[VladPC]

I'll try that next week... I have to go to my mechanic to borrow the hand vacuum pump again.

This is what I have tested:

Also the other pressure converter for the wastegate has the same values on the gauge when is beeing operated by DIS software.

The electric valve holds vaccum and goes from 0 to almost 15 inHg when activated by DIS.

[nicklockard]

Hmmm, watching with interest. My turbine changeover valve doesn't start actuating until 17 inHg and is done by 23 inHg. Total movement is about 16mm. It does hold vacuum. Wonder if this is my problem.

[Yozh]

What I noticed:
-System vacuum should be over 25inHg. Yours seems to be just a tad over 20. This is low.
-ISTA test cycles the turbo switchover but should be full vacuum on and off, yours seems to only get up to 15inHg
-Turbo switchover will start moving on 5inHg, it’s normal
-I’m curious of your EL valve tied up by the positive terminal. Is it not connected?

[VladPC]

I tied the EL valve there. It is plugged it. From the outlet of the vacuum canister there is more then 25inHg. The pressure converters only allow at the outlet just over 20inHg. When I actuate the turbine switchover valve with ISTA the pressure converter does not have enough time to get pressurised...that's why it only reaches 15inHg.

[Chief Orman]

I would spend all my time on checking the goddamn turbo hoses and IC for a crack...then use the strongest clamps and hoses you can buy from the likes of ATM

[VladPC]

I have a new intercooler that has been installed last month and a new turbo hose, BMW oe.

[VladPC]

Still haven't solved it. Yesterday I went to a mechanic and checked the position of the turbine changeover valve rod. I thought it wasn't positioned correctly...but it was.

The issue is that untill 2000rpm, with the foot to the floor (no kickdown), actual boost pressure on ISTA is only 1500-1600 mBar (specified is 3000mbar). That is 0.5-0.6 bar without atmospheric pressure. Anywhere above 2000rpm actual pressure is the same as requested pressure.

I tried one thing though. I put it in manual, went for 3'rd gear and accelerated from 1100rpm. As soon as I went over 2000rpm and the boost pressure acheved 3000mbar as requested, I upshifted very quickly to 5th or 6th (can't remember now) with the foot to the floor (no kickdown). The rpm went down to 1100 and the actual boost pressure was 3000mbar and requested was also 3000mbar.

So the car is able to produce 3000mbar (as requested when you put your foot down) at 1100rpm. The problem is that it can't be achieved. It can only be done as I explained earlier.

Any thoughts? I would much appreciate if someone could help me with this one.
It's a bit complicated...I'm now suspecting a bad ecu tune...maby the pressure converter doesn't release vacuum when it should, in order to open the flap for the exhaust gases to travel to the big turbo...

Even when driving around town at low speeds (40-60 km/h) in D, the requested boost pressure is 1700mbar and it only does 1100-1200mbar.

[robnitro]

Your shift to 5 test holding boost makes it seem like the small turbo is not working at all or the switchover valve is stuck open which reduces flow to the hp turbo at low rpm. How is boost at high rpm?

It doesn't sound like the big turbo is having a problem getting flow but if you give it flow too early you take away the flow that should spin the small hp turbo.

[VladPC]

Boost at high rpm is perfect. 3000mbar all the way to 4800rpm when it shifts next gear.

Took it for a spin just an hour ago, away from the city.

I have experienced a lot of wierd things...for example. I stopped and started from 0 km/h in first, changed at about 2000 rpm into second and as soon as it engaged second gear I pushed the pedal to the floor (no kickdown) and nothing...all the way to 4000 rpm. And when I say nothing I mean absolutely no boost. Only just before it would shift to third It gave "a explosion" of boost all of a sudden. This happened above 4000rpm.

I also have experienced that I have to wait a lot for the boost to come on...the feeling of turbo lag. Anywhere in the rev range and only if I step on the gas pedal all the way down all of a sudden. If I feather the throttle, pushing it gently it would accelerate harder.

[torqueisking]

To attempt isolation of the potential culprit, I would mechanically isolate and secure the compressor bypass and the turbine bypass valves in the closed position (max small turbo contribution). If the low RPM power returns, it's not the small turbo and your bypass valves are operating properly.

Next step is to reconnect the bypass valves to the vacuum canisters and electrically "hard-wire" the pressure converter and changeover valve to again close both bypass valves. It appears as though the pressure converter needs >95% duty cycle (use 12Vdc) and the changeover valve can be disconnected to achieve this. In other words, the DDE is no longer controlling these valves. If low RPM power is still good, the issue isn't vacuum related.

I'll likely going through the same process this spring to diagnose my low RPM power issue although my symptoms are consistent and no codes appear.

[Yozh]

I’ll throw more ideas here. Low boost at low rpm. Typical issues are discussed already. From vacuum leaks to malfunctioning pressure converters or leaking switchover valves to broken nipples to leaking vacuum actuators to stick valves (turbo switchover, compressor bypass, wastegate) to misadjusted turbo switchover rods. But then you can also have sensor issues like boost sensor, MAF, EMP. The. Boost leaks. Then exhaust leaks before sensor. Then plugged exhaust in cases of left SCR in place. And further, blown small turbo. Then torque converter issues. And finally leaking valve cover gasket. Or a shitty tune.

[VladPC]

@torqueisking
If i'm going to force the exhaust gases to the small turbo (i could block the bypass plate to direct air flow to the small turbo), I'm not going to achieve anything because the small turbo doesn't do absolutely anything in terms of Pmax. It'll just (probably) make somewhere between 1500-1700 mbar all the way to 4800rpm because all the Pmax power is acheved by the big turbo which is feeding air in the "inlet" of the small turbo (when the bypass plate is closed).

So it's absolutely necesary for the turbine switchover valve to slowly move to relaxed position, thus allowing exhaust gases to flow to the big turbo and precharge the fresh air into the small turbo.

I could try to force the bypasa plate to closed position. Thank you for the idea.

@Yozh
Thank you for the ideas...by the way my car is german edition (european car). It does not have any of the SCR-s and useless pollution restrictive things (egr, dpf, swirl flaps) and so on.

I now have an appointment at a software tuning shop. We'll see how it goes. I'm going to film anything I can under the hood (vacuum actuators) when the car is beeing tested on the dyno. I will also ask for each and every LOG to be sent via my email. This way I could also send the LOGS to...Ecumap and speak to the guy...I have seen the result of his work and I'm pretty pleased for what I have seen.

[robnitro]

No, it does do pmax itself at low rpm range!

the small turbo does all the boost up to around 2k or so.
All exhaust should be going through small turbo in that low rpm range.

After that both turbos are contributing until 3k or so.
Exhaust goes to both turbos.

Then after that, only the big turbo is working.

[RL18]

A visual of what robnitro is saying and some other useful pictures:

[robnitro]

Thanks, for the diagrams. I couldn't find them in my stash!

I was close from memory but a few corrections to my post.

At low rpm if the turbine bypass for small turbo is open you will not have low end boost. This is the #8 on the last drawing which is the wastegate for the small turbo. This opens at higher rpm to allow the big turbo to flow freely. If yours is being stuck open- you won't have boost down low.

Also, if the #7 is open- the small turbo compressor side will not be putting boost into the engine. That's only open when at higher rpm to let the big turbo flow without being choked by the small turbo.
If you have this one open , you also will not have low end boost.

The reason why the big turbo is not used for low rpm is that if you try to create high boost at low rpm from a big compressor, you will have stall/surge issues. Being a wastegate turbo, it won't get there because not enough flow.
Smaller turbos can create a lot of boost at low rpm, but choke at higher rpm.

[VladPC]

Went to the dyno... I was pretty damn sure it was a tune problem but, of course, it wasn't. I asked the tuner 3 or 4 times if the tune is ok and he said it was ok (the one existing on the car).

He tried to add more fuel at low rpms....(i'm guessing increasing the mg/stroke)..to try to help the turbo to spool quicker from lower rpms but with no success. He also tried to modify the map of the pressure converter that controls the turbine changeover valve (tried to direct exhaust gasses earlier to the big turbo) and the result were very poor (gained only 15-20 Nm of torque low down).

Eventually he gave up saying he couldn't do absolutely anything. He didn't pinpointed the exact problem which really disappoints me. He told me only general stuff (change the turbo, check the turbine changeover valve and so on). He also said that the car starts to pull hard from 2300 rpm...the point where the turbo (or turbos) are at full boost.

Can someone please explain how to adjust the turbine changeover flap? I'm now thinking it's bad adjusted. The way i repositioned was this way.
- Loosened the bottom nut (the one that is closer to the front of the car)
- Screwed it the top nut (the one that is closer to the windshield) with a considerable number of threads...almost to the end of the thread, towards the vacuum box
- Attached a vacuum hand pump to the vacuum box nipple and applied vacuum until the rod if fully towards the windshield (maximum gasses to the small turbo)
- Bring the metal thingy (i don't know how to call it...basically the small metal thing that is between the two nuts and which controls the direction of the exhaust flow) all the way towards the windshield as far as it will possibly go.
- Bring the two nuts and tighten them to the metal thingy (the one mentioned above)

If i do it this way, I don't have 16 or 23 threads...as most of the guys here have... from the bottom of the rod to the top (from the front of the car to the windshield). It's 10 or 11 threads max.

[RL18]

I doubt the adjustment will help. I did the same and the issue didn't change. You really gotta make sure you've changed or checked EVERYTHING in the vacuum system, intercooler boots, intake manifold, swirl flaps, etc.

I've been changing things for months. It's crazy frustrating. And as of now my vacuum system is all new parts and new intercooler boot on hot side. I'm going to be changing the valve cover gaskets... I have a hunch that that's my issue and I never pickup on the beginning sign of it. I know I should anyways because I always see blue smoke on initial start up.

[VladPC]

I have checked everything on the vacuum side. I have even made a smoke tester, home build. It's not a vacuum problem. I have tried a new pressure converter and an electric valve but with no success.

It's exactly the same problem as our friend here:
https://www.e90post.com/forums/showthread.php?t=1465068

From 2500rpm the car accelerates like crazy.
I would much appreciate if someone could help me adjust this turbine switchover valve.

From what our friend said...looks like JR Auto fixed his car. And if I'm not mistaken Andrew is working on these type of engines and as far as I know he is a member of this forum.
I could really use his expertise on this one.
I'm talking about him :

[RL18]

Take a pic of yours. I loosened the bottom bolt with 10mm stubby then you should be able to spin the top bolt by hand. Make sure you mark the thread you started on so you can track your adjustments.

You said you only have 10 threads? Or threads showing? I would shoot for around 16-23 threads. I'm at 23 currently

[VladPC]

10 threads showing, beeing exposed.

I don't know if it makes any difference but my car is an european model, brought from Germany...could it be different on these models?

I'm also taking in consideration that the reason for turbo lag is due to waiting for vacuum to deplete from the vacuum box (of the turbine changeover valve) in order to open the flap for exhaust gases to go to the big turbo.

[RL18]

Okay yes. Move that up. Loosen bottom bolt (towards front of car) then spin top bolt (towards the trunk) up. Start at 16 see how it feels then you can adjust up as needed!

That bottom bolt looks like it been replaced too. Atleast mine doesn't have a built in washer on the bottom bolt.

[robnitro]

The vacuum box does not deplete, the solenoid is what opens the lines to air or vacuum.