I would love to have some help to figure out why my boost fluctuates so much and the truck is underpowered. I can hear it in the exhaust when empty or loaded, but the power fluctuation is most apparent under load with a trailer behind me. It has been going on for about a year, and I am wanting my old unstoppable LBZ back. The truck is duel straight piped so the difference in sound when the power is fluctuating is easy to hear. The fluctuation is not that apparent without a trailer, so I have put off figuring it out for some time, but I just went to moab last weekend and was frustated with the loss of power. I have efi live now and logged my truck in fifth gear climing a hill. I was hopping someone could look at the log and point me in the right direction. The truck is set to stock-- only have straight pipe, intake, blocked and fingered and pcv reroute. I would be very grateful for any help!! I did end up with one code at the end of the trip--P0234 turbo engine overboost, but I figured that was just from so much fluctuation.

when mine was doing that it was because a leak developed at the joint between the intake elbow and the grid heater pipe.

I was just reading another thread on here about some guys with similar symptoms. Try checking your vane position sensor and solenoid. It sounds like your turbo vanes are doing some fluctuating, raising and lowering your boost as it wants. It could also be a plugged fuel filter. Just a thought, I hope you get it straightened out.

Thanks for the help!! It's been doing it for quit some time now and I have been through a few fuel filters as well as installed an air dog fuel system, so i'm sure its not the fuel system as my fuel pressure stays consistant with desired. I have also been reading about the vane sensor\selinoid, how would I check for proper function of these?

No Codes? It should show a fault in function on Tech2 or EFI on that surging if your boost tubes are tight and no holes in that drivers side one. Check for leaks it's a little leak that causes such a headache at times had one on mine loose clamp and finally opened a bit.

I brought my truck to a diesel performance shop here in town to see if they could nail down the problem, I will post the results he finds. Thanks everyone for the help.

I would also check the intercooler pipes where they are connected to the silicon hoses. My boost fluctuated when the one on the driver's side top by the turbo started slipping out of the silicon hose. Cleaned, used some hairspray to keep it from slipping and have not have the problem since.

I still have not been able to figure out what my problem is. I am scanning with efi live, but am not sure what to look for. My vanes are opening and closing very fast and that is where i get my boost problem, but I see that the computer is commanding this too happen (vane position is following commanded). When I am logging i see the vanes variate, the maf, map and EGR valve(when enabled) all fluctuate at the same time (like in concert). What is telling them to do this? Is there certain pids that I should be watching to figure out what sensor is commanding the variation? I know I can figure this out with EFI live, I'm just not sure what to look for. Any help is appreciated.

any news on the issue?

I'm hoping to have something figured out by this coming weekend. A friend of a friend that is a gm tech and efi live "junky" is coming down from boise to visit. He is gonna help me. I have some more input though, I took my blocker plate out and this seems to help a lot. Don't know why but if I have it out my boost is pretty stable and about 2 psi higher. As soon as I disable it with efi live it goes back to the way it was running. I will keep you posted.

What did you end up finding? Did a search and found this thread as my truck has begun dumping boost when pulling hills only to recover quickly. Not sure what is causing this. Very annoying!

What did you end up finding? Did a search and found this thread as my truck has begun dumping boost when pulling hills only to recover quickly. Not sure what is causing this. Very annoying!

When my LBZ was doing this it was because of a leak at the joint between the grid heater pipe and the intake manifold. Turned out that one of the two bolt holes had stripped out and was missing the bolt. I put a heli-coil in place of the damaged threads, along with new gaskets for the grid heater pipe. Tightened it all up and no more leaks. Steady boost pressure is a good thing!

Leak was easy to spot because there was black sludge all over the area where it was leaking from.

When my LBZ was doing this it was because of a leak at the joint between the grid heater pipe and the intake manifold. Turned out that one of the two bolt holes had stripped out and was missing the bolt. I put a heli-coil in place of the damaged threads, along with new gaskets for the grid heater pipe. Tightened it all up and no more leaks. Steady boost pressure is a good thing!

Leak was easy to spot because there was black sludge all over the area where it was leaking from.

Not able to find a leak anywhere so far. Any other ideas anyone?

I had a problem with mine with the turbo vanes cutting out when the computer went into closed loop when it warmed up to around 180 degrees and I would have no boost for about 10-15 seconds until the computer was able to recalibrate. I also had an annoying boost pulse around 25-28 psi of boost and the throttle rolled to around 3/4 throttle.
This all started when I switched to EFI tuning. The VGT vane problem was corrected by unplugging the EGR valve. EFI had it turned off but for some reason having it plugged in caused the vanes to cut out. Blocking the EGR off had no effect on the turbo surge at 25-28 psi of boost. This was in the EFI programming and was also corrected with a software update.
Question, I did not have to install the finger kit on my LBZ, EFI should have your EGR system taken care of, is the finger stick possibly causing a problem now with the MAF sensor? Has it always done it and did you have problems with a CEL and had to put the finger stick in when you blocked the EGR pipe? You said you had MAF,MAP and other sensors switching in rhythm with the turbo pulse. All of these sensors do work in rhythm of each other and all control fuel rate, timing and boost. Some are saying that there might be a possible leak and this is also true. A ruptured intercooler? You don't have it in your signature but do you use a K+N air filter or similar? Possibly a contaminated MAF sensor? You said you recently added a FASS system with no improvement so would say to rule out fuel delivery pressure. How many miles on the engine? Possible return line pressure problem due to bad injectors? I.E.: not holding rail pressure even with good fuel delivery. Bad MP3 pump?
Finally, there is an updated MAP sensor for the LBZ and others. If yours is stock, check your part number. The new one is: 12623671

Lots of possibilities....sigh....

I'll have to check my MAP sensor when I get home. infamus14u what did you end up finding?

Certain methods of disabling EGR in the tune cause this vane fluctuating. I had this issue with HpTuners. Changed the EGR settings in the tune and it went back normal.

Could this be caused by the Fingerstick? I recently deleted the cat and got some codes so I ended up putting in the fingerstick to get rid of them and now this issue has shown up.

Certain methods of disabling EGR in the tune cause this vane fluctuating. I had this issue with HpTuners. Changed the EGR settings in the tune and it went back normal.

What settings did you change? Having the same problem. Thought it might be the relationship betweed desired vane position and desired boost.

On Hp Tuners, it was the "master" egr disable feature. I enabled this like stock, and just set the enable and disable EGR coolant temperature tables out of range. The egr valve still opened, so i just unplugged it and turned off the codes. I can't be any more help since i dont have EFI live, but i think it may be you EGR settings causing the surging if you changed them.

I still have not figured out the boost problem with my truck. I have had a couple different people with extensive knowledge try to diognose the problem with no luck. Both people tell me the same thing, they start listing all the possible things that could be causing it, which is about 10 different things. I'm not gonna just start replacing parts and spending money, I'm sick of it! My fix is to sell the truck and get a new one. It makes me sick to my stomach!

So have your EGR settings been modified in the tune?

Does any one know if this can be caused by the fingerstick? I have not blocked my EGR but have put on fingerstick because of codes I was getting after doing cat delete. Now I have this fluctuating boost problem. How does a guy go about diagnosing this problem?

I had similar symptoms a few years ago. It was the down-pipe rubbed a hole in itself and the up-pipe. Check all exhaust mating surfaces.

infamus14u did you ever get your problem fixed? What was it?

Could a weak FPRV be causing this issue?