Sticking wastegate?

[Emeraldage]

Hey all, so I'm noticing this now after taking my car back to ohio to show it to friends doing a lot of pulls... After I got the lex and 550s done.

Basically, 2nd gear around 3000rpm. Stomp on it, it pulls like crazy spins tires, hits up to 15 psi or so, slowly drops back down, when I keep ulling shifting gears it holds pretty steady ~10 psi.. I'm thinking somehow t he wastegate is taking a bit longer to open up? But shit I want to run that car around 15 full time lol. But ~14 is getting close to blowing up the turbo isn't it? Engine is fully rebuilt head stud, dpp exhaust all that fresh head. It can handle 15 just don't know about the turbo!

If it is sticking is there any way to fix or mess with it without removing it from the car? This is making me want to get a hallman boost controller but I'm scared if I set it for around 14 when it'd open the waste gate would take too long to open and it would go over 15!

 

[IndigoMKII]

The turbine design of the ct26 can't sustain higher PSI at higher RPMs.

 

[hvyman]

Stock turbo will not blow up at 15 psi. It just starts blowing hot air.

You more likely have a weak wastegate that is staying open or your exhaust housing around the wastegate flapper is cracked. a stuck closed wastegate or sticking wastegate would result in a over boost situation which you would hit fuel cut.

 

[Emeraldage]

I don't understand, if it was leaking I would be at a lower pressure right? I have dpp with 3" to a cutout so 9-10 is about where I should be. But the first gear I gun it in, it'll spike to 15 or so, and slowly go back and hold around 10 for the next gears. If I was leaking or it was stuck open I wouldn't be boosting these higher numbers right? But if it's having a hard time opening as quick as it should to bleed off pressure it causes that temporary overboost until it opens as it should?

That's exactly what I"m having, I'm overboosting for a few seconds until it goes back to normal (When the gate finally opens). Which is awesome cause that pull at 15 pounds is craazyyy. Looking around most people say the most you'll get out of a ct26 is 14 psi or so. But there is definitely more power and I might try a MBC or shimming since I have support mods. Just worried about the wastegate holding more pressure than it should and it spiking up to 16+ or something. Bu tI don't know what that turbo can do.

Also there is no fuel cut so that's another reason I doubt I'm leaking anything.

 

[Dave46]

I'm no expert but I had a similar problem. I was getting a massive boost spike and then would stay at a certain lower boost level, sometimes at 5 PSI , and sometimes at 10. I'm on stock injectors and stock afm, so my boost cut happens around 13psi... But I had a cracked coupler on the 3000 pipe, and the previous owner missed a few bolts on the turbo to the header which was causing an exhaust leak.
There's no fuel cut because your supporting mods raise the fuel cut to somewhere near 20psi.

Check your piping, check your vacuum lines. It sounds like a pretty big boost leak to me.
MBCs aren't very reliable, if you're sticking with the ct-26 it might be wise to invest in an EBC to really try to minimize the amount of hot air you will eventually be blowing into the motor.

 

[Emeraldage]

If there was a massive boost leak I would get boost cut or something a like correct? A mk3 supra with 3" dpp open exhaust and a fresh running engine SHOULD be somewhere around 10 psi right? So I don't think it would be a boost leak if it holds around 10 after the spike because that seems pretty normal. I guess I never checked to see if the turbo was shimmed but I don't remember anything abnormal. (I just took the turbo from the parts car and put it on the new engine didn't touch it, I remember the waste gate being physically extremely hard to open by hand but I have no experience with turbos so I wouldn't know.) Either way I was mostly just curious because it doesn't seem to be a serious problem. Car runs great other than pretty rich low (obviously cause 550 mod). 9-11 psi seems normal to me and around the same pressure people of similar setups get. But jesus that boost spike is crazy, there's a massive amount of power when you run it in 2nd when it spikes up to 15 or so. Pretty excited to make it run like that all the time after piggy back tune and maybe 57 trim rebuild. Then I have to worry about my w58 exploding!

Awhile ago I did make myself a boost leak tester was pretty nifty. it's where I found my original leak in the intercooler was cracked open pretty big (The car it came from was in a minor wreck). After that I couldn't find any leaks of hear anything. But my air pump could only get like 1-2psi through the system so 10+ would be a different story for sure.

Sorry for wall of text.

 

[hvyman]

If you tried to open the waste gate flapper with the actuator bolted on its going to be hard to open. Too see if it's sticking you would have to unclip the actuator and then check the movement of the flapper.

A bad actuator would seem more likely than a sticking flapper. The flapper wouldn't spike fast and then drop fast if it was sticking.

Can check the actuator with controlled air pressure and see when it opens.

 

[Dave46]

Forgive me if I'm wrong but wouldn't your boost cut be increased to a higher PSI? Your example of a well running 7mgte is correct, but you also have the 550's and bigger air flow meter housing. Capability of more fuel flow would allow for higher boost, the ecu recognizes this and adjusts the boost cut accordingly.
At least that's my understanding of how it works.

In that case you wouldn't be hitting any sort of boost cut. In my case, I did not have any fuel mods, so I never saw passed 13-14psi due to fluctuating weather and variation in spike. If I had the fuel mods, I would be seeing the same high spike as you are.

It is very possible that you have a bad actuator, this would be unfortunate but maybe put your boost leak tester to work and see if you can diagnose any issues.

Best of luck!

 

[jony89]

So I'm having a similar issue. I feel that my waste gate is actually staying open. Reason why is because wen I start the car and let it warm up I give it some gas and it always pulls hard the first time. After the first pull the car tends to have sooo much boost lag. I've done this with the car cold and hot because I know the wastegate port has small cracks so I wanted to see if different temps would make a difference (cracks expand when hot) I also took the line from my Mbc to the waste gate and used a pump to put pressure on the wg. It opened and when I disconnected the pump is snapped shut. Is there anything else I'm missing? I've checked all my intercooler clamps everything is tight. So no leak there.

 

[Emeraldage]

Hope I can just do the 57 trim ct26 sometime and this problem won't exist anymore! I'd be scared to do a boost controller on my car as it is because the boost spike might be too high and could damage the turbo.