Engine/Transmission (1998.5 - 2002) Help understanding Boost and Fueling.

[rjrkihap]

I'm still having a bit of trouble grasping this concept. Any help will be appreciated.



1. I only see a max 18psi of boost ('99 with Auto). I have been told wastegate opens at 20psi. Therefore, can I assume the following: A. My wastegate has never opened. B. The computer de-fuels at 18psi.



2. If the computer de-fuels at 18psi, will a boost fooler prevent the computer from de-fueling? If so, will the new found fuel raise my boost to the 20psi causing the wastegate to open? And finally, if I added a boost elbow/J-hook, how far will the stock fueling raise boost.



Now, if my reasoning is wrong, please help me understand what is happening at the 18psi and what would a boost fooler on a stock truck accomplish.



Thanks



Ron

 

[PC12Driver]

The wastegate opens at about 20 psi at the compressor. And it's not an open/close thing - it's progressive. So it may start to open at 17 psi and be fully open at 21 psi. How far it opens depends on how much energy you have in the exhaust (fueling/rpms). There will be some pressure loss through the intercooler and plumbing before it hits the intake manifold as well, so 18 psi on the gauge is about right when things are working properly.



If you're truck was defueling (which happens if boost reaches the low 20s in the manifold, which you don't have) you'd get a check engine light and an overboost code. And as I understand it, the defueling is pretty dramatic. You're not there, don't worry about it.



An elbow would gain you a few more psi on a stock truck (maybe high 20's?) which would result in slightly lower egts on the top end and no noticible power gain (air is cooling, fuel is power). And in order to run the higher boost without setting a code and defueling, you'll need some sort of electronic boost fooler or a box with boost fooling built in.

 

[rjrkihap]

Thanks PC12, great explanation.

So basically, a boost fooler on a stock truck (with an elbow) will only provide more air (for cooling) and do nothing to provide more power (as the computer will not allow additional fuel regardless of what boost pressure information it is receiving from the fooler.

Additionally, de-fueling only occurs when the computer receives an over-boost signal. So the computer isn't automatically defueling when it sees 18psi, but rather as a safety measure because it sees 22+psi of pressure.

Am I getting this correct?

Thanks again

Ron

 

[Ken Roberts]

hummmmm......

FWIW, My 98. 5 wastegate crapped out when the diaphram got a hole in it. Ya can't just buy the wastegate assy, ya have to buy a complete turbo assy. So I bought a used turbo assy off another member. It was for a 99. I removed the WG assy and installed it on my 98. 5 Supposed to be the same. It was not. It would only make 12lbs of boost. No amount of fiddling would change it past 14lbs. However, an adjustable elbow and a Boost fooler did the trick. It will now spool to 28lbs. I can't seem to adjust the elbow or I would back it down to only make 20lbs or so.

Still cheaper than a new turbo assy.



YMMV



Ken R

 

[PC12Driver]

Thanks PC12, great explaneation.



So basically, a boost fooler on a stock truck (with an elbow) will only provide more air (for cooling) and do nothing to provide more power (as the computer will not allow additional fuel regardless of what boost pressure information it is receiving from the fooler.



Additionally, de-fueling only occurs when the computer receives an over-boost signal. So the computer isn't automatically defueling when it sees 18psi, but rather as a safety measure because it sees 22+psi of pressure.



Am I getting this correct?



Thanks again



Ron

Sounds about right...