Toyota’s unique sequential turbo system found in the 1994-1998 Twin Turbo Supra can be very technical and complicated to the uninitiated. But learning how to troubleshoot 2JZGTE sequential turbos can be easy and very straightforward once you get down to it. Common issues with the 2JZGTE sequential turbos can range from turbos spooling incorrectly, very slowly or not at all. Whether you are fixing an issue or modifying your Toyota VSV system to change how the turbos work, this writeup will help you diagnose your sequential turbo problem.
When your 2JZGTE is having problems boosting on a stock sequential setup, chances are your VSV actuators are to blame. These vacuum switching units help control various items on your 2JZGTE, from sequential turbocharger control to emissions. These VSV control units are basically diaphragm plungers that opens when the right amount of pressure is applied. When one side of the VSV valve receives this pressure, the diaphragm presses against the rod which opens the valve.
Like all plunger style valves, the VSV can become clogged, contaminated or bind when fully extended. We’ll also go over how to test each vacuum unit for proper operation and check that the valve’s resistance is within specification.
Today I’ll be showing you how to troubleshoot 2JZGTE sequential turbos by locating and testing each of the 5 sequential components, and explaining where each VSV is located and how it works.
What is the 2JZGTE Sequential Turbo System?
There’s five components that are needed to properly operate and manage your sequential twin turbocharger setup on your 2JZGTE. Intake Control, Exhaust Control, Exhaust Bypass Control, and the Pressure Tank are the parts you will need to test.
Of these five components, you are interested in just 2 of the controls that control and modulate the sequential turbos on your 2JZGTE. We’ll begin with the wastegate Actuator and the VSV for the wastegate itself.
Locate the wastegate VSV under the primary intake snorkel that leads to your 2JZGTE intake system. Note that there are 2 separate VSV units here, do not confuse the exhaust bypass gas VSV for the wastegate unit.
The wastegate VSV is the first unit we’ll be testing. This vacuum switching unit is controlled by your 2JZ ECU and directly controls the internal wastegates on your 2JZGTE to keep the boost at stock OEM levels (10psi). Remove the wastegate VSV to test the resistance between the two terminals on your wastegate VSV valve.
When measured cold or at 20°C (68°F) the resistance value should be within 22 – 26 Ω using your multimeter of choice. If the resistance shows good between these two terminals, next apply power to the two terminals as shown below.
The next VSV valve we’ll be testing is the Exhaust Gas Bypass Valve (EBV) which is next to the wastegate VSV near the intake side of the engine. This VSV is responsible for spooling the #2 turbo in preparation of turbo transition. When this VSV opens it allows pressure to bleed off into the second turbo, and getting it up to speed until the actuator is fully opened allowing for a smooth engagement of the bigger turbo.
Depending on the year make and model of your engine, this valve may or may not matter. For most OBDII 2JZGTE’s found stateside, this EBV seems to be bypassed which is a modification that pre-1995 Supra owners most commonly do first. JDM Aristo engines that carry a slightly different VSV for the actuation of the second turbo, but the testing procedure remains the same.
The next VSV we’ll be looking at is the Intake Air Control Valve (IACV) which is mounted to the top of the crossover pipe between your turbos. This VSV has two ports one that leads to the actuator arm shown above. This valve is responsible for bleeding off excess boost pressures above the 10psi mark. If your 2JZGTE does not boost over 10psi for whatever reason, check your IACV valve first, as a malfunctioning part will result in limited boost.
For more on how to test your Toyota 2JZ VSV valves, check our How-to article here. If your IACV VSV checks out okay, it’s time to inspect the Exhaust Gas Control Valve (EGCV), which is very different from the bypass valve.
This valve is mounted to your primary turbo’s 02 housing and looks a lot like an internal wastegate. This unit blocks off exhaust gases to prevent overboosting conditions. If you have a problem with boost, this unit may be damaged or the flapper arm and valve inside the exhaust tube may be leaking or broken.
And finally the last part of our How to troubleshoot 2JZGTE Sequential Turbos Guide, is the Pressure Tank that’s located under the intake manifold. This plastic tank is responsible for feeding the IACV VSV valve as well as the EGCV valve.
To test this tank and the pressure that’s supposed to lead from it, check the pressure tank outlet near the front of your 2JZGTE crossover pipe. This vacuum hose is connected to a hard line thats commonly referred to as the “Y pipe” There are 2 vacuum ports on this pressure tank that run along the backside of your 2JZGTE. The lower port on the pressure tank runs to the IACV and EGCV for sequential control. The upper port runs to the front of the engine and exits from the Y pipe vacuum hose.
Inspect both hoses for pressure and check the pressure tank for any leaks that may cause intermittent problems with your boost control. The pressure tank is a common failure for those experiencing inconsistent boost levels, especially for JDM engines.
We hope you learned a thing or two in our How to troubleshoot 2JZGTE Sequential Turbos article, for more 2JZGTE articles like this subscribe to My Pro Street for more technical articles and how-to guides for DIY’ers!