Car jerks sometimes when at a stop

Hi,

It could be a few different things. For example, an engine vacuum leak can cause a rough idle. Also, fuel pressure can cause this as well as the need for a tune-up.

Is the check engine light staying on when the engine is running? If it is, have the computer scanned for diagnostic trouble codes. Here is a video showing how it's done:

https://youtu.be/InIlnsjOVFA

I realize most people don't own a scanner. However, most parts stores will do it for you free of charge. If the light stays on, have this done, and let me know what codes are present.

One other thought, let me know if you notice any odd odors or smoke from the exhaust. Also, if you can, record it when it happens and upload it for me to hear.

Take care,

Joe

I have a p0456 and p0431 and secondary air injection monitor is hard to set.

Sometimes when I step on the gas pedal I get dark white smoke from the catalytic converter side that's bad.

Hi,

The P0456 is a small evap leak. That isn't causing the issue. The P0431 is related to the catalytic converter.

If you look at the attachment below, it indicates what to check for the P0341. It could be an O2 sensor. Here is a link that explains how to test one:

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

Also, if you have a live data scan tool, watch the voltages from the sensors. It will fluctuate when working. Voltages should be between .1v and .9v. If it stays at one reading, replace the sensor.

Do this and let me know what you find.

Joe

See pic below.

I have a scanner with live data and all four o2 sensors oscillate between .1 and .9 volts I get like .34 and .45 and .87.

Why would smoke be a problem? I do get smoke that smells like gas sometimes.

Hi,

A very rich fuel mixture will cause a gray/black smoke. If the vehicle is running that rich, it will damage things and run poorly.

Since you have that issue, I need you to check the fuel pressure to see if it is within spec.

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

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

I attached the manufacturer's fuel pressure specs below.

Let me know what you find.

Joe

See pic below.

I checked the pids for the short term fuel trims and there -3 and +3. so it can't be the catalytic converter that causes the jerking that's clogged causing backpressure.

Hi,

Where exactly do you see the smoke? Is it from the exhaust?

Let me know.

Take care,
Joe

Yes, my car has dual exhaust. I get it from the exhaust side that has the bad cat but I noticed that time I forgot to connect the fuel pressure regulator vacuum hose and the other time the mad sensor but still it came out only that side.

Hi,

I would think it would come from both sides under those conditions. By any chance are you noticing coolant being used? I wonder if there is an issue with a head gasket on that side. Coolant will burn white when it gets into the combustion chamber.

Take a look through this link. See if any of the symptoms and checks mirror your vehicle.

https://www.2carpros.com/articles/head-gasket-blown-test

Let me know.

Joe

There's no coolant loss it's at the same level since I changed it 4 years ago it's at the max.

I'm really not worried about the smoke, I was just worried about the jerking when the car is stopped. I sometimes feel it when I leave a stop. just thought it was related.

Hi,

I read through all of our conversations. I think I may know what is happening. There is a chance you have a fuel injector leaking causing running issues and smoke from one side of the engine.

What to do is check fuel pump pressure and then fuel pressure drop off. Here is a link you may find helpful. It explains how to test fuel pressure.

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

When you turn the engine off, pay attention to how long it takes for the pressure to drop. t really shouldn't drop more than 5psi within the first minute.

Let me know.

Joe