Boost vs. RPM

[DIGItonium]

This is weird, so bare with me.

Typically I can get about 5 PSI steady at half throttle around 3-4k RPM. It ramps up quick. Then it maxes out around 8-9 PSI steady around 6k RPM at full throttle.

Then there are times I have to flog it and can't get much power as if it is held back. In 2nd, the boost gauge slowly ramps up in sync with the tach to redline, but it doesn't max out at 8-9 PSI. It feels like the ECU is limiting the time to "fully" open the throttle, but limits how wide to open as well. I notice this after a warm start, and it gets a little better after a few minutes. Then there are times the "problem" comes back, and I can't get the car moving even with additional pedal travel.

I did get the brake switch replaced a few months ago, and I was able to get the car to scoot crazy fast in 2nd. Max boost picked up well before 4k RPM instead of ramping up slowly. The < 2k RPM slow pickup or hesitation is coming back. I recently filled it up with non-ethanol fuel, and it seems to improved response and reduced minor roughness at idle.

Just curious since I don't have a datalogger for turbo boost.

[EDIT] Forgot this might have to do with the ECU throttle tables. I'm still running the canned tune from GTM. My car never got dynotuned after the kit was installed. Possibly need updates to the throttle tables.

[Nixlimited]

Any boost controller? Sounds a little bit like it could be a sticky wastegate.

[tower74]

Or a leak...

[luigi90210]

check for boost leaks and fix any leaks, if that doesnt help then check the BOV for leaks, and if that still doesnt help, you might need new wastegates or turbos

[theDreamer]

Here is a link to Ron's post about his TT having some boost issues: Ron's better late than never journal.
Slightly different than yours, his was more idle but might be something to look at.

[Ron]

Sounds like a boost leak Digi.

[DIGItonium]

Thanks. Not sure how to check. I sprayed maf cleaner all over the place and don't see anything. I do notice a slight hissing sound around the bov area when it builds up boost. Think it's too loose or venting too early?

BTW this is starting to make sense in regards to slightly rough idle.

[DIGItonium]

Ok here's what I felt, and it's weird. The car did it again in which it wouldn't rev so fast as if I couldn't open up the throttle. At 3-4k RPM there wast no boost even with my foot to the floor. All of a sudden I felt and hard a faint clunk, and the boost jumps to at least 5 PSI. Throttle response returned, and I was able to get the car going fast as the pedal went further down.

Think something's sticky? I've felt this a few times.

[Chuck33079]

Maybe take off the throttle bodies and see if they're gummed up?

[DIGItonium]

Here's an interesting question. I think everything looks good, but now I wonder about my HFCs. I've had the F.I. HFCs installed brand new at the same time the turbos were installed. I'm pretty much past 30k miles with the kit and the HFCs.

Think the HFCs clogged might be the reason for the slow spool or slow revving? Also, maybe it's the reason for the engine dying at idle on startup at times?

[Chuck33079]

That's entirely possible.

[theDreamer]

I would definitely rip them off, even with my SC I blew out a factory cat after awhile, I really need to invest in some TP.
I know when mine blew I heard a slight rattle, almost like the clutch, from under the car when I would be in neutral and gave it a slight rev up to 1200.

[DIGItonium]

I think that's what I'm starting to hear and feel. Response is getting pretty weak especially as the cats are still "cold." It's a wonder why I smell fuel at times. All starting to make sense now. I couldn't get it to hit boost on the freeway again, and it was laggy.

Priorities is keeping me from making the full switch to 3", so I might have to get another set of HFCs. I can do TPs, but the smell makes me nauseous.

[Mitco39]

I am not to sure about the cats, unless the engine is going into a sort of limp mode because of them. A plugged or shot cat would not cause the engine to come in and out of boost like you are experiencing (unless of course the ECU is doing funny things because of it). Do you have uprev? a simple log would tell you exactly what is going on (if its not being caused by a stick wastegate or something similar).

[DIGItonium]

Yea, it's UpRev flashed with GTM's kit. I've not started having these funky issues till recently, and it feels like it is progressively getting worse. For the past several months I notice a faint whine which appears to come out of the passenger side turbo. The clunk feeling I felt from the lag sounded like it came from underneath on that side as well.

Also I wonder if this is why I've not been able to consistently get 8-9 PSI, and that I had to dial up the MBC a little bit the past few months. The boost gauge needle is steady, so it doesn't jump all over the place.

Exhaust note as of this morning, much quieter than usual. I'm waiting to hear from Tony in regards to options.