Hard Boost Cut to hard for the engine?
 

On a cold monday, I was driving on the onramp of an highway. Just before I wanted to shift at +3500 rpm to an higher gear - BAM - hard boost cut kicked in. The ECU didn't like a little boost on the colder engine and it cut all fuel and ignition. The car quickly decelerated and cached up again when the 1/4-a-second boost cut algorithm stopped. This sudden change was very hard on the car. it developed a grinding noise right after. At first I suspected the driveline. Gearbox OR diff.


Hear me ( use headphones)



Since the noise was only around under acceleration and a little boost I thought it was either bearing noise from the Gearbox OR diff, not engine related.

So I drove it a few days to work and back, knowing not to go into boost. It drove fine, did not feel a thing!

This is the sound again from the driver seat:






I asked a few people around FB groups and they all said it could be the driveline. none of them suspected the engine. I had the idea to make one last video, just to hear the sound again.

This is what happend:





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Rod knock...


So this story made me believe hard boost cut did more than it could save. Anyone had similar story's?

Q1: Anyone thinks the previous sounds are related to the engine developing rod knock?

Q2: Could hard boost cut be this bad?

Q3: Why did you go into boost while the engine was cold?
A3:

What ECU are you using?

Cold engine means poor lubrication and loose piston to wall clearance. Pistons rock in their bores more. Oil is not being slung onto the cylinder walls as well as when warm. Oil is thicker and often bypassing back to the pan through the relief valve instead of going through the engine lubricating parts. Oil pressure is up but volume is way down.

Your cylinder pressure may have possibly spiked during the cut but it is unlikely. It probably had a problem with lack of oil flow and high cylinder pressure due to boost and load.


Don't ever put a strong load on an engine when it isn't up to operating temperature.

ME221

I don’t think the boost cut killed your engine. Even though it is an unpleasant experience, overboost cut is there to save your engine. What was your boost cut setting?

I am also doubting whether you actually have rod knock or you bent a rod.
Usually a rod knock is very audible at idle as the oil pressure is low, with some revs the knocking usually decreases as the oil pressure increases.
Your sound gets much worse with revs, making me believe it could also be a bent rod hitting something.
Maybe you already had a bent rod after the boost cut and made it much worse during the pull.
I would say: pull the motor and check if you spun a bearing or bent a rod.

Rod knock often increases in intensity with piston speed.

What do you guys think of the cracking/ metallic sound in the first two videos? Is this the a forerunner to bearning fialure or a bend rod?

Seems there was a boost issue. I checked dashcam footage. Boost went 1.2 bar / 17,4 psi and boot cut tried to save the engine.
That didnt kill it... but bent the rod slightly, and gave a wierd noise above 3.5k rpm and on boost.
After that I drove it softly around not knowing the open loop boost control was disabled or defective. Yet I though the transmission was going bad and tired to find the sound by making a lazy 2nd gear pull.
After that pull; The ticking sound was the bottom end of the piston hitting the oil squirtes probably.

Unfortunate.


1, 2, 3, 4. left to right.

Shall I upload the last map if interested here?



The Rod bearings where still in once peice and only look used.
The Cranksaft has little scars allround.

Thanks for posting the update, maybe I should consider a career in fortune telling rather than engineering.
Now is a great time to upgrade the rods, if you are in a rush getting the engine together, I have a set of forged rods laying around.

More info on those rods you have laying around?

Banana rods.. good times

"Slightly", LOL. Glad the damage was localized with no other casualties!

Where was boost cut set on ECU?

It was set at 220 kPa / 1.2 bar of boost or 17,4 PSI