second turbo not working

[mikeyh]

hi there i got my car back today and unfortunatley second turbo isnt working.

today the boost controller was reconected i believe its only connected to one of the turbos cant see any other pipes going to second turbo.

can any one help?

does the second turbo run off the first or does it also have to be connected to the boost controller

[Geezabloke]

Have u checked all the small hoses on top of the cam covers at ther rear?

Used to have one pop off now and then and had same effect?

Aslo check your actuators as these can fail.......

 

Dave :littled:

[CJ]

I would not mess about Mikey, I would take it back and get the garage to sort it out. You paid good money for the engine and fitting - you should not have to sort this out?

[terribleturner]

This was the little B%$£%$d that caused mt second turbo not to work. Check both ends are connected.

 

[JohnA]

That the one between the EGCV VSV and the EGCV actuator right?

[Suprasteve]

my 2nd turbo never kicked in when i split one of the pipes come off round the back of the engine (right handside). - you can just about see it but its very difficult to get your hand behind the engine block - especially when its hot !

 

but could be a number of pipes that cause the problem so best check them all.

[mikeyh]

ive inspected all the pipes seem fine but have noticed that the boost controller only seems linked to the first turbo.where is the second turbo pipe and second actuator pipe situated,if i find those two and t piece off of them into the pipes connected to the first turbo will this work?

[JohnA]

... but have noticed that the boost controller only seems linked to the first turbo...

 

 

That's how people connect them.

 

I took a good look at the workings of the Supra's sequential system, and apparently the 'common' knowledge that there is only one wastegate is not 100% correct.

 

The Supra has TWO wastegates until 4K rpm and only one (effectively) from there upwards.

The second 'wastegate' is the EGBV which acts as a wastegate for turbo #1 while the other turbo is off-line.

Both are pulsed by the ECU*, and I suspect that they both have actuators with springs of similar strengths (EDIT: the EGBV spring might be slightly softer, as it is fully open at 14psi, while the wastegate is at 17psi).

 

So when you fit a boost controller on the 'main' wastegate (of #1) you fail** to see any boost increase over stock below 4Krpm. The reason is that the 'other' wastegate bleeds off the extra gases.

The fact that it is downstream of #2 doesn't mean jack for #1, it still appears to it as a full-blown wastegate, upstream of the exhaust gases coming towards it.

 

However, there is a catch: You cannot always treat the EGBV as a wastegate, because from 3.5 - 4Krpm it also doubles up as 'prespooler' for #2. (from 4K upwards it doesn't really matter if it's open or closed, its effect on boost control is minimal) So the gases that you redirect from it (to make #1 boost harder at low revs) are taken away from #2's prespooling. Go too far and you end up with #1 boosting much harder and #2 kicked in the @ss to get up to that speed very abruptly. Double whammy.

Neither do you need the 'spaghetti' setup I've seen elsewhere on this site, or the dangerous mod shown on mkiv.com, or even this quite elaborate setup (it disconnects the EGBV from the pressure tank altogether, and uses a new, regulated boost source to pressurise the EGBV actuator)

A simple bleed is enough in my opinion.

 

 

I'll use this post as a basis to write up this whole operation for my website when I find some spare time....

 

 

 

 

*

as opposed to the intake and exhaust control valves that are either open or closed.

 

**

not on the UK-spec anyway, maybe the undersized wastegate of the JSpec leads to a slight boost increase, I'm sure that JSpec owners can help us fill this gap.