Pictures of Big Shots

VGT Turbo quick check

Before we get further into EGR guts lets jump into Variable Geometry Turbo for a sec. This is pretty amazing piece of modern technology which started living under our hoods right with EGR system back in Oct-2002 and till Jan-2007 was actuated by… air. The actuation itself was causing a lot of problems so they went to electric actuation by then. VGT is the mother of ISX power and efficiency unfortunately married to EGR who is the smoking father – so it gets screwed and whole family have problems. Theory of the operation is perfect though as when turbo gets closed (they call it 70% position) it builds boost momentarily so we have no turbo lag and no smoke from the stacks (EPA is glad) but next thing we want right after it hits its speed limit at 90,000 rpm (which doesn’t take very long, maybe a second) is to have it open (all the way to 20% position, mostly around 34% though) so the restriction on exhaust gasses is down – that’s where the sliding nozzles are doing their job, in the hot part increasing/decreasing backpressure. These turbos are greatest improvement on diesel motors since DDEC but like I just mentioned they get screwed by soot that make them blow because all this stunt with super-fast actuation only works when it works perfectly and having quater pound of coal all over the precise mechanism make it not so perfect anymore. Anyway, if you noticed your boost/pyro started acting strangely here is first, simple and inaccurate but totally free way of testing your VGT:

1. This is normal position when engine is shut down. The turbo is “open” by the power of spring inside of the actuator.


2. Now if you put some force and turn the wrench up you should be able to overcome the spring and manually “close” the turbo. The trick is to figure out if there is some additional (beside the spring) friction coming from the soot or whatever else that shouldn’t be there. I was never able to feel it taking this shot coz my turbo was and still is good so no further advices. I was told about this method by mechanics from a reasonably big ISX fleet.



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