No 2nd Turbo or Lag even in Temp TTC

Hi guys, I've done my fair share of reading so far and have narrowed it down but would really appreciate your thoughts on this. I've actually got an Aristo but shouldn't matter in theory.

I picked up the car 2 weeks ago and noticed that it seems to have been BPU'd in Japan, boosts to 1.2 bar visible on Greddy Boost Gauge, set using a HKS EVC but the boost peaks around 2500 rpm and drops to 0.6-0.8 bar at around 4000RPM in Sequential. I thought this was strange and it seemed to be that it's likely only running on the 1 turbo and at that RPM has gone past the efficiency of that turbo.

I set to putting it in temp TTC by swapping the vac lines (snapped the end off the IACV VSV nib oops) and was worried I'd get no boost at all. No it boosts just like it did before, boost comes on about 2500rpm still and drops off the same, no distinct change to sound or anything.

I'm assuming this is likely to be a vaccum leak somewhere stopping the EGCV actuator from opening and allowing the second turbo to kick in? Does this seem the likely scenario to you guys? I'm going to take a pump to it on the weekend to see if it's seized because this car has been so well looked after and the engine bay is mint but it could have been sat for quite a while before being imported. If the actuator does indeed open fine, where is the most likely place to find the leak? I've read that the pressure tank is an area that could be prone to leakage, is there anywhere else I should check that could be causing this scenario.

Thanks in advance.

Matt

does it make any noticeable noise when it reaches 4,000 revs? there is sometimes a problem with the EGCV sticking, have you tried moving the actuator arm by hand to make sure it moves? (it can be quite hard to move).

http://www.mkivsupra.net/vbb/showthread.php?35926-The-sequential-system

Thanks, I've read through this - hence the fact that I'm assuming it's EGCV, just wanted to see if anyone else has had a similar experience.

The only strange noise I've noticed is what kind of sounds like a venting noise, like I don't know.. if you open the oven when it's hot? but that's not specifically at 4000 rpm, sort of like an air venting noise I guess. I'm going to give the actuator arm a good fiddle when I get my car back tomorrow as It's currently in for a wheel refurb.

You shouldn't be seeing anything like that boost pressure at low RPM unless someone has modified things. Normal first turbo only pressure is around 0.5-0.7bar at that RPM. There are ways to put a bleed valve in near the back of the engine to raise the pressure on the first turbo, not done it myself and can't find the detail, look for anything hiding on the vac lines back there that doesn't look stock.

Losing boost pressure at cutover is a classic indication that the second turbo isn't spinning up, so when the cutover happens you lose all your pressure back down the intake via the second turbo. Although if that were actually the case your TTC should produce nearly no boost. Weird.

I'd suggest starting to look for leaks in the vac system as well as testing all the VSVs actually work. The idle air control valve has also sometimes been fingered as a cause of problems, essentially anything on the vacuum system might be wonky... This page has the pressures that each actuator should open at and how to test, pain in the arse to do it on the car but might be a last resort for a really stubborn to diagnose fault.

You shouldn't be seeing anything like that boost pressure at low RPM unless someone has modified things. Normal first turbo only pressure is around 0.5-0.7bar at that RPM. There are ways to put a bleed valve in near the back of the engine to raise the pressure on the first turbo, not done it myself and can't find the detail, look for anything hiding on the vac lines back there that doesn't look stock.

 

Losing boost pressure at cutover is a classic indication that the second turbo isn't spinning up, so when the cutover happens you lose all your pressure back down the intake via the second turbo. Although if that were actually the case your TTC should produce nearly no boost. Weird.

 

I'd suggest starting to look for leaks in the vac system as well as testing all the VSVs actually work. The idle air control valve has also sometimes been fingered as a cause of problems, essentially anything on the vacuum system might be wonky... This page has the pressures that each actuator should open at and how to test, pain in the arse to do it on the car but might be a last resort for a really stubborn to diagnose fault.

The car has definitely been BPU'd the boost reaches 1.2 bar happily which is set by the HKS EVC, I'm not sure what else they've done but it's running a Greddy FMIC and HKS Intake so it seems like the previous owner in Japan had something in mind. thanks for your help - I'll take a look at the IACV.

Like ianhid says, you shouldn't be seeing 1.2bar on the first turbo, no matter whether it is bpu or not. bpu should be 0.7'ish bar first turbo then 1.2bar when the second comes in, not the other way around I'd start by checking the vac hoses for dodgy plumbing.

Like ianhid says, you shouldn't be seeing 1.2bar on the first turbo, no matter whether it is bpu or not. bpu should be 0.7'ish bar first turbo then 1.2bar when the second comes in, not the other way around I'd start by checking the vac hoses for dodgy plumbing.

If you set the boost pressure to 1.2 bar on the boost controller and, lets say the EGCV is stuck, then surely it'll reach that 1.2 bar regardless? That's why that's my current suspect at least, whether the pressure isn't actually reaching the actuator to open it or or the actuator itself has somehow become locked in place is another question.

Check for any error codes on the ECU

There is a wastegate on the first turbo, that should be opening regardless of what the EGCV is up to. Try dropping the boost controller to 'off' or whatever option it has to not interfere with the wastegate pressure and see if the first turbo behaves more sensibly. If that checks out, the next step is to trace through all the vac lines and make sure they connect up to the right locations. Once that's proven out, test the actuators and VSVs. Do it nice and methodically, it's a complicated system and not something you can just scattergun fix.

Problem is now solved, the hose had come off the back of the pressure tank and it looks like the owner in Japan tried to T piece from another pipe over to it as the original pipe had a snapped piece of plastic inside it. Have managed to get it connected up how it was originally intended and now have boost turbos working in TTC with boost coming on at the right time. Only issue now is the boost spikes like crazy, peak of 1.4 bar and then the wastegate opens to drop it back to the set 1 bar. I've ordered the replacement IACV VSV to put it back into sequential anyway and will take it from there.