes to see if it would happen again and it didn’t come back for a couple months. Also every time I do get the code it’s not always the same cylinder.

Another question: when I have a cold start (I live in Connecticut) my car idles weird and pops and just isn’t a consistent idle.

Any ideas on what either would be??? I would really appreciate any help I can get.
 

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So remember this is a DI motor, and the injectors expect hundreds of pounds of fuel pressure. The cam driven fuel pump can’t provide that at low RPM.

This means that the LPFP is left to take up the slack until the RPMs get up. This negatively impacts the spray pattern and the fuel atomization in the cylinder.

A better designed piston profile promotes good mixing at low pressure and avoid misfires. This car unfortunately doesn’t have that, and we suffer massively from low RPM misfires.

Those pops you feel are misfires, and the uneven idle is another symptom. Some people get lucky, and have little to no misses, some don’t.

Some things that you can try:
Check plugs -regap
Clean carbon on valves

None of these are guaranteed to work, there’s a good chance they will reduce but not eliminate the misfires. I got 200misfires on my 40 mile commute to work today, almost all of them on warmup before the car went closed loop.


In addition, I’ve found that when it’s really cold I get less misses, when it’s really hot same story, but when it’s around 40-50 high humidity it misses ALOT. This was true even when I was still stock. I also find that I get more misses after a few hard pulls that eventually go away.


Someone with built pistons can chime in, but I’ve heard that aftermarket pistons eliminate this issue.
 

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Discussion Starter · #3 ·
So remember this is a DI motor, and the injectors expect hundreds of pounds of fuel pressure. The cam driven fuel pump can’t provide that at low RPM.

This means that the LPFP is left to take up the slack until the RPMs get up. This negatively impacts the spray pattern and the fuel atomization in the cylinder.

A better designed piston profile promotes good mixing at low pressure and avoid misfires. This car unfortunately doesn’t have that, and we suffer massively from low RPM misfires.

Those pops you feel are misfires, and the uneven idle is another symptom. Some people get lucky, and have little to no misses, some don’t.

Some things that you can try:
Check plugs -regap
Clean carbon on valves

None of these are guaranteed to work, there’s a good chance they will reduce but not eliminate the misfires. I got 200misfires on my 40 mile commute to work today, almost all of them on warmup before the car went closed loop.


In addition, I’ve found that when it’s really cold I get less misses, when it’s really hot same story, but when it’s around 40-50 high humidity it misses ALOT. This was true even when I was still stock. I also find that I get more misses after a few hard pulls that eventually go away.


Someone with built pistons can chime in, but I’ve heard that aftermarket pistons eliminate this issue.

Thank you for putting some light on it but is it going to negatively effect the motor in the long run or is it something that’s just there?
 

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Thank you for putting some light on it but is it going to negatively effect the motor in the long run or is it something that’s just there?
In terms of will it break the motor, no, but it will decrease performance. It’s literally when the ECU fires the spark plug for a cylinder, instead of igniting, it just doesn’t go off.

It’s definitely not good, but I don’t think it will break anything

It’s detected by the crank position sensor actually.


Sent from my iPhone using Tapatalk
 

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Discussion Starter · #5 ·
In terms of will it break the motor, no, but it will decrease performance. It’s literally when the ECU fires the spark plug for a cylinder, instead of igniting, it just doesn’t go off.

It’s definitely not good, but I don’t think it will break anything

It’s detected by the crank position sensor actually.


Sent from my iPhone using Tapatalk
Well that gives me some relief. Thank you for reaching out.
 

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I used to get misfires on startup and idle not hundreds like some people report but I did get a few. I switch to the new ruthenium one step colder plugs Gapped to .026. I never see misfires anymore. Maybe one or two if it's really cold.
 

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I used to get misfires on startup and idle not hundreds like some people report but I did get a few. I switch to the new ruthenium one step colder plugs Gapped to .026. I never see misfires anymore. Maybe one or two if it's really cold.
Got a PN for those? I’d like to give them a try
 

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Discussion Starter · #8 ·
I used to get misfires on startup and idle not hundreds like some people report but I did get a few. I switch to the new ruthenium one step colder plugs Gapped to .026. I never see misfires anymore. Maybe one or two if it's really cold.
Just curious before you switched plugs did you physically get a misfire code? Like the engine light would go on or was it just being about to hear and feel them. I rarely get a check engine light but I often am able to feel and hear the out of rhythm idle
 

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Discussion Starter · #9 ·
I used to get misfires on startup and idle not hundreds like some people report but I did get a few. I switch to the new ruthenium one step colder plugs Gapped to .026. I never see misfires anymore. Maybe one or two if it's really cold.
Just curious before you switched plugs did you physically get a misfire code? Like the engine light would go on or was it just being about to hear and feel them. I rarely get a check engine light but I often am able to feel and hear the out of rhythm idle
 

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Discussion Starter · #10 ·
I used to get misfires on startup and idle not hundreds like some people report but I did get a few. I switch to the new ruthenium one step colder plugs Gapped to .026. I never see misfires anymore. Maybe one or two if it's really cold.
Just curious before you switched plugs did you physically get a misfire code? Like the engine light would go on or was it just being about to hear and feel them. I rarely get a check engine light but I often am able to feel and hear the out of rhythm idle
 

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Just curious before you switched plugs did you physically get a misfire code? Like the engine light would go on or was it just being about to hear and feel them. I rarely get a check engine light but I often am able to feel and hear the out of rhythm idle
I've never thrown a code except for my rear O2 sensor which I had to replace at 20,000 miles. but I could hear and feel the misfires and monitor them on my AP. After switching to the new plugs that are pretty much gone.
 

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Got a PN for those? I’d like to give them a try

Sure do stocky heat range is LTR6BHX / 90495. And one step colder is LTR7bhx. I forget the numbers for the one step colder but you should be able to find it with that. Look up the thread are my spark plugs worn out that has the numbers there.
 

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Sure do stocky heat range is LTR6BHX / 90495. And one step colder is LTR7bhx. I forget the numbers for the one step colder but you should be able to find it with that. Look up the thread are my spark plugs worn out that has the numbers there.
Nice! Thanks! Just ordered a set, Hope they help my situation lol.
 
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