Misfire or bad performance

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

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

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

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

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

Take care,

Joe

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

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

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

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.

Hello Joe,

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

Best,
Kayvan Taherpour

Hi,

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

Joe

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

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

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

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

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

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

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

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

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

Hi,

Okay, this doesn't add up. It indicates a lean condition, but watching the STFT, they appear normal. In a perfect world, you want them at 0%. However, between -10% and +10% is considered normal.

When the scan tool was providing live data, was the engine running rough?

Joe

Hello Joe,

The engine was not running rough. What if it ranges -17 to 12 a few times when I’m driving the car?

Thank you,
Kayvan

Hi,

That would be normal under a load. I need the STFT when it is running rough. That will let me know if the cause is related to a fuel ratio issue.

I realize that may not be easy to do. LOL If possible, try to get it and let me know what you find.

Take care,

Joe

Hello Joe,

I hope all is well. I recently had my check engine light come on, and checked the code it was P0301 Cylinder 1 misfire. As I stated earlier the sparks have been changed recently. I will take it to my mechanic tomorrow or so and have them check the fuel pressure.

Sincerely,
Kayvan T

Hi,

Thank you for the update. I'm sorry to hear you are still dealing with this issue. If you have a chance, let me know what you find out from the shop. I'm interested in knowing.

Take care,

Joe

Hi Joe,

It’s been a long time since our last email, hope everything is fine. I have an update for you, in short, the motor needs to be replaced, it’s wearing out. I inserted a picture of the comments from the mechanic.

Sincerely,
Kayvan T

Hi,

Thank you for the update. By any chance, did he provide the compression readings? Also, the P0301 is likely because oil got into the spark plug tube. If cylinder 3 compression is low, I would have expected a P0303 as well.

If you do have the compression readings, let me know.

It's nice to hear from you. I hope you have a great Christmas and holiday season.

Take care,

Joe

Yes, he told me cylinder 3 is 30 % lower, and the others are a bit off as well. And yes, there is oil getting onto the spark plugs. I hope you have a good holiday as well.

Sincerely,
Kayvan Taherpour

Thanks for the update. I wish you a great holiday and if you have a chance, let me know how things turn out for you.

Take care,

Joe

You as well, and I also do see a P0421 “Warm Up Catalyst Efficiency Below Threshold Bank1”, and a P300 multiple cylinder misfire. I did have a rough cold start today morning. Again, thank you for the time, and hope you enjoy your holiday and new year.

Sincerely,
Kayvan Taherpour

Hi,

The P0421 shouldn't cause the misfire unless the converter is clogged. However, a failing heated oxygen sensor can set the P0421. The PCM detects that the HO2S output fluctuates from lean to rich in a short amount of time at specified times continuously after recovery from fuel cut control. So, this can be an upstream heated oxygen sensor.

At this point, we need a live data scan tool so we can check the oxygen sensors' voltage readings. Here is a link that explains how to do it.

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

The P0300 is not limited to any one cylinder, but instead random cylinders and misfires. Which potentially moves us away from cylinder 3. What was the outside temp this morning when you started the vehicle? Also, is there any way the individual that checked compression can provide the readings?

Considering the symptoms, I suspect (theory) the oxygen sensor may be the cause of all issues. Check it out and let me know what you find.

Take care, Merry Christmas, and I look forward to hearing from you.

Keep Warm. It's -6 here and a ton of wind. UGH!!!

Joe

It was 7 degrees this morning when I started the car, and the cold start was very bad - the car was shaking and struggling that I felt to turn it off, and few dashboard lights were coming on such as the flashing check-engine light. After half a minute or so I tried it again, and that time it started okay. The dashboard lights were clear. However, a few hours later the check engine light came on prompting me to check with scanner.

I will have them take a look at the oxygen sensor.

-6 degrees is very cold, and with wind.

Thank you for the input, it helps. Merry Christmas.

Sincerely,
Kayvan Taherpour