I took my tdv8 RRS to dyno and I found out the car doesn't keep up with stock parameters. Instead of having ~600Nm of torque since 2k rpms it turns out that I get ~400Nm and it keeps it like that up until 3.5k rpm to give it a little bump at the end to ~450Nm. The first thing that comes to mind is not enough boost, so I decided to take my cheap elm327 tool to just check intake pressure. Poor boost log covers with low torque. I attached dyno and boost charts.

I took car to several workshops and all they could say is that there are no errors logged by ecu that could indicate that something is wrong. Car runs pretty ok, there is no smoke etc, but honestly I imagine I'd expect a bit more from tdv8. I don't want to leave it like that but on the other hand I couldn't find anyone with a strict strategy on what to check/fix/replace to get the job done.

So I'd like to ask community for help:
1. Is tdv8 a sequential twin turbo? I know 3.0v6 is sequential but I couldn't verify if tdv8 is. If the answer is yes maybe one turbo would be not working properly (the one for low range rpms). On the other hand some errors should be raised to ecu, right?
2. I guess that due to lack of clear error codes and torque characteristic intake leaks could be eliminated, could someone prove me wrong?
3. Is there anyone having intake pressure logs? Or anyone with tdv8 and a simple diagnostic tool that could make such log? At dyno they read the stock map and said the relative boost pressure should be around 2 bars from 1.8rpms up to the top. Mine is nowhere near that number, I wonder how it looks on some healthy rrs.
4. Anyone having any ideas regarding what to check? Shall I get rid of egr first (egr diagnose says its fine). Or maybe replace maf/map sensors?

Any help appreciated.

The TDV8 has port deactivation as the intake ports are set up to give different characteristics at different engine speeds. At low speeds, one intake port is effectively closed, leaving only a swirling intake port active. Above a certain rev point, the other port is opened to give intake filling.

There is a vacuum pipe connected to the intake filter box, it's just behind the pipes leading from the filter box to the turbos. Make sure it's connected. This pipe is involved in activating the port deactivation.


Then check that the pipes from the intercooler aren't split. A small split can have a big effect and doesn't necessarily throw up an error code, strangely.

Alternatively, the EGRs might not be working correctly. Again, this might not throw up an error code if it's a minor error, although it will give reduced performance. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

What are the MAF sensors reading at idle, and 2500rpm?

Thank you for your answers.

I've checked the vacuum pipe connected to intake filter box, it sits pretty tight. It goes from there to small separator and vanishes somewhere in the dark abyss of the engine bay. I guess it goes to both turbos, as you wrote. As for the other splits that are probably not so easy to verify by myself I would assume mechanics that I went initially did their job, they said all seems to be fine. But of course you never know... I will write it down on the list of things to check, I want to create some kind of strategy, go to verified people with proper diagnostic tools and ask them to follow it.

As for MAF sensors I can only get readings from single bank using my elm327.

On cold engine:
RPM: 768
MAF: 22 g/s
--
RPM: 2522
MAF: 77,5 g/s

On warm engine:
RPM: 656
MAF: 12 g/s
--
RPM: 2515
MAF: 82,5 g/s

Should I expect some specific value, maybe some specific value under load? I guess I could try to switch them and log readings again to verify if values are the same. Or maybe buy some more sophisticated diagnostic tool

I bought sdd and did some logging.

First MAF measurements as requested:

At idle:
MAF1: varies between 33-37kg/h
MAF2: varies between 28-33kg/h

At 2500 RPM:
both MAF1 and MAF2 around 130-140kg/h

I also played a bit with logging data coming from different engine sensors. All tests I did were on 3rd gear in command shift mode, getting to 1.5k rpm and pushing gas pedal to the max up until 4k rpm. I noticed that:
1. Actual and demanded absolute manifold pressures are the same, max around 2.2 bars. Shouldn't it be sth around 3.2 bars? Could someone verify?
2. Throttle position sensors show value around 5% all the time. Is this correct? Throttle pedal angle is fine.
3. I can see "commanded boost actuator control" and "boost pressure actuator position". Are these related? Commanded is ~70% and falls down to 45% when engine load increases. The latter one is zero all the time.
4. At max acceleration:
- driver requested torque: 620Nm
- indicated engine torque set point: 640Nm
- torque requested after load transient corrections: 513Nm
Seems fine I guess ?
5. EGR is 45% and drops to 5% as soon as I start accelerating. Seems fine as well?

Can anyone help? Does anyone knows what is desired max manifold abs pressure?

Siemens injectors  Joe

Do you think my issues can be related to injectors? Why? Is there any way I could verify/diagnose that?

I had one injector replaced half year ago due to leak, however the car was lacking power even before.

The injectors play a very important role in engine performance. Have a look at this injector report and you'll see that they give different deliveries at different loads as well as various levels of back leak.




My advice would be to get them properly tested, if only to rule them out. Joe

Maybe eventually I will get injectors to check, although this is quite an operation.

On the other hand I noticed torque converter fail symptoms (rpm fluctuations). I had my gearbox oil changed 3 months ago so I guess I will have it replaced. Do you think this could also be the reason for the lack of power problem?

And yet again, does anyone knows expected max absolute manifold pressure? Is 2.3 bars ok?

Just for the sake of anyone interested. Torque converter was the cause. I got +100Nm at 2,5 rpm after replacement and it is smooth power delivery now.