I know I have alot of threads and really didn't want to start another one, but I believe it will help a lot of members get there trucks running better stock or performance.
So VGT actuator what is it and what does it do? the actuautor sits on the side of the turbo and actuates the vanes in the turbo using oil pressure from the low oil pump. The command for the VGT actuation comes from the ECM in a electrical signal, which is why the VGT actuator is also know as a hydualic electrical actuator (hydroelectrical). Hydraulic for the oil part that moves the acuator and the electrical for how it gets it's command.
The command from the ECM is very inportant on the way the performance of the turbo, and the way the truck runs. If there is a signal loss then the VGT won't move anything, if the vanes get stuck and the actuator can't move them then you are stuck with a non vgt turbo. Depending on the where the vane position the vanes are stuck in depends on what kind of non vgt turbo you have. The Idea behind the VGT vanes is to give you a small turbo to take off on (closed) and a big turbo when at wide open throttle(open), and any where in between depending on the load of the engine is under. So if vanes are stuck open then you basically have a big non vgt turbo, a lot of turbo lag(smokey) until the turbo is getting enough air from the exhaust to drive the turbine wheel, then will run good until the air is being restricted by the vanes and turbine wheel stays in the speed the vanes let it. If vanes are in closed position then the turbo will act as a little non vgt turbo, little lag and fast spooling but boost will not build since the vanes are limiting the air flow, then the truck will start to smoke, too much fuel not enough air.
Sorry for the long explaination, but gives you basic idea, and yes if you get to small of a non vgt turbo it will act as stated above, and if too big same as above. So picking the right non vgt turbo for the fuel, and performance you want is alot of trail and error, or experiance of other that have tried it. There is a lot more to just size of the non vgt turbo compressor size and matching the turbine housings a/r but that is not what this thread is about. What the thread is about is what to do to make sure the VGT turbo works right, no surging, good boost, and fast responding, not just for performance turbos but stock also.
Tuning the VGT turbo is just basic maitaining maintenance of the truck. All the sensors need to be ceaned to make sure the ecm is getting the correct information that it needs to give the VGT commands. The EBP sensor, located on drives side next to oil dip stick tube with a electrical connector on it. It is used to measure back pressure of the exhaust and reports to the ECM. lines and fittings need to be clean, no soot, carbon, and no restiction in the lines or fittings leading from exhaust manifold to the EBP sensor, remove fitting and make sure it is clean and no carbon deposits. Next remove and clean your IAT sensor or sensors depending on year of truck used to measure air flow inside the intake manifold, reports to ECM, but they all have the one at the drivers side manifold at the top of the runner. It will have two wires and connector going to it, remove it and clean it, it should look like a little cage around a copper bulb, it doesn't and looks like a solid piece then it needs cleaned. The last thing to check is the MAP sensor and lines, fittings. It is located on the passenger side of manifold on top, has a fitting coming out of the top of manifold and a piece of hose that goes to a plastic sqaure piece by the fan motor for the heat aircondition system. It will have hose on it and then a electrical connect on it. It measures boost and gives a referance for the ECM, the hose must be crack free same length if repalced, free of carbon. Remove the fitting and make sore that it is clean and free of anything inside of it. You can use a wire or same sized drill bit to along with solvent to clean anything in it. Also make sure there is nothing in the manifold the could be plugging the fitting.
Lastly clean the MAF sensor or IAT senor located at the intake tube near the air cleaner box, and has a electrical connector.
After everthing is cleaned then your truck is ready to run, and give the correct infomation the ECM needs to command VGT actuator. You should do this ever so offen I have seen a lot of rubber hoses cracked and split for the MAP sensor at the manifold, so it should be checked more often. Keeping everthing clean will help the truck to run right, and it a aftermarket turbo is installed it should be first thing done before installing the turbo. Hope this helps everyone and keeps their truck running good.