Knocking Noise from Engine

It appears that you are reporting two separate issues:
1. Engine pinging
2. Fuel/air mixture is too rich

Regarding engine ping, have you tried using premium fuel to see if that makes a difference?

Regarding the rich mixture, I doubt that all four injectors are bad with only 171K km logged. What does the engine air filter look like (look at the bottom of the filter)?

 

Also, look at the mass air flow sensor located in the air cleaner housing. That sensor has an amber bulb for the ambient air temp sensor. It also has a couple of very fine wires that cannot be seen unless the sensor is removed from the housing. Those wires serve as the mass air flow sensor.

If the amber bulb is grayish looking, that means that it is coated with dirt/dust. Get a spray can of mass air flow sensor cleaner (do not use any other cleaner such as throttle body cleaner.) Remove the sensor from the air cleaner housing and spray it liberally with the cleaner. Do not touch the sensor with anything other than the cleaner spray.

 

If higher octane fuel doesn’t change the noise it really can’t be pinging. It could be just something lose and rattling on the engine or exhaust. Does it make the same noise if (while stationary in drive) you force charge the hybrid battery by pressing brake hard HARD with your left feet and pushing the accelerator with your right feet? You can then adjust the engine rpm with gas pedal trying to get it to produce the noise. If you can do that you can then listen where the noise is coming from.

 

Running to rich for a long time could have resulted in a buildup of carbon deposits in the combustion chamber which will raise your compression ratio and lead to pinging. If the buildup is really bad, even when using higher octane gas the engine can still ping.

See if your mechanic has an micro-camera that can display the inside of the combustion chambers by removing the spark plugs.

 

Pinging and knocking are 2 different things. You need to determine which as they have different courses of action. Pinging sounds like marbles in a can upon load acceleration. Thats detonation.

Knocking is much worse and sounds much lower frequency and much more distinct. Knocking is bad as it reflects lower engine bearing damage. Usually caused by running the car low on engine oil.

Have you ever ran the car so low on engine oil it threw the engine icon on the dash. The yellow icon?

Is there any dash light codes being thrown? Check engine lights? If not then most engine parameters are within specification and that may mean your issue is strictly mechanical.

 

That's good no yellow icon but how are you about checking and maintaining the oil level? Have you ever run the car real low on oil? Keep after it as most hi mileage Prius eat oil.

Strictly mechanical means well its strictly mechanical....not sensored...something bent, broken, loose, worn out, hanging from the bottom of the car etc...something that does not have a sensor monitoring it. Like blown bottom end engine bearings. There's no sensor for that. Sometimes if the bearing damage is significant it will throw a misfire code due to lower end vibration that throws the crank/cam sensors out of whack.
if the car has severe detonation it will engage the knock sensor and that circuit will command the engine to retard timing to mitigate detonation making the engine feel very loaded and sluggish. If the car has lower end bearing damage it may not engage the knock sensor and the engine will still feel peppy but engine failure is imminent. Also bearing damage is most notable if you put the engine in inspection mode (go on youtube and search Prius Inspection Mode) and then get under the front of the car and have a good listen for metallic banging or lower end booming.

We are seeing lots of posts about G2 engine damage due to poorly maintained oil. The 1.5 motor is extremely tough but will not tolerate 0 oil pressure.

Detonation has a unique sound to it. Like marbles in a can when you hit the accelerator on a hill.