I am thinking that the DV is playing a hidden hand in this taper drama. It was my gut feeling from the outset in this particular case. I am not saying that it is the only cause of the OP's issue. I just think that it is likely contributing to the problem.

First step is I'd like to see the DV valve crushed. I'd like to see how that one change on the intake charge pressure side impacts the tapering. Once that is done then I'd like to reset preload on the actuator. But, lets set preload the old fashioned way by removing the MBC and running the actuator straight off the compressor discharge nipple. We'll probably need to cut a couple threads off the actuator rod before we are done tinkering though.

 

First, we can just use my FORGE DV for testing. No need to go start crushing stuff. Kevin has done a couple boost leak tests. I believe to about 25-30psi (I may be wrong), and if the DV was the issue, it would have leaked then IMO. But you never know.

Also, the WGA is preloaded enough. We can run it straight off the turbo and get a log, but I doubt that will help at all. Also the fact that when this happens, we do NOT hear the dump at all, basically says that the WG is staying closed when this happens.

 

You would think that for boost to taper all the way down to 8# the flapper valve would have to be wide open, right? But contrast that given with the nature of the FP 18# actuator.

The 18# actuator at worst, even with zero preload won't go to full open much earlier than 13-14# of boost. At least mine was like that. So an average one will probably allow the flapper to crack and start to lift at 10-11 PSI. So the flapper should be staying rock solid down onto the seat until eleven PSI at least.

But, in this case do we have to assume that it is full open at 8#? Wierd, huh? By definition (almost) for boost to drop(taper) down to 8#... the flapper valve has to be open and effectively bypassing exhaust gases. How is this possible at only 8# if the actuator should easily be pulling the flapper down onto the seat at that low of a pressure level?

 

That eactly what I think. For that big of a boost drop, either the WG is opening up (but its not), theres a giant boost leak or the turbo is broken somehow (maybe cracked hotside or something).

And agreed about the FP 18 WGA doing about 13-14 with no preloading at all. And I preloaded it about 3 full turns and it was pretty hard to pull onto the stud.

Yeah, it is a weird issue. Next time kevin comes by the shop, we'll test my DV on his car. If its not that, it seems like this is an issue thats take some hunting/testing, either by Kevin or by me (if Kevin want to pay my shop to do the work).

 

I am not arguing with you and I can appreciate that you are helping the OP with this issue. It is just my opinion that there is no stock IX DV in existence that uncrushed will not be full open by 25 PSI. I had one personally that lifted at 11 PSI. They are notoriously wimpy. So, it is a good idea that you try your Forge DV on the OP's car.

I just wanted him to set preload on the actuator with the WGA connected straight off the comp housing. If nothing else, this points to any quirky issues with the WGA itself such as inherent spikes and actuator rod being too long. Also, setting preload in this fashion removes the MBC from the picture which is a good thing to do in these cases usually.

Obviously I don't have all the answers to this. You are the tuner and you are the one on the scene who is dealing with the issues first hand not merely in a virtual sense like I am doing. So, your take is the more relevant one. I am just throwing a few ideas out there. I didn't mean to step on your toes at all Jay. I respect your tuning abilities and point of view and fully appreciate what you are doing.

These things involve a lot of guesswork but there is a very basic checklist that should be followed and hopefully through the process of elimination we will eventually solve this puppy.

If at any time my posts become a distraction to this thread or prove counterproductive to your troubleshooting of the issue.... Just shoot me a PM and I'll button up. Good luck!

EDIT: It is just that this particular case of taper is a real head scratcher. I mean, wow, that sudden precipitous plunge in boost pressure. Really weird, huh?

 

Yeah, next time Kevin is at my shop, we'll test with my DV and we'll also run the WGA straight from the turbo. Maybe it will give us some info or ideas.

No problem, I didnt think you were steeping on my toes. I understand you are just trying to help. Thanks. I also respect the help you put into the community. I always see you posting on lil issues like that, helping people. Respectable.

Also,I welcome your input and ideas.

Yeah, really really weird. Never seen a turbo taper this bad, even on the stock WGA with a boost leak.

 

If the OP's original stock WGA is still serviceable you could swap it back on just for comparison's sake. If the backup nut or the turnbuckle are rusted onto the actuator rod's threads then hit it with parts blaster/WD-40.

Chad's BBK turbo is supposed to work best with the stock actuator. Or you could try any other known working WGA on the turbo just to see. I am not saying that it is an actuator problem for sure. However, it is not beyond realm of possibility to suppose that the actuator could be defective.

Also, the DV: It is easy enough to do a simple test of how the thing is affecting the boost control loop. Either pull it and block off the holes in the UICP and the intake tube, or flop the valve around backwards.

I have never seen the FP 25 PSI actuator side by side next to the the FP 18 PSI unit. Is it possible that if they are visually identical that the OP's BBK is fitted with a 25 PSI actuator by mistake?

 

Sparky when you say stock 9 valves are open by 25psi are you saying with 25psi to the bottom of the valve only? With 25psi going into the top port and to the bottom I would seriously doubt it is open. I will boost leak test mine now to see if open at that boost. Now any Nov will open way early if there is no boost going to the top poet. The only negative I see with a 9 valve is that it is not big enough for a huge turbo application. I have run 35psi on a stock jdm EVO 8 MR Bov with no issues for years.

 

There is a lot of variance from one unit to the next with these things. Personally, I had one that cracked and started to lift at 11 PSI. I really don't know at what pressure it went full-open.

How do I know this? If you try it with a bicycle pump on your bench it may not open at 11#. But, this doesn't mean that installed on your car it isn't cracking early and starting to lift at between 11-15 PSI.

Try flipping it around backwards and installing it that way. Go WOT. Then compare transient response and turbo spool rate with it installed normal as opposed to backwards. Then you'll see what I mean in a practical, seat of the pants way.

Try an experiment by installing your DV backwards Batster, this will give you an idea of just how much your stock DV has been lifting. once you tried it backwards you'll want to crush it. As the song says: "You like it now, but you'll learn to love it later."

I am a firm believer in crushing the metal DV. It is not so much a difference in peak boost performance, but you gain a ton of midrange torque and power and spool up improves astonishingly. It will ultimately go full open at the same boost level. But, I guarantee it will crack later and lift at a much slower rate. Just my .02

 

Kevin actually solved this issue. He did a 4th boost test. The system held pressure again, even using soapy water reveled nothing. Then Kevin said he started squeezing couplers one by one. When he squeezed the coupler on the IC exit, it reveled a tear and it leaked. He fixed the issue and retested and it all seems good now. We will finely tune his beast as soon as he gets sometime off work.

 

I am glad that the OP is resourceful and it is especially great to hear that he solved this problem all by himself. Khuuul.

 

I am more or less a pragmatic, empirical Neandrethal. I don't place much faith in boost leak tests per se. I just am not into relying solely on checking wastegate and DV lift and functionality via boost leak tests with a bicycle pump. Sure they have their place, and can be useful in detecting TB seal leaks and etc. But, in general they are just not my style. FWIW, I can get a turbo to spool up pretty quick without resorting to this widely accepted, Mr. Science approach.

As a case in point, let's review the boost taper, or better, boost plunge scenario reported in this very thread. In his opening post(see post no.1) the OP clearly states that he conducted multiple boost leak tests. Well, a lot of good those "tests" did him.

It turns out that he did, in fact, have a boost leak. But, this boost leak had not been detected by his initial boost leak testing. Instead, Kevin had to resort to the low-tech soapy water bubble test. This is like dabbing spit on your tire stem to see if it has a slow leak. This is precisely one of the reasons why I don't put much faith in these new fangled panaceas and "tests". The soapy bubble test gets my vote over the more clinically acceptable and widely acclaimed, "boost leak test".

 

Actually, Kevin used soapy water in all his BLTs. What really found the leak, was squeezing the couplers.

 

I do the spit on the tire stem to see if the valve is leaking, Jay! LOL. Seriously though, the great thing is that Kevin resorted to his own ingenuity and resourcefulness and you steered him in the right direction. Kudos to both of you. I probably would have taken a match to thing out of sheer frustration.👍

 

Well first test run worked, the others not at all, I apparently didn't fix the issue. I've swapped out couplers also and no different, swapped out with a crushed bov (not sure who crushed it) same thing. The boost is still tapering to 6 psi.