Strange boost bumped up with higher EGT's.....

[KATOOM]

For those who may have an answer.....

 

I recently noticed while on a long hot highway camping adventure over the weekend that my boost pressure would do something I cant fully explain.  For those of you who know my style, I generally dont pull with very hot EGT's.  For me 1200* is HOT and I prefer to stay under that temperature just because it keeps the engine temperatures happier.....and its just really hot in my opinion.

 

Nonetheless, grossing about 22k pounds, I was pulling hard up some long grades and because of the immense summer triple digit heat it was hard to keep the EGT's from climbing up to the 1200* range under heavy throttle.  Not really wanting to slow my speed down too much I tried a couple times to hold firm on the throttle and let the EGT's get to 1250*.  But what I noticed both times I did this was as soon as the EGT's reached that 1250* mark the boost strangely jumped up 2-3 psi.  Not just on the gauge either as I could also hear an audible difference in the turbo. 

 

Does anyone have a logical explanation why this happened?

 

Edited August 2, 2016 by KATOOM

[TFaoro]

Higher temperatures means more energy is going through the exhaust turbine, but I wouldn't think you would see a sudden jump.

 

The only thing I can think would cause a "jump" is something with the wastegate, or the truck moved into a new part of the fueling map.

[KATOOM]

I thought about the fueling map too but wasn't sure if the sudden increase seemed viable.

[Me78569]

Do you have any tuning in place?  

 

I see the ez now

 

 

So it could be that you are reaching a new level in the load scale and the ez is demanding more, and or changing timing.

 

did the truck pull harder?  or did boost just jump with no other change?  

Edited August 2, 2016 by Me78569

[AH64ID]

A hot turbine is a more efficient turbine; however, it shouldn't be that noticeable or sudden.

 

What was the coolant temp doing? Could a ECT change have caused a timing/fueling change?

[KATOOM]

The only modifications I have is the EZ and 275's.  Injectors installed about a year ago.

 

ECT was around 215*.

 

Whether or not the truck pulled harder during the boost bump, I cant say.  With that kinda weight behind you its difficult to notice much since things dont respond too quickly other than the pyrometer needle.

 

 

[Me78569]

I understand.

 

IAT temps may have come up and then ecm may have changed the fueling command.   There are numerous sensors that play into the fueling map, so I would guess that it is "normal" haha.