Now,
If the car still runs like crap, then it
can be one of the 4 items above.
1) Requires the removal of a lot of stuff to inspect the compressor blades. So let’s save that for last!
2) As also mentioned above, the really easy way to test is to pull the hose off the IACV after driving the car. I have actually had a release of air several hours after the car has been off. So it does hold air
very well. If not, look for a bad hose from the rear loom to the Pressure tank. Or check the pressure tank itself by reaching up from below and see if you can feel both hoses attached.
3) You can check this by either removing the DP or doing a visual, or by unbolting the 3 bolts that hold the EGCV to the turbo assembly. You will know if it has snapped off. You may even be able to see it if you wiggle the lever. Broken flapper arm is not that uncommon.
4) More rare, but I read about someone who went single because his turbos took a dump (he thought) and it turned out to be a collapsed inner wall. This is a common symptom, but not that common to collapse all the way closed.
http://www.97supraturbo.com/Seq%20FAQ/Corrugated.jpg
5) The IACV has a reed valve inside it. The reed valve is more for preventing back pressure. But there is a
valve in there, similar to the EGCV valve, and it has been know to to get loose (although the screws were “locktited” from the factory. If they get loose enough, it can “bind up” and not open. This is can be easy to see by removing the IACV actuator rod and just move the arm.
http://www.97supraturbo.com/Seq%20FA...ed%20Valve.jpg
Now, to elaborate more on the #2 taking a dump. Obvious death wine, smoke bellowing out the rear, metal on metal sound being reverberated through the heat shield, and a definite moaning sound. Another good reason on the temp TTC is because you can actually run the car at idle, and if the 2 actuators are open, it allows exhaust pressure to flow to the #2 turbine and spin up the #2. You will definitely hear a bad #2 in this case. Then you wouldn’t need to rev the car past 3800 to activate the #2. What can also happen is a bent or busted shaft. That is usually caused by a defective EBV. If the EBV has a defect, or a hose that has cracked or come off, it will never allow for any pre-spool. This means that at 3800 rpms when both the IACV and EGCV open, it is like opening the flood gates and all of the exhaust energy is thrown at the #2. Kind of think of it as a relay race with the handing off of the baton. If the #2 is just sitting there idle, and it gets blasted, it will most definitely get bent of bust. Not maybe right away, but if this continues to happen, it’s a matter of time.
A good tool for testing all of the actuators is a MityVac:
http://www.97supraturbo.com/Seq%20FAQ/MityVac.jpg. About $50. Has a gauge and can do pressure as well as vacuum.
Here is a link to a pressure testing system that a member posted awhile back. This is another way to check for leaks and lower turbo hoses.
http://www.supraforums.com/forum/showthread.php?t=78644
Other issues regarding boost.
A typical healthy OEM Supra will not feel the transition as prominent as someone who has a boost controller and fuel cut defender (BCC). Since the OEM boost characteristic is 8.8 psi to 10.8 psi, and the EBV holds it at about 10.2 psi, the transition isn’t that abrupt. If the EBV system is working properly, then there will be a dip in boost pressure of about 1-2psi. prior to 3800 rpms. The symptom of getting
near “0” psi at transition is an EBV related issue. The problem of have boost falling off as the rpms are increased is a Wastegate issue. Wastegates are notorious for taking a dump with the Supra. They crap out a lot. It could be a slight hole or crack in a vacuum hose. As the pressure rises, it opens, and releases the pressure that is needed to hold the wastegate actuator open. On the flip side, there are the ones who get too much boost. A good possibility is a cracked wastegate hose cap. It can be near impossible to see it. When you install an EBC, you need to put a small cap over the front facing actuator nipple and tie it off. It gets prone to heat and can actually pop off the tip enough so it “flaps” as the pressure rises. This causes “no” control of boost, or unlimited, because it can’t pressurize itself and hold open the wastegate.
Now, lets look a some actual scenarios and the possible fixes.
Here is an actual diagnose and fix from a member.
Symptoms: #2 Does not come online, boost falls off after 4.2k rpm.
Description of Unsuccessful Tests: No pressure release from VSV hoses after hitting .7bar 5 times and immediately stopping to pull VSV hoses to check for pressure release. After alot of testing, the IAC and EGC actuators/VSV's checked out perfectly. After a boost leak test, tiny amounts of air were found to be escaping from the IAC VSV connections, which caused a tiny amount of boost fluctuation. 2 zip ties were put on every vacuum connection coming from the pressure tank outlet line. VSV bypass TTC and ETTC did not do anything. Each actuator would hold pressure perfectly. the entire system seemed to be in perfect condition.
Successful Diagnosis Test: I decided to pressure test the post pressure tank line and components via the wire loom nipple that feeds to the IAC VSV. Pressure escaped from the y-pipe line, which was unplugged from the barb. Immediately realized the pressure tank was failing or the inlet outlet lines were switched. Visual inspection of the p. tank inlet connection revealed that the rubber vacuum line was partially blown off due to pressure build up.
Fix: Swap the pressure tank inlet and outlet lines, which a mechanic had switched during turbo assembly reinstallation. The lines can be swapped at the pressure tank without removing anything if you have small enough hands, which I do not. A guy at my mechanics garage happened to have some tiny hands and was able to swap the lines
By: Stu Hagen
http://www.97supraturbo.com
How the 2JZ sequential turbo system works
