Engine: T5/R T5R Boost….again!

[Pupbelly]

The ongoing boost issue lingers on. Having replaced all vacuum lines with silicone, all intercooler hoses with DO88 silicone, boost control valve, throttle position sensor I have now moved to the actuator.

I have bought a pressure /vacuum pump. After pumping the actuator it was opening at around 3psi. So a bit of twisting of the rod and according to the pressure pump it now starts to open at 6psi.

BUT!! Driving the car still only takes the boost gauge to barely into the white on the dashboard gauge with no thrust still. WTF?

What on earth is going on?? The turbo is spinning and active I think because I think I can hear it when you rev the engine but why is there no boost pressure registering at the actuator? It is meant to have a new Forge bypass valve, could it be at fault? Really getting pee’d off with this all now!!

Anyone got any thoughts please??

[Luxobarge]

I feel your pain Mark.

Rig up a way to do some sort of pressure test on the intercooler? - I mean test that it's not leaking badly?

Did you get anywhere with testing/changing the knock sensors?

[Pupbelly]

Hello again, I’ve not gone down the knock sensor route yet as that involves a lot of surgery. I was hoping a intercooler hose kit may help but no. So a vacuum/pressure kit has been purchased which if nothing else has allowed me to test the actuator. Next test will be the turbo bypass valve. It should be fine but you never know!

After that maybe the intercooler will be next to check but it doesn’t sound to leak at all.

All bloody annoying!!

[JohnM 855 T5R]

Hi Again,

Your saga continues........
Assuming your knock sensors are ok (you should get a fault code if they aren't), the possibilities are dwindling. As far as you have gone, I'm left with these thoughts.

1) Have you used an independent gauge hooked up to the vacuum tree to check actual boost pressure. Daft though it might sound, your dash gauge might be faulty and your expectation of a T-5R's urge might be too great and the boost is actually fine. If nothing else, it will give you an actual pressure baseline to work from. If you really are only getting a couple of p.s.i, that's a catastrophic boost loss of around 9 p.s.i. which should be easy to identify as not a lot will cause that. The small vac lines for example won't cause that pressure loss as the amount of air they can pass is limited and the turbo can push enough air to certainly give you more boost than you seem to be getting.

2) The Forge TRV you have might not be seating correctly or sticking causing a large boost by pass but again, the by-pass line is only of small diameter and I doubt it could pass all that air. Do you get any turbo "chatter" when you lift off quickly? You shouldn't if all is well with the TRV.

3) The wastegate is letting by due to poor internal seating (it's not a rare occurrence and a new wastegate is the only cure)

4) A split in the intercooler (but to be honest, I'd expect to hear that amount of air leaking). Remember, if you decide to pressure test the intercooler, you will get some pressure leakage as there is a deliberate drain hole to drain out condensation. (This is what I mean about a hole somewhere having to be big to cause your lack of boost as this small deliberate drain hole doesn't give rise to boost pressure issues.

5) Crack in one of the "hard" turbo pipes (again, it would have to be a large crack and I think you would hear it).

6) Faulty signal from the auto transmission control ECU limiting the boost. (I'd expect some fault code for that).

7) And this is the biggy - your turbo is simply knackered and just not capable of putting out enough air. Could be blade erosion, blade damage, bearings not running freely so it doesn't spin up enough or a crack in the turbo housing (pretty common problem as you can see from the Wheeler Dealer T5-R episode where they had b****r all boost due to a cracked housing).

I'm leaning towards a turbo problem at this stage.

Regards
John

[Pupbelly]

Hello John, thank you for your reply. No fault codes are shown, no chatter when lifting off the throttle, no whistles or howls that would indicate a major leak in fact I’d go as far as no assistance at all. My Impreza had the same turbo and my wife has an Abarth 595 so I know what should be there when the car is meant to be spooling up.
I could go down the road of a separate boost gauge but I just know it’s not right and a long long way off the mark.

I’ve established the wastegate operates and based on my pressure gauge the wastegate should now hold until circa 6/7psi but there is still no additional reading on the boost gauge. Im tempted to wind it up even further but I’ll refrain for now. If the turbo bypass valve is ok (I’ll do a suck/blow test on it and see if it leaks) then there’s clearly some other issue which is beyond my capabilities and I’ll have to either get the turbo checked or something. The thing is it has a receipt from last year where the “core” has been replaced along with the Forge bypass valve to in theory that rules out a duff turbo. Surely it would have been checked before a rebuild?
I just want some oomph! It is basically a big lazy Volvo at the moment which is not why I bought it!

Is the bypass valve easy enough to get at. I gather one of the three bolts is tricky??

[JohnM 855 T5R]

Originally Posted by Pupbelly

I’ve established the wastegate operates and based on my pressure gauge the wastegate should now hold until circa 6/7psi but there is still no additional reading on the boost gauge. Im tempted to wind it up even further but I’ll refrain for now. If the turbo bypass valve is ok (I’ll do a suck/blow test on it and see if it leaks) then there’s clearly some other issue which is beyond my capabilities and I’ll have to either get the turbo checked or something. The thing is it has a receipt from last year where the “core” has been replaced along with the Forge bypass valve to in theory that rules out a duff turbo. Surely it would have been checked before a rebuild?
I just want some oomph! It is basically a big lazy Volvo at the moment which is not why I bought it!

Is the bypass valve easy enough to get at. I gather one of the three bolts is tricky??

The whole wastegate has 3 critical components - a diaphragm, a spring and the waste gate valve itself. The boost pressure acts on the diaphragm and pushes a piston against the spring so moving the actuator rod connected to the wastegate valve itself. Some use a vac signal on the other side as well.

First, the diaphragm can leak, in which case they don't operate as soon as they should and you can get overboost

Second, the spring can relax and it opens at too low a pressure causing underboost. This is what you are trying to compensate for when you adjust the rod. It is the wrong thing to do. It may give a temporary (and marginal) improvement but its risky. A whole new actuator assembly for your turbo can be had for about £50 comprising the housing, diaphragm, piston and spring.

Finally there is the actual wastegate valve which the actuator rod is connected to at the turbo end and acts upon (not part of the actuator assembly). The actuator rod acts on the wastegate valve to open it when boost reaches the maximum desired level (the ECU via the TCV tells it to do this). Excess pressure is bled off (a lot of people don't realise that even the humble TD04HL-15 will push enough air to exceed 20 p.s.i. boost as I found when my TCV stopped working). If the wastegate valve is not seating well, it will bleed off pressure ALL THE TIME even if shut, causing low boost. It is this seating that I'm referring to!.

Go search the web for diagrams and how wastegates work.

As for your Forge TRV, they are pretty reliable. By all means take it off and inspect it - it's a pain with one of the bolts, lots of swearing, perseverance and skinned knuckles. Make sure the correct spring is fitted (a green one) and the o-ring is sound.

Regards
John