Anyone seen this rant on the DS4?

[WarWagon]

I am curious as to why this simple engine has a mucked up program. What is the quality level? What is the pass fail criteria: Stalling? Going all Toyota on you?

Does management not have the skills to test the programs other than driving the prototype vehicle?

Well at least the diesel doesn't go all Toyota on you - most of the time that is unless a PMD dies just right...

Under the gun for emissions is not leaving much room for program testing each model year.

Some GM gas engines have major issues including the corrupt memory Duramax engine will not start recall.

From what I have seen with a specific GM gas engine: GM and other companies simply don't care. Seen what the only watchdog they have does and they don't care either.

Have a defect in the factory program and you are SOL. Unless it starts killing lots of people.

 

[Matt Bachand]

I would have to guess someone with 'some' programming skills in house made these programs instead of them hiring/subbing a true professional computer programmer to do the job.

Of course if the best guys are doing the work, who's going to check it for errors or efficiency?

 

[SmithvilleD]

Isn't his point on EGR, that you need to take into account how disabling/changing EGR changes peak cylinder pressures & the timing of the spike?

 

[WarWagon]

"Excessive NOx indicates excessive cylinder pressures - pressures above the design rating of the engine."

:icon_bs:

It indicates high combustion temps where nitrogen is reacting with oxygen. It does not indicate you are popping head gaskets with over design limit combustion pressure.

A gas engine peaks the NOX during light throttle and lean mixture. Hardly peak combustion pressure. Maximum torque is from peak combustion pressure and you need heavy/WOT throttle to get peak torque. Usually EGR kicks out at WOT.

Yes it changes things on an engine but not to the melted slag presented.

 

[SmithvilleD]

Maximum torque is from the highest mean cylinder pressure over the most effective crank angle. This is related to peak cyl pressure, but not necessarily the same thing.

Diesel's typical peak cyl pressure typically happens well ahead of the most advantageous crank angle.

I'm not trying to support the article's viewpoint that EGR shouldn't be modified/eliminated. Just pointing out EGR's impact on cylinder pressures. Cyl pressure is directly related to cylinder charge temps.

It's not that uncommon to hear from Duramax/EFI Live folks that got too aggressive with cruise/light throttle timing chasing fuel economy improvements, that found the practical limits by head gasket failure.

 

[SmithvilleD]

Prolly should clarify a bit further. The problem regarding part throttle timing & head gasket failure occurs when injection starts so far before TDC that the growing combustion heat/pressure combines with mechanical compression still increasing as the piston approaches TDC.

It's not uncommon for injection to start significantly before TDC. The trick is finding the best compromise to highest mean torque production.

The amount of cyl pressure increase before TDC that's due to the beginning combustion is in effect - negative torque. It's not uncommon for OEM timing strategies to have some combustion happening before TDC. Just have to keep it very limited to avoid peak cylinder pressures happening at/around TDC, as that pressure/temp has to be contained for significant time (as the crank rounds TDC) before crank angle gets to the point that pressure/heat can be exchanged for work.