engine problem and gas?

Hi,

The idea that it hiccups when you press the brake makes me think there is an engine vacuum leak. When you press the brake, the vacuum booster is depleted, and additional vacuum is needed. You shouldn't feel that. If you do, that is where I would start checking.

Take a look at this link. It explains how to test for a leak.

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

Also, I attached a pic below and highlighted the vacuum brake booster and the vacuum supply hose. Check around there for leaks. It is located under the hood behind the brake master cylinder. Also, make sure the vacuum hose is tight at both ends and there is no evidence of dry rot.

Let me know what you find.

Take care,

Joe

See pic below.

what i know is that the car often feels different after filling up gas and expensive gas improves the problem, so I strongly suspect the problem is most likely related to gasoline.
Many people have given me completely different answers so i am skeptical about your response.

Hi,

As far as the fuel you use, the vehicle doesn't require premium fuel. At least, it wasn't designed to. If it is related to the fuel system, it could be a fuel pressure issue. The symptoms seem to lean that way as well. The only thing that makes me to think vacuum issue is what happens when you press the brake.

An engine vacuum leak is what I consider one of the most common causes of a rough idle and slight hesitation. Absolutely, I could be wrong. The idea that it runs better with premium fuel leads me to think it could be vacuum related as well because a leak can cause a lean fuel mixture. Premium fuel would likely help with that.

Other things to consider would be something like the engine coolant temperature sensor. The powertrain control module receives a signal of the coolant temperature. With that information, it determines the correct air/fuel ratio for the engine to run its best. The PCM doesn't know if the signal is correct. It only knows it is getting one, so it may not set a code.

As you mentioned above, a weak fuel pump can be related or even a failing fuel pressure regulator.

The idea that the engine sounds louder is interesting. By any chance could it be an exhaust leak? If there is a leak before the catalytic converter, it can cause the sensor to think the engine is running lean. If that happens, the PCM increases the fuel to the engine. If it isn't needed, these types of symptoms can occur.

I have a question. By chance do you have or have access to a live data scan tool? If you do, would it be possible for you to let me know what the short-term fuel trims are? Also, the oxygen sensors' voltages would be helpful.

Let me know.

Joe

i don't know what short term fuel trim is
This is what i found using bafx.
There are no codes.

After using expensive gas for a couple months, engine transmission has become little smoother and brake (hiccup? pounding? feels like loose screw on rotor?) has reduced
however recently i noticed engine started making little bit of whining noise

i also noticed recently that engine oil has been a little bit overfilled. Could this cause the problem?

My local mechanic told me this is due to a dirty gas tank. would you find this to be credible?

if i continue driving like this, could it damage anything on my car?

Hi,

It shouldn't damage anything unless it gets worse. Then I would have a concern. As far as the fuel, dirty fuel can certainly cause issues.

You indicated the engine oil is a little over full. Was it like that after the last oil change or has it increased? Does the engine smell like fuel? Are there any creamy substances mixed with the oil?

Let me know.

Joe

i think my mechanic overfilled during oil change. It's about one inch above Full line on the dipstick. i don't smell anything nor see any substance.
does this mean it's okay?

should i be worried about whining noise or VVT monitor bank 1?

do you still think vacuum leak is the number 1 suspect?

Could it be VVT issue?

If the dirty gas tank is the problem, does premium gas sort of heal the problem?

Hi,

The idea that a vacuum leak can cause what was described, I certainly feel it should be checked. And no, premium fuel won't fix a dirty fuel tank. If a dirty tank is a suspect, I would replace the fuel filter a few times to see if the problem stops. If it doesn't stop, I would remove and clean the fuel tank.

I don't feel comfortable with the oil indicator showing approximately one inch over full. That can create issues with the engine. Is it possible for you to have him remove the excess?

Let me know.

Joe

I just realized that there is little bit of bubbles on the dipstick right after driving. Do you think this is the source of the problem? The problem comes and goes. I think I drove nearly 10000 miles since the oil change. Do you think the engine suffered damage already? In that case will I win if I sue the mechanic? I took a picture of overfilled dipstick. Will I need more solid proof?

Hi,

The idea that you drove that far on an oil change (10K miles), that is extreme the manufacturer is recommending every 4,000 miles. Am I correct in what I read?

Let me know. Also, see pics below for service table information.

Joe

See pics below.

It's synthetic oil.
On the obd2 I get VVT bank 1 fail
Should I be worried about it?
What does it mean?
I also get a little bit of whining noise come and go.
Is it normal to have bubbles on dipstick?

Hi,

Just remember to keep the oil serviced. I realize it is synthetic. However, keep in mind that engine oil doesn't wear out. It gets dirty. That happens regardless of whether it is a synthetic or conventional oil.

I have two vehicles that require synthetic of my own. I change them at no more than 5K intervals. It's just a thought.

As far as safety goes, it will just progressively get worse and could lead to internal engine damage. If you plan to keep the vehicle, I would have it repaired.

I'm here if you have questions or if I can help in any way, so let me know.

Take care,

Joe