[WhiteVR4demon]

For those who read about me finding a torn vacuum hose, we'll apparently that wasn't my problem. I installed a boost guage (Greddy 52mm E-guage-very simple BTW) and did a WOT on the torn hose=.5 bar, so I'm pretty happy about replacing the hose and doing another WOT, thinking it will read about .7 bar, but it didn't happen, it still was at .5 bar.

The 2nd turbo does hold the .5 bar to redline, but damn its not pulling for shit. Last night me and a mechanic (domestic mechanic BTW) rechecked all the hoses, but everything seems fine. Do you think my turbos are on their way out? This is really fustrating

What else do you think I should check? Anything would be beneficial to me, is there anything under the car I should check (my friend has a lift)? I have the Greddy EVC-EZ ready to install, but I want to fix this first.

Its obvious there is a boost leak, which hoses should I concentrate on? Also, I used 4mm size hose for the guage and hose from actuator to VSV, I don't know if that has any significance.

Please help me

john

 

[sleeper]

1)Eliminate the other vacuum hoses as a source of boost leak. The underside of the hood has a diagram of the vacuum hoses. Inspect each for cracks, make sure they don't easily slip off a VSV nipple or connector.

2)Check/re-tighten the intake plumbing hose clamps, starting from the Y-pipe where boost from 1st and 2nd turbo join, all the way to the throttle body. You are going to have to get underneath the car to check the clamps for the intercooler. If still no go, pressurize the IC plumbing starting from the 1st hose right after the Y-pipe and plug the end of the IC hose that connects to the throttle body.

I went through my own "boost leak" phase and it was no fun, so just keep us updated.

 

[WhiteVR4demon]

The underside of the hood has a diagram of the vacuum hoses. Inspect each for cracks, make sure they don't easily slip off a VSV nipple or connector

thanks sleeper, one more thing, with the car on and pulling off a vacuum hose, should their be suction/hissing sound coming from the pulled hose? Does the car have to hit a certain rpm or what?

thanks,
john

 

[dzeiler]

from the upcoming revision to MKIV FAQ Has not gone though the review process yet
2. how does the stts(sequential twin-turbo setup) work? sequential turbo diagram first off, the is no #2 wastegate. there is only one wastegate and it comes off #1 turbo because that turbo is always on line, therefore you always have a wastegate. there are 4 sets vsv's, actuators, and control valves for the sequential turbo system. each vsv is simply a solenoid that is either 100% open or closed, allowing manifold pressure to pressurize the different actuators that open/close the four different valves.wastegate: when the manifold reaches 11psi of boost, the ecu sends a signal to the wastegate vsv, this allows manifold pressure to build in the wastegate actuator which opens the wastegate.exhaust gas bypass valve: somewhere around 3500 rpm, the ecu sends a signal to the exhaust gas bypass valve vsv, which allows manifold pressure to build in the exhaust gas bypass valve actuator which opens the bypass valve. this is a small opening inside the #2 turbine housing which allows some exhaust gas to go through the turbine of the #2 turbo which makes it start spinning, and dumps the exhaust gas out the exhaust piping coming off of #1 turbo. since it is a small amount of exhaust gas, it pre-spools the turbo and does not get it up to full operating speeds. this will smooth out the transition from 1 to 2 turbos. this valve is similar to a wastegate in design, but is located after the turbine wheel instead of in front of the turbine wheel like a wastegate would be. this is not a wastegate!exhaust gas control valve: this valve is located in the exhaust piping downstream of the #2 turbo. when this valve is closed, all exhaust gas must go through the #1 turbine wheel to get out through the rest of the exhaust system. at around 4000 rpm, the ecu sends a signal to the exhaust gas control valve vsv, which allows manifold pressure to build in the exhaust gas control valve actuator which opens the control valve. this allows exhaust gas to go through #2 turbo and out the exhaust system which brings the #2 turbo up to full operating speed.intake air control valve: this valve is located in the intake tract coming off of #2 turbo. it is closed below 4000 rpm so that boost pressure coming off of #1 turbo cannot backup through the #2 turbo and back out the air cleaner/suction of #1 turbo. there is also a 1 way reed valve within the same housing of the intake air control valve. as the #2 turbo starts to prespin at 3500 rpm, it will build some boost. if it builds enough boost, it will open the 1 way reed valve to allow this boost into the intake tract to join with the discharge boost pressure coming off of #1 turbo. at somewhere over 4000 rpm, the ecu sends a signal to the intake air control valve vsv, which allows manifold pressure to build in the intake air control valve actuator which opens the control valve. this allows the full boost pressure coming off #2 turbo to join in with that coming from #1 turbo and you are now fully on line. usually, the exhaust gas control valve will open first, which gets the #2 turbo spinning at full rate so that it is building good boost before the intake air control valve opens, allowing this boost to join in with that coming off #1 turbo. if the intake air control valve opens before the exhaust gas control valve, the boost pressure coming off #1 turbo will go backwards through #2 turbo, spinning it backwards if there isn't sufficient exhaust energy to keep it spinning forward. when the exhaust gas control valve opens, and the #2 turbo has to reverse the direction of the spin. this is a tremendous strain on the turbo shaft and bearings. if the sequential operation is not a well orchestrated symphony of motion, it is easy to see how the #2 can be prone to failure. For an alternate explanation go to new car features, ncf 91- 95 are the appropriate pages. back to start
3. what does a vsv do?vsv is short for vacuum switching valve. it is just an electronic solenoid, which either opens or closes 100% when energized. this will allow the vsv to either pass boost pressure through it from the actuators (like the wastegate actuator) or block it off.back to start
4. How to trouble shoot the sequential system.
As you can see from the discussion in number 2 above the operation of the sequential system is complicated and requires all it s components to be functioning properly. Failure of a component will cause the disrupt the proper sequential operation of the turbos and can lead to failure of one or both of the turbochargers.
If any of these valves aren't working properly, you'll have low boost problems:

1. BOV (boost will get bled back to intake)
2. EBV (loss of exhaust energy)
3. EGCV (loss of exhaust energy)
4. WG (loss of exhaust energy)

Now if the EGCV, or EBV aren't working properly, you should have strange transition problems, as well as low boost on the low end.

If the problem is the WG, you should suffer low boost consistently, whether it's only #1 or 1+2.

One way to sort his out is to put the car into True TwinConversion(TTC) as a diagnostic tool. TTC instructions If your boost problem goes away with TTC it has to be one of the VSV or actuators that is malfunctioning. ( as an aside many list members feel that TTC is safer for your turbos because by eliminating the sequential operation eliminates the chance that the turbo will boost against a closed valve and twist the shaft).
The actuators can be checked in the car. All you need to do is hook up a pressure source (I use a 60cc veterinary syringe) and pressurize the actuator, then watch to see if it leaks down. It's pretty simple. Don't go over 20 psi with this as you'll blow an actuator diaphragm or overextend an arm.
The VSV's are the same. Hook up pressure to see if they leak. Then apply a ground to the wire going to the ECM to actuate the VSV and see if it opens. Of course they are not all normally closed, so you may need to check flow just the opposite,

If it's on the compressor side, it could be your BOV passing at low boost. These are easy to check and just need a source of vacuum. There is the suck and blow test… suck on the smaller tubing while a friend blows down the larger tubing if he can blow through with out resistance it is normal. If he cannot blow through while you are NOT sucking that is normal. operation.

Another possible source of the problem is a vacuum leak. The newest of the surpas are 3 years old as this is written (Dec. 01) The oldest is 8 years old. The various rubber control lines get brittle and leak. The leaks may not be obvious to a superficial look. I suggest replacing them with silicon vacuum hose which has the additional benefit of looking great. Short of that if you suspect that is the problem pull the individual hoses to inspect them .

 

[sleeper]

thanks sleeper, one more thing, with the car on and pulling off a vacuum hose, should their be suction/hissing sound coming from the pulled hose? Does the car have to hit a certain rpm or what?

thanks,
john

With the car on, idle or in gear, there is pressure in the vacuum lines and yes you will hear the suction/hissing sound.

 

[WhiteVR4demon]

dzeiler, thanks man, will print it out and back to my friends shop I go, we'll after work

With the car on, idle or in gear, there is pressure in the vacuum lines and yes you will hear the suction/hissing sound.

sleeper/dzeiler, when we pulled some hoses off, there was no suction/hissing sound, and it was actually on several hoses, this didn't seem right, what are you thoughts on that. And the car was on park, reving it up, but no pressure.

john

 

[Grant]

Any hose attached to the pressure tank will release pressure when you pull it off. This is GOOD, its supposed to do this.

Another part from the new FAQ:

Q: My boost is acting strangely, and I do not have a boost leak. What could be wrong?

Do you really not have a boost leak? An intake leak test is the only way to be sure.

If not, the first thing to check is the hoses. See the hose layout diagram on the underside of your hood? Make sure all the hoses listed there are connected properly. The main culprits are the smaller 1/8" hoses that attach to the intake air control valve and the exhaust gas control valve. Some are hard to get to, just remove whatever you need to check them all.

If all the hoses are in good shape, then the next thing to check is the solenoid valves (VSVs) themselves. The VSV for the intake air control valve (IACV) is located near the firewall on the left side of the motor. Its connected to a 1/8" vacuum hose which attaches to a hockey puck looking thing (the IACV actuator, http://www.mkiv.com/techarticles/ttc/ttc10.JPG). When the VSV is not powered, it should not allow air to pass through it. The side attached to the metal mesh of pipes should be blocked, and the side attached to the actuator should vent to the atmosphere.

The VSV for the exhaust gas control valve (EGCV) should perform exactly the same, but it is harder to get to. It is located directly behind the wastegate VSV, with one 1/8" hose going straight up and another going straight back.

If the VSVs check out ok, the next thing to check is the pressure tank. The 1/8" lines leading to each VSV should be pressurized at all times by the pressure tank. If these lines aren't pressurized when you remove them, its likely the pressure tank is bad.

If the pressure tank is ok, next try testing the actuators themselves. Apply air pressure to each actuator (the hokey puck looking things attached to the VSVs, 10 psi should do it) and ensure that they are not leaking and correctly actuate their respective valves. For the IACV, this can be easily seen. The EGCV is harder to see, but it can easily be heard if you have an aftermarket exhaust (the exhaust note will get deeper and louder). If the actuator arm on the EGCV breaks, the exhaust will rattle excessively (note that some rattle is normal with aftermarket exhausts) and the car will not boost well at low RPMs.

Some people perform the temporary TTC mod to troubleshoot boost problems. If the problem is the IACV VSV, EGCV VSV or the pressure tank, the temporary TTC mod will fix the problem.

Note that any malfunction of these parts is suspected to lead to sudden second turbo failure, also known as the death whine. If your car produces exactly zero boost when the second turbo is supposed to kick in, has an excessive amount of oil in the intercooler pipes, and makes a sound like this (http://www.mkiv.com/techarticles/death_whine/death_whine.wav), then you second turbo is probably blown, sorry.

For more information on the Supra's sequential turbocharger system, see pages 88 to 95 of the NCF.

 

[WhiteVR4demon]

damn, thanks Grant, where is this "new FAQ"


The turbo's work, obviously with the .5 bar reading, but why is there no pressure when I disconnect some hoses?

thanks,
john

 

[dzeiler]

damn, thanks Grant, where is this "new FAQ"


The turbo's work, obviously with the .5 bar reading, but why is there no pressure when I disconnect some hoses?

thanks,
john

we are working on it DZ