Okay so after head gaskets and studs I cant get over 20psi unless im in overdrive and roll into it. Its the same on or off the SCT. It seems like at WOT it builds boost quickly to 20 psi and then just stops. When i roll into it in OD it will gain boost up to about 26 psi but once I mat the accelerator it seems to fall off back to 20 psi. could removing the turbo during the install have knocked some kind of carbon deposit loose in the turbo and stuck one of the unison rings or am i chasing a ghost boost leak. Is there a correlation between the VGT and the TPS? Ive checked all hoses under load and all exhaust connections under load and havent found a damn thing. I am stumped and so is the shop that did the work. All systems in the computer are commanding correctly and a turbo sweep test reveals no surprises. Im gonna pull the thing apart this weekend but this is got me bent out of shape 4500 dollars in and no closer to my horsepower and reliability goals.

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115 views no ideas huh?

 

There was a thread on here about a VGT relean sequence, from having the batteries disconnected for a period of time you might have to go through the relearn process, it involved cyling the key then drive, sorry I don't remember the process, someone stepped into a thread when someone else was having the same issue and posted the procedure, might want to post about the relearn procedure.

 

Thanks i will give it a google and then give it a try.

 

Despite what the gauge is reading, how does the truck run?

FWIW, when I roll into it I can get higher boost than that, but WOT on my race tunes usually results in about 20psi or so. It is less than stock when I'm WOT and RPM's are up. However when I roll into it I'm touching 35psi sometimes. You can't hear any leaks? What tunes have you tried?

 

truck runs like a raped ape. its just that i was seeing 27+ psi at WOT before head studs and now only seeing 20 at WOT. I want that boost back. Im gonna try somebody elses tune just for reference but right now i only have looney and looney nitrous tune and a stock egr delete tune. All result in very similar numbers. stock with delete is only peaking about 28.

 

Not to get too sidetracked here, but boost is a measurement of restriction, so it's kind of a silly way to measure it like we do. What we really want is volume of air.

So before you were seeing 27+, and now you see 28 on stock tuning?

Like I said before, I only see 20-22 WOT on my race tunes. The only time it goes above that is when it lugs a little (like when the TC locks up at highway speeds) and roll into it.

 

Maybe i just need to put the thing on the dyno and verify the HP and torque is about where i think it should be. WOT Stock tune without the TC locked up in OD i was seeing 25-27. Looney with the same situation was 29-33. Now the only way im seeing that amount of boost is rolling into it in either tune. Tried doing the VGT relearn today but i dont think the computer will run thru the test without a egr valve hooked up. Gonna borrow a known good egr tomorrow hopefully and try it again. The more you mention that your boost levels are where they are i feel like I maybe chasing a ghost.

 

I feel like you are too, especially if you can see those boost numbers just by rolling into it. That's the only way I see them too.

You're better off trying to run a 1/4 mile run and timing it and calculating off of your weight to get a HP reading. It will be far more accurate.