So what have you done to your car today?

[TheBoy]

Surely not much point in having Bank 2 sensors on a V6 if the only work at higher rpm

Eh? Why not.  The ECU still needs to know what's happening...

[Doctor Gollum]

Presumably both banks are pulling in air to combust the fuel regardless of rpm

[Marks DTM Calib]

TOPix does seem to imply there is a throttle valve in the throttle body.  Not sure why on a diesel, but it is French/American, so all bets are off . Need to look further, but I'm convinced I'm missing some documents from workshop manual.

The throttle is used mainly for stopping (anti shuffer), it gits fiddled with a bit for DPF re-gen and EGR

[Marks DTM Calib]

Presumably both banks are pulling in air to combust the fuel regardless of rpm

Twin 'parallel' independent turbos, one per bank  (rather than a twin series turbo running on all banks), they will spool differently with slightly different boost pressures so you weight the air independently

[TheBoy]

Presumably both banks are pulling in air to combust the fuel regardless of rpm

Twin 'parallel' independent turbos, one per bank  (rather than a twin series turbo running on all banks), they will spool differently with slightly different boost pressures so you weight the air independently

The secondary turbo gets no airflow under the RPM is high, a set of valves shut it off, so as to increase air speed through the variable vane primary turbo.

What I'm not sure of, because I can't find the right doc, does that mean that the feed to the secondary turbo is stopped, and all air to the cylinders (via the primary turbo) is fed via a single MAF ?  Which could explain why one MAF has a high airflow and the other looks idle.  Which allows me to rule that out as a fault

[TheBoy]

Found the doc



So looks like until it decides that its better to spool up the secondary turbo, that MAF will not see any airflow.  So the low MAF readings are to be expected.

[TheBoy]

For my benefit, doc is called

FUEL CHARGING AND CONTROLS - TURBOCHARGER - TDV6 3.0L DIESEL  TURBOCHARGER - SYSTEM OPERATION AND COMPONENT DESCRIPTION

[Marks DTM Calib]

Yes based on that you would expect low readings on one and high on the other, should change with revs.

On the above there is likely a variable vane turbo which will boost at low revs and a waste gate controlled turbo which spins at higher revs.

You could momentarily actuate the waste gate and check the MAF reading increases

[TheBoy]

Yes based on that you would expect low readings on one and high on the other, should change with revs.

On the above there is likely a variable vane turbo which will boost at low revs and a waste gate controlled turbo which spins at higher revs.

You could momentarily actuate the waste gate and check the MAF reading increases

Primary turbo is indeed variable vane, secondary is wastegate.

Sadly, my lead for SDD does not allow "Measurements" (aka live data to you and me), hence stuck with looking at what was recorded at the point of the DTC being raised.

[Doctor Gollum]

Looking at that diagram, each side feeds a turbo, one for lower rpm and one for higher... Presumably to reduce lag and broaden the torque curve

Is this done for packaging purposes? Would've expected to see a small turbo feeding a larger one on each bank...

[Marks DTM Calib]

Looking at that diagram, each side feeds a turbo, one for lower rpm and one for higher... Presumably to reduce lag and broaden the torque curve

Is this done for packaging purposes? Would've expected to see a small turbo feeding a larger one on each bank...

That would offer no benefit (four turbos are not needed to deliver the required torque) whilst adding cost, weight and reducing reliability 

Also, RPM is not actually that key to any of the operation, the variable vane can boost independent of RPM and then the waste gate derivative can add extra if needed. Modern turbo setups are designed such that they respond to demand 

[Raeturbo]

On the 3.0 xf only the big turbo is used when plodding about, the small one coming in to assist on demand.

[TheBoy]

On the 3.0 xf only the big turbo is used when plodding about, the small one coming in to assist on demand.

Which is the same setup on the XJ tractor.  Secondary only spools up when the Primary starts to run out of puff

[TheBoy]

Feel we* are making progress on this now.  Gone from depression yesterday at the thought of replacing the inlet manifolds - which is probably a job too big for me currently - to a more optimistic view it might be something else.

Having looked at videos of split manifolds, I can see no sign of my insulation moving on lift off.


*Me doing the monkey work, Marks "Remote Diagnostics" DTM Ltd pulling the strings

[Jimbob]

Got an MOT pass on the E Class.

Just advisories on front and rear disks, so need to weigh up options there