Boost creep out of the blue

[TURFNNSURF]

Sorry this is going to be a little long, but I feel that to get the best answer I must supply the most info.

For the last few months I have been running my PTE GT3255, internally gated, at 18psi with my MBC. NO BOOST CREEP on any of my WOT pulls or at the track during test and tune night. Tues of this week I took the car to Turbotrix for some dyno time to see what 21 psi could do on my Auto. Monday I took the high flow cat off and put in the test pipe to get better wideband O2 readings on the dyno. My first pull on the dyno @ 18psi with a 94 pump gas rich street tune yielded a poor 270awhp and 230tq. NO CREEP!!
after upping the boost to 21(my 1g BOV won't hold much past this, Greddy type-S is waiting for install) Anyway after tuning for 21psi on pump gas still (no creep yet) the car managed 305awhp and 270tq. I know this turbo likes big boost but that will have to wait till next spring and the Mitsubishi shootout at Englishtown.

Fast forward to Thurs morning, I get in the car warm it up and start off for the highway to work. When I see my chance to merge with traffic I jump on the gas, 21psi comes in by about 3800rpm, then I see the boost start climbing toward 25psi as 6000rpm approaches. WTF, it didn't do that on the dyno???? I pulled over at the next exit and turned down the MBC to about 15psi got back on the highway and the same thing, hit 15 psi by 3500 then it just kept going toward 20+ by 6000rpm. As of this afternoon I have bypassed the MBC and run a vac line from the compressor housing straight to the wastegate and it still overboosts.

Could my wastegate actuator have crapped out on me overnight?? I have to put my high flow cat back in to pass inspection in a few months anyway, maybe putting it back on tomorrow might help but IM not sure. IM looking for any other suggestions or ideas I may have missed..

Thanks in advance fellow Tuners.

 

[DSM90AWD]

Could you have accidentially bent the actuator rod and/or is it binding?
Out of curiosity does your PTE Exh housing have the divider removed?

 

[TURFNNSURF]

Good questions John.

The Exhaust housing it cut I bought it like that from DSMotorsports. Up until yesterday I had no creep issues at all. The only changes I made to the exhaust were to remover the 3" high flow cat for a test pipe.

Thinking back to Tuesday afternoon after my dyno run. I did make a slight change to my actuator arm. The reason behind this was that it seemed that the turbo would get to 10psi instantly then from 11 to 21psi it would build slower, but hold solid at 21psi. My thought was that the wastegate was blowing open a little after 10psi causing the turbo to work harder to make it from 11 to 21psi. I adjusted the actuator arm a turn or two tighter to help hold the flapper closed. Maybe that was a bad idea, in hindsight.


After reviewing my datalogs from the dyno runs I had noticed some knock that needed to be tuned out from 3800rpm up. This corresponded to that 10psi theory of the wastegate opening early.

I'll adjust the actuator arm tomorrow, back to the original setting and take a test drive..

Thanks John for making me remember that little adjustment.

 

[DSM90AWD]

Glad to have helped. Now get that beast tuned and running some big HP

 

[TURFNNSURF]

Update, as of this afternoon I adjusted the wastegate actuator arm to the original setting. I have it set to just keep the wastegate flapper closed with no pre-load at all. I took the car for a run and the boost still climbs to 20+psi. This is really bugging me, I guess the high flow cat goes back on tomorrow.

 

[oldman]

The reason behind this was that it seemed that the turbo would get to 10psi instantly then from 11 to 21psi it would build slower, but hold solid at 21psi.

That sounds a little like creeping as well, maybe it was creeping on the dyno just ran out of rpm. Put the cat on and see what happens.

 

[TURFNNSURF]

Oldman, I see what you mean, but I had 4 pulls in a row at 21 psi when the MBC was set to 21psi and it held solid there from 3800 to 7000rpm. The creep only happend after i left the dyno. The following day is when I adjusted the actuator arm and the creep started shortly after that. Im starting to wonder if the pre-load I put on the actuator caused a problem internally and now the diaphram doesnt respond to boost pressure to push the wastegate arm open.

 

[lowridin2g]

a leak at the wastegate could most definetly cause boost creep. even a small crack in the wastegate will cause that. check to make sure that theres no cracks in the gate and the hose form the mbc to the gate. look it over really good

 

[TURFNNSURF]

Latest update on the creep problem. I put my high flow cat back, in place of the test pipe, and the creep is gone... I guess that my 3" exhaust flows plenty for my GT32 turbo. When I had my B16g on the same exhaust setup it didn't creep with the test pipe, maybe it just couldn't flow as much as the Garrett does.

In all honesty I like the exhaust tone better with the cat on, plus I have to have it for inspection in a couple of months. It may rob my car of some HP, but at a solid 21psi again, the car feels awesome.

I know an external wastegate would solve my creep problem in the future. I just don't see it as practical for a daily driven car unless I can route the dumped exhaust back into the downpipe. Are there setups for external wastegates to dump back into the downpipe?

 

[DSM90AWD]

That's cool you were able to find the issue.

Plumbing an external WG dump back into the exhaust would be pretty easy to do. Just mark your DP where you'd want it to plumb back in and take it to a exhaust / machine shop to have them weld a short 1.5" OD piece of tubing. Then connect the dump to this DP piece with some flexible SS tubing you can find at JCW or NAPA.

Of could just get a custom O2 housing with dump re-route from 122performance.com or VictoryPerformance.com.