Yet another 2nd Turbo problem

[Guest AMW]

Jap Spec 93 Auto, totally stock.

 

Hi Guys, I am hoping there is somebody out there who has figured out how this sequential turbo system works. I have read lots of other threads and every time I think I understand it I read something else that makes me more confused.

 

My problem is that at 4000 rpm I loose all boost, this is quite a rapid loss of boost, needle drops straight to zero.

I have checked the hoses as best I can, pressure tested the system from turbo outlet to throttle body and all is fine. I can see the Intake Air Control Valve moving (I was quite surprised that this starts opening at low revs) and I can see the Exhaust Gas Control Valve open at around 4000rpm, this seams to be when I loose the boost.

What I don't understand is how I am loosing the boost generated from the 1st turbo, even if there is a problem with 2nd turbo, where could that be going? The only way to get any boost back is to let the revs drop right down (and I assume then the Exhaust Gas Control Valve shuts) and then I get turbo 1 back (until I go over 4000rpm).

 

So, if I understand it correctly, I know turbo 1 works fine, I know the Exhaust Gas Control Valve opens which should make turbo 2 spin so no matter what the other valves are doing I cannot see where my boost goes to. Even if turbo 2 wasn't pre-spooled surely after a second or two it would be up to speed and creating boost along with the already spinning turbo 1?

I doubt it is the valve which has been referred to as BOV as this appears to work purely on pressure and not related to rpm, the boost starts to climb steadily up to 0.5bar, stays there and then suddenly drops to zero when I go over 4000rpm (I don't know the accuracy of the gauge but it is consistent). There has been no unusual noises, smoke or any like that. I am really puzzled.

 

Any advise would be much appreciated.

 

Cheers

 

Adrian

[dwayne]

check this thread for a similar problem/fix http://www.mkivsupra.net/vbb/showthread.php?t=224896&highlight=boost+drop

[Guest AMW]

check this thread for a similar problem/fix http://www.mkivsupra.net/vbb/showthread.php?t=224896&highlight=boost+drop

 

Thanks dwayne,

I had already seen that thread but it didn't have much in the way of answer, it just said it was a vac pipe. I have now sent a message to the guy who stated it and hopefully he will know which of the maze of pipes it was.

Still don't see where the boost could be going.

 

Cheers

[Suprab1]

I remember something about there only being a wastegate on one turbo.

 

Maybe it's on turbo 2 & is stuck open? That would explain why the boost goes completely when the valve opens to the 2nd turbo.

 

Or maybe i'm daft

[dwayne]

if its not a vac pipe that what my next guess only prob i ever had was the one where if you lift your foot off and hit it again the boost came back but after a while it fixed itself.

[ShamelessTT]

Almost sounds like hitting fuel cut ....but without the >1bar boost......does the car loose power all together in a sharp drop? or just the boost go and the power go slightly...

[pistonbroke]

See problem 2 in the first post in this thread.

 

http://www.mkivsupra.net/vbb/showthread.php?t=35926

[Guest AMW]

I remember something about there only being a wastegate on one turbo.

 

Maybe it's on turbo 2 & is stuck open? That would explain why the boost goes completely when the valve opens to the 2nd turbo.

 

Or maybe i'm daft

 

Hi Suprab1,

There does appear to be a wastegate on turbo 1. It is possible that it is opening but it cannot be stuck open as I would have no boost at any time. I can see the VSV for it but the pipe just goes into the turbo so I cannot see any kind of actuator so I can't tell if it is opening.

[pistonbroke]

EGCV valve mate, as per my previous post. I believe its one of the two VSV's underneath near turbo one, it's the bigger of the two.

[Guest AMW]

Almost sounds like hitting fuel cut ....but without the >1bar boost......does the car loose power all together in a sharp drop? or just the boost go and the power go slightly...

 

Hi ShamelessTT,

I did to start with think it was a fuel starvation issue, even fitted a new fuel filter. It doesn't die altogether, just stops accelerating (well most of the acceleration). After fitting a pressure gauge at the turbo output it shows that the boost disappears. The engine will still be doing over 4000rpm so I figured there should still be turbo boost pressure even if there is a fuel issue. My thoughts were, if the engine is still doing a high rpm, there will still be exhaust gases of some description going past the turbos so surely there should still be a boost pressure?

 

Cheers

 

Adrian

[Guest AMW]

EGCV valve mate, as per my previous post. I believe its one of the two VSV's underneath near turbo one, it's the bigger of the two.

 

Hi pistonbroke,

Thanks for your reply,

The first one refers to problem 2 from another thread:

 

"Problem 2: I don't get a 2nd turbo rush, and as soon as I should it dumps all boost instead.

The IACV is opening but the second turbo isn't spinning. All the air boosted by #1 turbo now has an easy path back to the non-pressurised side of the turbos via a non-spinning #2 turbo. In effect, it all goes 'backwards' through #2 instead of going into the engine. You'll maybe see .2 or .3 of a bar of boost but that's about it.

 

This usually means the EGCV isn't opening. The turbo can't spin as it has no exhaust gas flow path. Although annoying, this won't do long-term damage as #1 turbo won't generate much boost because the engine loses a lot of power, so no overspeeding or overheating.

 

This has all the same symptoms and when I first started trying to figure out my problem I thought this was it. The major difference is that I am sure my EGCV is opening, therefore I know the VSV actuator etc are all working and the exhaust gases are flowing past the 2nd turbo. I do now have a horrible feeling that the turbo maybe seized which I think would have to same effect as a non opening EGCV

 

Cheers

 

Adrian

[dwayne]

have you tried the TTC mode? that might rule out a few things

http://www.internetwork.org.uk/mechanical/ttc/ttc.htm

Edited October 10, 2010 by dwayne (see edit history)

[Chris Wilson]

Has the arm fallen off the EGCV?

[Guest AMW]

have you tried the TTC mode? that might rule out a few things

http://www.internetwork.org.uk/mechanical/ttc/ttc.htm

 

Hi dwayne,

I haven't tried TTC yet, I guess that might help. From what I gather it makes the EGCV & IACV both open as soon as any boost pressure is generated. I know that both the EGCV & IACV are opening so I didn't think it would help. I will give it a try if nobody has any other ideas. I guess it is possible the ECU is opening these valves at the wrong time and the TTC would bypass that.

 

Cheers

Adrian

[Guest AMW]

Has the arm fallen off the EGCV?

 

Hi Chris,

It does seem has the symptoms of the EGCV not working (assuming this is the one in the exhaust manifold just upstream of the oxygen sensor). I can see the actuator moving and the arm is securely connected to the EGCV. There is also a noticeable change in the exhaust sound so I assume that proves that the EGCV is opening. I am really confused to where to boost pressure could be going to.

 

Cheers

 

Adrian

[Nic]

See problem 2 of Ian's thread HERE it seems to describe exactly what you are experiencing.

 

Has the 2nd turbo been checked for damage?

 

Service Manual Turbocharger System may also be of help.

[Guest AMW]

See problem 2 of Ian's thread HERE it seems to describe exactly what you are experiencing.

 

Has the 2nd turbo been checked for damage?

 

Service Manual Turbocharger System may also be of help.

 

Hi Nic,

pistonbroke had already suggested "problem 2". I am sure my EGCV is opening.

The turbo has not been checked, there has been no strange noises, smoke etc. Is there an easy way to see if it spins freely without stripping it down?

Many thanks for the service manual, looks like I will have to work my way through it and test everything as I go if nobody has any other ideas.

 

Cheers

Adrian

[Guest AMW]

I have been reading through the service manual that Nic kindly posted. I have started by trying to test the things which can be done without too much dismantling.

I am starting to suspect the exhaust bypass valve actuator.

 

Please bear with me while I try to explain.

If I understand it correctly this should open when turbo 1 is up to speed and before the Exhaust Control Valve. It seams to only move a tiny tiny amount. The service manual says to test block of one hose and pressurize the other to 1bar and check that it has fully extended. This does happen BUT it only starts to move at 0.7 bar and fully open at 0.8bar (moves much more). I never get that amount of boost so how can it possibly open? The manual also says that at 5600rpm there should be 0.6-0.75bar, thats with both turbos which still wouldn't be enough. As I expect the actuator is just a diaphragm and a spring I cannot see how it could get stiffer. I know the diaphragm is ok as it holds pressure.

 

Has anybody tested their EBV actuator? If so at what pressure did it open? (very easy to test without any dismantling)

 

Has anybody heard of the actuators getting harder to operate? (needing more pressure?)

 

any help would be greatly appreciated

 

Cheers

Adrian

[BOB B]

Hi Adrian.

 

I have only just seen this thread, I had the same problem, when people talk about the Exhaust Gas control Valve it can be a bit confusing because even if this valve can be working the actuator, (low down, under the turbos slightly nearer to number 2 turbo) may not.

 

My symptems matched yours pretty much, except, is there a noticable increase in air movement sound, a louder sucking/wushing sound when you tried to go faster?

 

My problem was sorted by fitting a second hand actuator, hate to say it but a major job, so I hope it isn't this.

[Guest AMW]

Hi Guys,

I haven't made much progress trying to figure out why all my boost disappears at 4000rpm.

As previous said I suspected that the EGBV was not opening so that turbo 2 was stalling so I manually opened this. All what happened was the boost dropped to about 0.2 bar and still no 2nd turbo.

I have now done the parallel turbo conversion (vac pipe method) and now I have no turbos at all.

First off it was as normal until about 3200rpm when the boost climbed to about 0.3 bar then dropped. The exhaust note changed to be more of a growl and from then on I got virtually no boost at all. The EGCV and IACV are both slightly open. I am guessing now that turbo 2 is not spinning and allowing the boost from turbo 1 to go backwards through the IACV and past turbo 2.

Does that sound possible? I figured if turbo 2 was seized I would have got some kind of warning, like a noise or something. What else could it be?

I would appreciate any suggestions before I try taking it apart. Is there an easy way to see if turbo 2 is spinning?

 

Cheers

Adrian

[Branners]

my first thought when I saw this thread was blown second turbo. Still think it is that. First turbo builds boost, at 3500rpm it goes to bring the second turbo in which has failed (being ceramic it physically disappears from the shaft) and so the boost just goes straight out the second turbo.

 

I would certainly be looking at the 2nd turbo as a failure. Perhaps check the exhaust for bits of ceramic turbo if they havent already all blown away.

[Guest AMW]

I suspect "Branners" is right about the 2nd turbo. My only doubt is that there has been no noise or vibration. If the turbo had destroyed itself I would have thought it would have been noticeable?

 

Looking at second hand turbos, does it matter what the spec are, eg Jap/UK, VVTI or not, Aristo/Supra? Are there any differences?

 

Cheers

Adrian

[Hoppy]

I would also say the 2nd turbo is at fault.

 

I had the same symptoms, when my 2nd turbo gave up on me. What was happening with mine was: The 1st turbo would boost fine up to 4000rpm, but once the valve for the second turbo opened, all my existing 1st turbo boost pressure would instantly divert, and escape backwards through the inactive 2nd turbo.

 

Although, i could clearly hear the air pressure whoosing back out of my air intake. I also found my 2nd turbo's hot side components when i removed my exaust cat.

[Nic]

Looking at second hand turbos, does it matter what the spec are, eg Jap/UK, VVTI or not, Aristo/Supra? Are there any differences?

 

The UK turbos and the J-spec turbos have different bolt pattern onto the manifold.

 

J-spec VVTi and non-VVTi turbos are the same fitment on the Supra and I *think* they are also the same on the Aristo but not 100%.

[Guest AMW]

Thanks to "Hoopy" & "Nic" the replies,

I still think turbo 2 has failed BUT I don't get the whoosh sound that "Hoppy" mentioned. As I don't see any other path for the turbo 1 boost to go I assume it must be going backwards through turbo 2. Maybe if it is seized rather than destroyed the air could still travel backwards though it but with some restriction limiting the whoosh factor? Sound possible?

 

So I guess I need to buy a J-spec turbo.

 

Cheers

 

Adrian

Edited October 28, 2010 by AMW
spelling (see edit history)