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Boost cut/drop issue

Old Oct 19, 2018, 05:08 PM
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Boost cut/drop issue

Hey everyone. I have been fighting an odd boost cut/drop issue for the past week or two and cant seem to figure it out. Need some guidance from people who know more about Evos then me (not hard to do). So here is the breakdown of how things came to be. Car is pretty much a stock 57k mile 06 MR.

- Bought Evo and enjoyed it stock for a few weeks. No issues. Then decided it was time for tuning and more boost.
- First step was to add a 3 port solenoid so I could up the boost. Install went fine as it is pretty straight forward.
- While the intake box was out and since I was already half way there, I did a boost leak check. It passed just fine.
- After it was installed, I changed everything I needed to in the tune and took it for a spin. After multiple runs, changing every setting I could, I could not get the solenoid to control boost. There were 2 times for 1/4 second I hit 30 psi.
- After multiple nights of being fed up with failing, I put the stock solenoid, lines and tune back on.
- Now that everything was back to stock, I was seeing 22-23 psi tapering down to about 19 psi. Previously with the same setup, I was at 18 psi tapering down to about 14 psi. At this point I did not do full 7500 rpm pulls.
- It was hitting the boost I wanted so that made me happy. But then once tuning began, I ran into issues.
- I was getting a very bad boost cut and will not make more then 7 psi above 5500 rpm.
- I initially thought the ecu was cutting boost. To get around that, I installed a manual boost controller and bypassed the stock solenoid. Same results. See below for a 1-3 gear pull.



As you can see, its dropping off fast. The odd thing is that if I am on the highway, I can load it up for almost as long as I want in 5th and 6th gear and it wont drop boost at all. Seems to happen around 5500-6000 rpm for the most part. From the time I did the first boost leak check, I only pulled off one hose. I double checked that hose, tightened all the clamps, gave everything a look over and found nothing. To go even further, I pressurized the wastegate and it starts to open right at 14 psi. It holds pressure and does not leak. I also sent some pressure and vacuum to the DV and it does not leak either. This is where I am currently at.

So..... what else could it be? Can the DV be opening up on me? Can the wastegate be opening up on me? Did the 30 psi spike cause a hose to blow? When it drops boost, I can clearly hear it. It sounds like a wastegate being opened and bypassing, like a huge rush of air. I can post a video if it will help.

I know most of you are going to say its a boost leak but why will it hold 20 psi in the taller gears/lower rpm? I would assume if it was a boost leak, it would never be able to hold boost. Where to go from here?
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Old Oct 19, 2018, 09:47 PM
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Tonight I ran 2 more test. First one, run WG spring pressure only (14 psi). Same result. Drops boost. 2nd test. Pop out DV valve, pressurize to 20 psi and see if I can move the piston. Nope. Wont budge. Not that. Guess at this point the next step is to do another boost leak test to see if anything really did blow. And if I have to pop the air box out again, an aftermarket one is going back in its place.
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Old Oct 20, 2018, 09:11 AM
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Definitely sounds wastegate related to me.

It may open at the correct pressure, but can it hold against the exhaust flow? You may just be blowing it open, Normally I'd say it's ecu control issue, but if you put a manual control on it, that solves that issue.

Make sure no leaks at above your desired boost pressure.

I'd swap wastegates.
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Old Oct 20, 2018, 04:39 PM
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Thanks for the input. I have a Turbosmart wastegate on order that I will pick up from them on Monday. That would be nice if it solves my issue. I went with their 18# version. Does not look like it's going to be fun to install.

I figure if I have to install the WG, it would be a whole lot easier to remove the radiator. And I am fine with that since I doubt the coolant has ever been changed. I'm going to order up a CAI on monday and throw that on while I am down there as well. Might as well do an o2 housing and down pipe right? Haha
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Old Oct 22, 2018, 01:32 PM
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Will this solve the issue? We will find out whenever I find time to install it!

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Old Oct 22, 2018, 10:13 PM
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Figured I would get it installed sooner then later. Wasnt fun but I'm getting pretty good at taking apart this portion of the car! Only broke 1 super rusty bolt for the heat shield. It can live without it.

Now to my prediction. I'm going to have a lot of boost. More then I want. I pressure tested the new wastegate and yes it starts to open at 18 as it should but by 25, it only opens a 1/4". The old WG starts to open at 14 and by 20 it's a 1/2" open. I get that it's got more spring pressure and it takes more to open but it just doesnt seem like it's going to open enough to bleed off the needed exhaust. We shall see tomorrow morning!



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Old Oct 22, 2018, 11:37 PM
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Couldn't wait until the morning. Took it around the block. My prediction was wrong. Hits 18 psi as it should. Didn't see if it holds through the entire rpm range though. That will be tomorrow.
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Old Oct 23, 2018, 11:12 AM
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And its still dropping boost off. Seems to hold it longer but still drops off. Ill do a log on lunch and post the results. I will also try to do a log on the way home showing how it holds boost no problem in the taller gears.
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Old Oct 23, 2018, 01:20 PM
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Is it still on the manual controller?

Just run a hose from the turbo to the wastegate and bypass any boost control methods.
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Old Oct 23, 2018, 01:34 PM
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Also, what BOV are you running? It doesn't leak under pressure?
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Old Oct 23, 2018, 02:00 PM
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Still on the manual controller. Currently set to as low of boost as it can go (should just be passing through the valve). I will try bypassing it completely but not expecting any change.

Stock BOV. I pulled it completely out, pumped it up to 20 psi and tried to push the plunger in. It wouldnt budge. Not even a little. I put vacuum to it and it opens as it should. Both psi and vac held for 30 min with no drop. I also pressure checked the line that runs from the intake manifold to the BOV and had no leaks. I might pick up a Turbosmart valve just to try it out.
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Old Oct 23, 2018, 02:18 PM
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How are you doing the boost leak test? You are testing the entire system through the turbo correct?

Bypass the controllers completely, if it doesn't hold a constant 18lbs, we need to look else ware.
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Old Oct 23, 2018, 02:35 PM
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Correct. Pulled the intake tube off the turbo inlet. Put custom made thingy in place, hooked it up to regulated air compressor, fill the system to 25 psi (verified with separate gauge on a port) and squirted down all connections with soapy water. If it bubbles, its leaking. I had no bubbles. I am going to put a smoke tester on it today to see if that reveals anything new. If it doesnt, I will do another boost leak check.

Data log coming shortly!
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Old Oct 23, 2018, 03:24 PM
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If you don't hear the leak, it's not moving enough air to cause such an issue.

Boost leaks usually cause other issues in the first place, not this drop off problem. Smoke test is overkill IMO.

Could also be the turbo, any shaft play? Impeller hitting the housing would make similar spikes.
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Old Oct 23, 2018, 03:49 PM
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I checked the turbo out last night. I would say there is nothing abnormal about it. Shaft play was fine, no leaks, no hurt fins. I didnt pop off the o2 housing so I cant say anything about the exhaust side of things.

Another 1-3 gear log as of a couple minutes ago. I held 2nd gear out a bit longer so you can really see the dip and how it flattens out. Yes that is dipping down to 3 psi....

Edit - this is with no MBC. Strictly line pressure going to the WG.

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