WOW, Wish I would have....
...purchased the right truck the first time. First run today with new to us GMC 3500 and WOW. The difference between the GMC and F350 is night and day. Truck pulled our fiver over same hills that o...
Forum Discussion
Engineer9860 wrote:transamz9 wrote:BurbMan wrote:jus2shy wrote:
The unison ring is what synchronizes all the guides/vanes on the turbine side of the wheel. These guides can close to add more velocity to the exhaust gases allowing the turbo to spool up sooner and higher. The vanes can also be opened to allow for more exhaust flow while maintaining optimum pressure. These rings can be cleaned, lots of youtube videos on how to take care of that. It is these guides/vanes that allow the turbo to be called a "Variable Geometry" turbo. Without this ability, you'd have to settle for either low-end grunt or high-end power. Variable Geometry gives a turbo far more operating range. Hope that makes sense.
Thank you, that makes sense. So if the EGR cooler goes, you get coolant in the intake which in turn causes the unison ring to rust, which in turn impedes its ability to vary the turbo geometry, which in turn limits the turbo's effectiveness over various RPM ranges, which in turn causes a general power loss? Do I have that right?
Yes which will then cause an "overboost" or "underboost" condition that so many people talk about. An overboost condition sends the motor into limp mode.
The 6.0L that I drove didn't go into limp mode per se. When the turbo would overboost it would blow the CAC hoses off. Sometimes so violently that you could see the hood lift. The mechanic at the Ford dealer told me he had seen them dent the hood from the bottom on extreme cases.
HAHAHA!!! It scares the stuff out of you when it does it too. I have not seen the tube come off because of an overboost condition though. It's 99% of the time not getting it put back on correctly with the correct torque. If reusing the old boot you almost have to clean it really good with a degreaser ( I use brake cleaner) and then go to the wife's hairspray stash and spray hairspray on the inside of the boot where it clamps onto the turbo. If you notice when you get a new boot it is sticky on the inside. LOL! My company truck has a dent in the hood from underneath just like you stated.
My truck has been in limp mode more than once because of an overboost. It doesn't take much to get an overboost code and I have seen buddies pin the 40psi gauge on the dash with tuners and not blow the factory tube off.
