Boost Cut? Boost Leak?

[Amontgomery]

When I rev my car above 4-5k rpm it loses power for about half a second, then gains it again quickly, then loses it again and does this in rapid sucession. My wastegate is unshimmed and I am not running an aftermarket boost controller so my boost should be around 7-8psi as I am running a full 3" turbo back exhaust with a divorced down pipe. But yet it is pegging out the gauge at around 10+ psi and pulling hard all the way up until it gets to what feels like boost cut. I tested the wastegate actuator and it moves the wastegate fine (with the line hooked to a pump it moved the wastegate at around 8-9psi) I am thinking it has a boost leak as well but the boost guage is attached to the manifold and it wouldn't show the pressures as high as they are if the piping was leaking.

I have an aluminum hardpipe kit on the way as I figured if it has a boost leak I might as well go through the trouble of fitting aftermarket piping while I am checking the entire system for leaks.

I recently change the turbo to a rebuilt stock ct26. The head has a mild port and polish job but without oversized valves attached to the block with ARP fasteners and a thick HKS headgasket. As I mentioned before, the exhaust is a full 3" turbo back with a divorced down pipe. It has not had any tuning to the engine management or fuel delivery. It has had the EGR and all emissions control devices removed.

 

[Facime]

It has had the EGR and all emissions control devices removed.

?
When you say "all emission control devices" what specifically are you referring to and why was it removed?


It sounds like your wastegate isnt opening properly. Check to make sure the vacuum line from the turbo outlet to the actualtor is in good shape. Its possible the actuator itself is bad (pretty rare though). Was the actuator replaced with the turbo or did you reuse one you had? Have a spare?

 

[Amontgomery]

The actuator was reused from the stock turbo but it seems to be working properly (It opened the wastegate when I applied about 8-9psi with a pump). The line is brand new, though about an inch longer than stock.

I didn't do the work before the turbo swap. I assume it has had the charcoal canister removed and the EGR blocked off. The PCV needs new hoses because the current ones smoke after the engine is warm. I didn't think that it could be connected to the wastegate operation though.

 

[thebuddrik]

With my old car I had the same mods and probs. My arm from actuator to the actual wastgate was slightly dammaged. I changed it and the prob went away.

 

[Amontgomery]

OoO!! I hope thats not it on my car. I don't want to have to pull that turbo again until I put a bigger one on. But it would make it a lot easier to put in the hardpipe.

Its weird though. It seems to open fine when I use a pump to apply pressure to the hose.

 

[thebuddrik]

I didnt remove the turbo to swap it out. I had tried everything else and nothing worked. Thats when it hit me, when they were shipping me my jdm some how the pallet broke and it smashed the oil pan. I was reading the TSRM it says not to grab the turbo by the accuator rod, so I put 2 and 2 together and I removed the E clips and swaped them out. Just becarefull, those little E clips like to fly whenever you pull them off.
At first I was flattered that I was making so much BOOST!
Good luck

 

[mk3 for life!]

does it throw a cel when it cuts in and out? mine did the same thing before i changed my knock sensor wires, then it went away, it also cuts in and out when your tps isnt adjusted properly, i had that problem too

 

[Amontgomery]

To tell the truth I don't know about the CEL as I am to busy either looking at the boost gauge, wondering why it is pegged out, or looking at how fast the car is going with over 13psi boost. The knock sensor wires have already been replaced though. I don't know how to check the TPS on a MKIII any pointers without adjusting then driving and repeating until I get it right?

 

[thebuddrik]

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=23

check for codes

 

[mk3 for life!]

when i did mine i had it throwing code 51(tps sensor) and as told by IwantMKIII that code is a real time code which means it goes away as soon as the problem is fixed so i loosened the tps and turned it slowly till the code went away then said f-it and left it alone. THIS IS NOT THE CORRECT WAY!! but i wasnt going to worry about it because it was running perfect.

^ that link he gave you does explain the correct way somewhere on that website

 

[thebuddrik]

I did the same thing and it worked... untill I found out that if I bring the RPMs up to about 1300 it starts to rev up to 2k then down to idle over and over. I am actully in the process of having my head rebuilt to fix a burnt valve and today I am gona recalabrate my TPS so when I am finished the problem will hopefully go away.

 

[Amontgomery]

I am not throwing any codes. I did see something that looked suspicious but it doesn't make sense. A ground wire from the head to somewhere was loose at the other end. Other than that everything is fine.

What is really getting me about this whole thing is a wastegate actuator is a mechanical device that operates off of pressure through a hose. It opens fine with pressure applied from a hand pump but not from the pressure from boost, which is reaching the intake manifold because it is registering on the boost guage. So the turbo is making boost and there are no leaks because it is showing on the boost gauge. The pressure is getting to the wastegate actuator as all lines to it are clear.

This is seriously frying my brain.

 

[thebuddrik]

That sounds like what I was talking about in post #4. Has your turbo ever been out of the car? Is there any chance that that linkage could have gotten bent? You probablly couldnt even see the differance if it was.

 

[thebuddrik]

I just skimmed over the post in your sig and I bet that it is your linkage.

 

[Amontgomery]

I have a second turbo that I swapped off of the car when I put the new one on. Could the linkage on that one be swapped onto the new one? Both are CT26 just one has 11 blades and the other has the blades in pairs.

 

[thebuddrik]

not sure but it couldnt hurt to try. that was why i did it on my old car. after that i would floor it an just smile.:biglaugh:

 

[Facime]

worst case swap out the actuator and bar together. That might be easier due to difficulty getting access to it under the turbo.

 

[Amontgomery]

Ok. This is really weird. I just got back from a drive and everything is 100% back to the way it should be. I don't know what I did to fix it, maybe the wastegate actuator was just locked up and all of my pumping freed up what was locked up. I went through 3 gears at WOT and it never got to 8psi on the guage. It would stammer when it shifted to the next gear but that is just due to the fact that the revs dropped to 3500-4000rpm.

I even pushed on the throttle linkage with the hood open and watched the linkage to the wastegate. Moved just like it should.

Thats just too weird for me.

 

[Facime]

It could have been bound up. Does it look all coroded and nasty? My guess however is that you had a bad seal on the pressure signal line and pulling it and inspecting it and replacing it got a seal. If it was a sticky actuator its likely to do it again.

 

[Amontgomery]

Can just seals be had for a wastegate actuator? or do I need to buy a whole new actuator?