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Discussion Starter #1
Hi all,

this is a long read but please bear with me!

I am having some issues with the sequential system, more precisely I think it is the pressure tank or some of the lines from/to it, since everything else seems to work fine. In low rmp and especially in first gear I was having no second turbo. So today did some testing with TTC.

I bought two one-way check valves (tested and working fine) and placed them before the IAC and EGC valves. VSV's for these valves are completely ignored, I have connected the valves directly to the output of the pressure tank. Very carefully triple-checked the directions of the check valves and they are correct. The idea is once the car boosts, it should open the valves and keep them that way, even if my pressure tank is not working correctly.

BUT by some reason this is not working as it should. The first time I drive the car and boost it (the gear does not matter) it work flawlessly - I have both turbos come online as they should and my first gear missing second turbo issue is not there anymore. I was really happy and of course stepped on it again and there is no boost at all. Absolutely no boost, the car just goes as an N/A and the boost gauge reads nothing. The sound of the turbos is also not audible, it is like they are not mounted on the car at all.
Stopped the car and started removing and checking all the hoses I changed and fiddled with. Strangely everything seems perfectly fine, when I remove the check valve from the IACV and EGCV the pressure escapes from the valves as it should. Messing with all this decided to try again and by mistake mounted only the EGCV check valve and forgot the IACV connected directly to the ouput of the pressure tank.
Drove the car and the result is that I have both turbos every time on every gear, but before 4000 rpm the car sounds a bit strange and at around 4200 the car suddenly builds boost and just goes as it should. But it is very sudden, there is no slow spool as it should with the TTC.
Probably this is because the IACV is connected directly to the pressure tank output which is malfunctioning, but I just can not think of a reason why there is no boost using the check valve for the IACV? From my point of view using this check valve method, I am doing something like a "permanent TTC", because even with the car off the IAC and EGC valves are open, just because the pressure will be held there by the check valves.

I know this is a long read, but I am kind of irritated now, because I can't think of any logical explanation to this issue.
Any help will be greatly appreciated!!
 

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Discussion Starter #2
Here are two pictures of the install, in case someone sees something wrong. I try to securely clamp down everything, so I guess it won't be an issue of that type.
 

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Stock Twins King
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Are you sure you did it correctly? Also, are you sure your pressure tank is OK and has no leaks. If the pressure tank cannot hold or has a leak somewhere it will loose all its pressure quickly and not have enough to keep the to valves open. But if you can let the car sit for 10 minutes then release a hose and hear the escape of pressurized air then it might be good.
Doing the TTC check valve method is clean and simple. It is a 10 minute hook up if you do it right. You need the check valve facing in the right direction. One to the IACV actuator input and one to the EGCV input. Pressure goes to them and keeps the actuators open all the time.

If you want a picture I know I have them on my site www.97supraturbo.com

Stu
 

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Discussion Starter #4
Hi Stu, I am pretty sure I did it right, and I used check valves exactly because I think my pressure tank is not okay. So using check valves in theory I do not need the pressure tank to hold the pressure, the check valves will do this for me. And they do - when I shut off the engine and remove the check valves I can hear the air escaping, so it is there. Also the check valves have arrows on them, so it is pretty hard to hook them in the wrong direction. I have posted pictures of the install.
 

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Discussion Starter #6
The first time the car boosts is perfectly fine, so I assume all valves open correctly, but after that does not matter what I try there is no boost. There even is no delay, just the boost isn't coming even at 6k RMP. Shouldn't the check valves keep the pressure between them and the IAC and EGC actuators, so they remain opened, even when I am of boost? And the next time the car boosts the valves should be still opened and I should get boost? Still can't get my head around the fact that it works the first time and from then on there is no boost.

So in case since I think my pressure tank is not working as it should, my only solution is to permanently wire the valves open? I thought the check valves method works even with not so good working sequential system, but probably I was wrong.
 

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Discussion Starter #8
Okay, I few strange things happened today.

First, I got tired of trying to make it work with the check valves and connected the IACV and EGCV actuators directly to the pressure tank output. And boom, the car is in TTC mode. Strangely, the pressure tank seems to work fine at this point. What is even more strange is that the car before was connected just like stock, with all VSV's and actuators connected like from the factory, in another words in sequential mode, BUT worked in TTC mode. But I had an issue that the second turbo did not come online in first gear. Now it works fine.
Simply putting check valves between the actuators and the pressure tank as a result the car stops making boost. I tested them multiple times off the car and they work fine. But when I put them on the car for some reason the whole turbo system stops working.

I am not sure how and why it was working in TTC mode when everything was wired as in sequential mode. Maybe the previous owner made some other mod for the TTC mode? Also maybe this has something to do with the issue when I put the check valves. I checked the VSV's and they are not fiddled with, when supplied with 12V they click fine.

Also probably completely unrelated my check engine light started working, I have never seen it working before. Even when I resoldered the circuit board, there was just no signal coming to the bulb from the ECU and now out of nothing it started working.

This car continues to amaze me, today two completely separated things basically fixed themselves and started working and I can't explain any of it.
Hell, if I want to go back to sequential I will not be able to do it, because even with sequential wiring the car works as TTC.
 

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Stock Twins King
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Few things to check as you seem to be new to this car. Make sure that the EGCV ceramic flapper arm is not tac welded to the iron frame. Maybe the internal ceramic flapper has been removed.
Look around your ECU area and make sure no one installed an ETTC switch. This might cause some of the electrical gremlins. NO WAY will your system work in Seq if either of the VSVs/Actuators are not up to OEM. Maybe you have a torn or ripped hose down near the firewall where the EBV actuator is and where all the PT lines run along the firewall.

 

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Discussion Starter #10
Thanks again for the help Stu! This diagram is a life saver.
The ETTC is something I really have not looked for and maybe there lies the answer. I hope so. If there is no switch, I will look the EGCV flapper when I have more spare time to disassemble everything.
And yes are right, I am relatively new to the car, only got it a few months ago, but even will the occasional issue I am loving it. Still trying to learn how everything works, but I am slowly getting there.
 
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