2012 Prius 120k miles diesel sound when slowly accelerating

What exactly do you mean by "dieseling" ??

If it is an exhaust sound, then have the exhaust checked.

If it is a knocking sound in the engine like the OLD diesels used to do.......then you should STOP driving it and have a shop check it out ASAP.

 

Get circuit clogged

 

You are exactly at the point where plugs are supposed to be replaced. And, yes, have a shop check for other problems.

 

Egr circuit

 

My husband and my older friend tells me that in old carbureted cars, carbon build up in the cylinder heads would lower the volume and raise the compression in the cylinder and cause "preignition" in cheaper lower octane gasolines that have lower ignition temperatures. Octane, fyi, is the quantitate measure of the percentage of eight carbon linked gasoline molecules in the chain, as opposed to heptane (7) and hexane (6).

In newer computer controlled cars, an "anti-knock" piezoelectric sensor senses preignition and retards the timing to alleviate this condition.

In today's engines with direct fuel injection, where fuel is directly injected into the cylinder and with blow by oil laden and moisture from exhaust gas recirculation (EGR), carbon buildup in the cylinder head is accelerated in older higher mileage cars.

There are several well read threads on EGR cooler, EGR valve and intake circuit cleaning. Oil catch cans also help in this matter.

 

Cleaning

 

Do you possibly mean a metallic “pinging” sound coming from the passenger side of the engine compartment? Kind of a fairly rapid “tink, tink, tink” or “pink, pink, pink” sound that seems to closely track with engine rpms?
If yes, you may have classic pinging , which is a form of pre-ignition where the fuel-air mixture in the combustion chamber will ignite in a quick rush rather than burning in an even wave along the flame front as it is supposed to do. The result is an uncontrolled, too-fast combustion that is closer to being a mini-explosion, and that explosion pops the valve suddenly onto its seat rather than its normal gradual, graceful descent into the seat. The “ping” or “pink” sound you hear is the sound of the valve hitting the valve seat.
Octane measures how smoothly the gas/air mixture burns under high pressures and temperatures, so low octane gas is more likley to ping. Pinging will depend on the throttle setting, engine load, mixture rich versus leanness, and the degree of the ignition before Top Dead Center (TDC) . The 2012 Prius engine has a “knock sensor “ that detects pinging, at which tume the ECU will retard the ignition timing to help eliminate it. Nevertheless, consider purchasing higher-quality gas, higher octane gas, or adding a good quality combustion-chamber cleaner additive to your gas at fill up for several tanks. That additive will help if one cause of the pinging in your engine is combustion chamber carbon deposits, as these deposits preserve enough heat from one combustion to the next that they tend to trigger the premature burning or preignition event. Hope this long winded answer helps!
(Diesels ping like this usually at idle due to the much higher compression ratios in diesel engines, but those engines are built to take those stesses whereas gasoline engines are not.)
(More shortly: what Georgina said!!)

 

Most classic Otto gasoline engines are set so that the spark ignites at six degrees before top dead center in the compression stroke. Retarding the timing ignites the fuel air mixture, before pinging occurs.. This achieves ignition before self ignition occurs. Retarded timing has the effect of reducing power.

 

Have you checked it for codes?

 

Why don't you just come right out and describe the noise without comparing it to a diesel engine ?

IF there is a knocking noise in the engine under "normal" acceleration, then you could have a SERIOUS mechanical failure developing.
It is possible that some bad gas could cause it........but that is rare and gambling on that being the cause might be a BIG mistake.

Have you checked the level of the engine oil ??

 

By definition, PREignition occurs BEFORE the spark hits. Therefore retarding the spark timing does NOTHING to prevent that.
But that is a common misconception.

 

Retarding the timing means to set it at more degrees before top dead center (BTDC). It does not mean igniting the mixture later. It means igniting the mixture at a lower compression and before compression self ignites the mixture.

The real answer is to remove the lead and to mechanically clean out the carbon buildup.

 

If the fuel injectors are not creating a mist because they are dirty and/or clogged, you'll get preignition
because not all the fuel is burned during ignition. It won't matter what the timing is set at.
It is probably a clogged egr cooler and related parts.
Like all of said, clean the egr parts, intake manifold, change the pcv valve, change spark plugs, and install
a catch can. That's a good start....

 

Your intake manifold and egr cooler needs to be cleaned

 

Absolutely, positively and completely WRONG.
You have it exactly backwards.

 

And that is not an accurate description of "pre-ignition" either.

It might create "post-ignition".......or backfire.

 

I may not have the great scientific mind you have, and may not be able to explain in such great scientific exact ways
that you apparently have, but the fuel ignites from the heat BEFORE the spark ignites it.
That's where the phrase "pre ignites" comes from. It certainly is not post ignites.
Or do you have a scientific explanation for it?