BPU made no difference to bhp or torque

[Homer]

Just to add, even before BPU you should see 0.76 bar of boost, this is the out of the factory boost. The fact it's dropped means two possible things:

1) The restrictor is FAR too small (Which I doubt given that's it's come from Whifbitz)

2) There's something else holding back the boost (be it 2nd turbo, wastegate, IC, etc, etc)

 

I'd honestly be looking for an existing problem, but before all that eliminate the restrictor ring with the test that Scooter suggested (It's the easy first step).

 

This is how BPU should look, the pickup from the 2nd turbo should be very visible (It's a 13 year old picture so apologies for the quality). We didn't have smart phones in those days, just print outs and a scanner!

[samdale]

I'd honestly be looking for an existing problem, but before all that eliminate the restrictor ring with the test that Scooter suggested (It's the easy first step).

 

Finally someone without a file in their hand

[The Raven]

Id still look at the pipe connecting the turbos, Mine had collapsed and was causing BHP issues before they where changed, in affect it was acting as its own RR

[mellonman]

Id still look at the pipe connecting the turbos, Mine had collapsed and was causing BHP issues before they where changed, in affect it was acting as its own RR

 

this is a good shout but if you haven't changed all your vac pipes I would start there, also the stock side mounts can leak boost as well as many of the connections so a boost leak test would be also a good idea too

[Mont]

Decided to try the car with the restrictor ring out. After a few tentative drives I gave it a few hard runs where it would consistently hold 0.8bar (rather than 0.7). I did see 0.9bar for a split second once.

 

I’ll have to have a look at this turbo pipe next as it certainly starting to look like a restriction or issue elsewhere.

[mellonman]

for sure a issue somewhere else then , without the ring I could make 1.4 bar

you have probably seen this but here it is anyway http://www.mkivsupra.net/vbb/showthread.php?35926-The-sequential-system

Edited September 1, 2018 by mellonman (see edit history)

[Scooter]

http://www.mkivsupra.net/vbb/showthread.php?343594-sequential-issue-and-going-ttc-ideas-please&highlight=sequential

 

And this thread, I would do the link pipes, you could cut them off and fit some silicone tube to test (while waiting for new ones to arrive). If they have collapsed internally (will almost certainly will have to some degree) it may cause a restriction but I am not sure it would limit boost like it has?

 

I would be tempted now to put the ring back in as its not the cause and it''ll get you back 100% safe and you will notice the change when you fix the boost issue.

[JasonR24]

Sounds like you have no second turbo and your first is overboosting. Check all the hoses at the back of the engine, mine was the pressure tank hose that goes to the second turbo.

[Mike2JZ]

Check that your exhaust backbox baffles have not collapsed and causing excess back pressure.

[Homer]

Decided to try the car with the restrictor ring out. After a few tentative drives I gave it a few hard runs where it would consistently hold 0.8bar (rather than 0.7). I did see 0.9bar for a split second once.

 

That's exactly what occurs when the 2nd turbo is not coming online, your dyno graph matches this scenario (The dip in power at 3.5-4k is due to mapping when the ECU expects pre-spool, then full spool to occur, it'll look the same whether #2 is coming online or not). There are some very good suggestions in the posts above this so for sure you should check all these.

 

I would also suggest you try True Twin mode as a test as that should bypass several of the VSV's that can cause the 2nd turbo not to spool. Again, it's not a permanent solution, it just helps diagnose what might be causing it.