Hey guys this is kinda long so thanks in advance..... I have a 2007 F350 CCSB Auto 4x4 with 113xxx miles....I recently got the PO299 Underboost code and this damn turbo is killing me so please help!!...my symptoms are minor:

turbo surges when cruising at a steady speed, whether its 25mph or 70mph...the boost guage (I know its not 100% dead on accurate) goes from about 7 to 10 psi on the highway and when i am driving down a side street at 25mph it will jump between 2-4psi...i should add the RPMs surge as well, but very little, maybe a hundred if that RPMs...it is so annoying to hear the engine and turbo surging as I am driving cause its obvious, and even more annoying to see that damn CEL on my dash! and I dont want to just tape over the light, I want to fix whatever the issue is! (my buddys advice)

Other than the surging and obvious engine tone changes when the turbo surges, nothing else is observed, turbo still spools to about 27 PSI and it runs fine otherwise....no smoke, no coolant puking, no turbo lag or farting, no long start, no leaks, no other CELs....

I researched on many forums and started out simple and changed both the hot side cac tubes/hoses as well as the cold side tube after inspecting them they looked pretty crappy...I then cleaned the MAP sensor/port as well as the EGR valve(was very dirty)inspected air filter which was fine, that didnt fix the issue...I then took the turbo off, inspected it and cleaned it up nice, rebuilt it with all new o rings, gaskets, 360* thrust bearing, bearings etc...I left the impeller, U ring and vanes on as they appeared to be fine and moved freely...one of the old bearings on the hot side was visibly worn a little but nothing crazy...also cleaned the EBP sensor which was actually pretty clean...none of this fixed the issue....

I went ahead and bought a wireless OBD scanner (great tool) and bought 'Forscan' app on my iPhone to monitor everything and read the engine codes more in depth...I noticed that when the turbo surges, whether it be on highway or side street, my EGR voltage, VGT solenoid % as well as my ICP is surging as well...not sure if this is simply a result of the turbo surge or the cause of the turbo surge...how can i test my VGT Solenoid?

Let me also add that at idle im at 85% VGT and at times it will jump down to 15% and then back to 85%, at which point u can hear the engine tone changing...I understand that happens so the turbo doesnt stick and it does that every once in a while at idle, but should the VGT % jump around like that? I am thinking of inspecting my ICP sensor as I read that a dirty or bad one can cause surging...not sure what else could be causing this issue, as I also put new fuel filters on last oil change...I thought for sure cleaning the turbo would fix it but apparently the turbo wasnt sticking from being dirty cause it was cleaned up...

What tests should I run or what should i pay attention to on my Forscan app?...my FICM power is right where it should be at 48-48.5, my EOT and ECT never go above the 15* difference...I can monitor all types of things on Forscan so please shine some light...if it is a bad VGT solenoid I was thinking of just waiting to buy a whole new turbo instead of spending 150$ for just the solenoid when 750$ gets me a new turbo with solenoid anyway...or maybe buy a reman one from ebay for 50$ and pray? (UPDATE I bought one for 50$ I will see if this works if not I will send it back)

what do u guys think? could it even be a bad EGR valve? no symptoms of EGR failure either...the Forscan app says it could be a bad EBP sensor (inspected and cleaned it already) or VGT controller...thinking of bringing it to a well known 6.0 diesel shop thats close by, but they charge 200$ just to diagnose it! may be worth it tho but I want to figure it out on my own...Thanks!!

Steve

UPDATE - A member on another forum suggesting unplugging the ICP sensor to see if the surging goes away, and I read on another thread to unplug the EGR valve while it is closed to see if the surging stops.....

 

Check your fuel pressure. Check for a post called boost problem by will byte had similar problem and it needed up being a fuel pump

 

You are on the right track. It could be one or more of many things. Sneaky problems sometimes have sneaky causes.

ICP and IPR would be my next suspect. IPR is commanded. Many people prefer to watch ICV as actual, ICP in psi is computed. ICP sensor is sensitive to oil in the plug and sometime leaks its self. The pigtail seems to deteriorate quickly also, especially if there is oil present. Un plugging the ICP is a valid test, it will run on default values and you can see the voltage change in three steps as rpm increases. Remember to check the connector and pigtail for oil and shorts before testing, it's still connected to the circuit even with the sensor unplugged.

Remember, the VGT % is a command also, not a reading of what it's doing (actual). The turbo may be doing what it's told if your seeing the number bouncing around.

The fuel pump or even the pressure regulator could be an issue as FiznUKa said. There is no sensor for that so you'll need to come up with a gauge. You will need a metric M12x1.5 to English adapter (Most gauges are 1/8" NPT) to get a gauge set up going. I ordered the adapter online and got the rest of the stuff from Tractor Supply and Lowes for mine. If you haven't put a blue spring in the regulator yet, this would be a good time. If the pump becomes suspect it is available separately and quick/easy to change. Don't buy a complete HFCM unless you need it.

A/C current on the power caused by failing diodes in the alternator will make these trucks do odd things sometimes.

Last thing I can think of is to monitor the reference voltage (VRef) it should be 5vdc or very close to it and rock steady (once the battery voltage settles down after a start). This is the power to all the sensors from the PCM. This circuit is common to all the sensors so a short anywhere will affect all of them and can cause a quick brain cramp to the system.

 

FiznUKa and Axelrod thanks...I read Wills post in its entirety boy was that thing long but filled with good info....Axel I certainly hope its something as easy as the ICP sensor itself or the pigtail, IPR costs some decent coin!as does the fuel pump but at least its worth the money to fix this damn thing once and for all! I will check the ICP sensor tomorrow and see if unplugging it works...I will check Forscan for the VRef...not sure if I remember seeing that but there were a ton I bet its there...

any chance I should drain the HFCM? Maybe thats clogged up? I doubt it but havent drained it in a few months since my last oil change/fuel filter change...guess its worth a shot...I will also check MAP BARO and EBP while in KOEO as I read in Wills thread they should all be ambient pressure...then again check at idle and under accel...I will get back with those! thanks