Engine/Transmission (1998.5 - 2002) 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 trip over the weekend that my boost pressure would do something I cant fully explain. For anyone who may not know my driving style, I generally dont pull a trailer 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 by doing so 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?

 

[SAndreasen]

Hotter air from the outside and underhood temps causing air to expand and raising psi? Maybe but i don't know

 

[KATOOM]

At this stage of guessing, I'm going with the possibility that either the engine entered a different fuel map or that the impeller became that much more efficient under the extreme heat and allowed a slight increase in boost.

 

[SnoKing]

You still running the small OEM HY35 turbo? There are turbos that will move more air and still respond similar the the HY35. I installed a PDR35-12W on my 2001.5. Chris

 

[KATOOM]

The HY came in the 2001-2002 automatic transmission trucks. Also found in some 2000's depending on build date. I'm still running the stock HX35.

 

[SAndreasen]

I didn't read the original post again but one time on a trip Washington my boost came up a few psi I think do to a huge drop in elevation it only happened once but that's the only thing I could come up with ? I have my chip set to limit the egt to 1250 and it sticks within about 10 degrees of that limit no matter what I pull . Now my old gen one I use to burry the pyrometer passed 1300 and leave it that way for miles towing was it a good idea probly not but then I here people say 15 is ok and maybe it is because the gen one was still running when I got rid of it

 

[SnoKing]

The HY came in the 2001-2002 automatic transmission trucks. Also found in some 2000's depending on build date. I'm still running the stock HX35.

Yep, missed the 5sp part. Snoking

 

[KATOOM]

I didn't read the original post again but one time on a trip Washington my boost came up a few psi I think do to a huge drop in elevation it only happened once but that's the only thing I could come up with ? I have my chip set to limit the egt to 1250 and it sticks within about 10 degrees of that limit no matter what I pull . Now my old gen one I use to burry the pyrometer passed 1300 and leave it that way for miles towing was it a good idea probly not but then I here people say 15 is ok and maybe it is because the gen one was still running when I got rid of it

I have to admit that I'm surprised how many times I've heard of people holding firm at 1300*+ EGT's on the hills. Still something I cant come to grips with.....or maybe I have little faith in my pyrometer.

Yep, missed the 5sp part. Snoking

No problem, just pointing that part out.