Guys, leave now if techno stuff bores you.
I spent some time with a Garrett performance centre and had quite an enlightening chat about the current Garrett turbos and their issues.
This relates to the current crop with variable vane (VNT) technology operated by an electronic (i.e. non-vacuum) actuator - e.g. the one on my E280CDI etc.
Their experience is that the newer CDIs run so clean that failures are typically NOT due to fouling of the vane mechanism but are due to wear and tear in the electronic actuator resulting in loss of control of the position of the variable vanes.
The actuator cannot be replaced in the field and so a new turbo (£1,500 ish fitted) is the usual result with the actual turbo still mechanically fine.
Symptoms are some gentle power cycling under light load (think of a very slight kargaroo when on very light throttle) and then limp mode with a 2510-001 code (positioner signals fault). This code resets on engine off/on UNTIL 5 counts in one drive cycle - then it turns on CEL and needs STAR to reset. (2501-001 together with an over or under boost code, however, should direct you to all the usual candidates for over or under boost errors, many outside the turbo itself)
The actuator is a worm-drive motor with a PCM control circuit driven by the engine ECU.
At manufacture, the individual turbo has (I think) 20 vane-position settings programmed into the actuator, corresponding to 20 levels of increase in boost across the turbo - i.e. specific to THAT turbo. This calibration machine is NOT available to the field and so a new actuator (if it was available) can't be "tuned" to the old turbo.......a scrapyard actuator is therefore likely to result in over or under boost problems..
This all ensures that a relatively simple ECU map can be used to provide safe/predictable/progressive boost levels.....the ECU "talks" PCM (some models CAN) to the actuator.
So, over time, the worm drive motor wears, carbon from brushes is dusted around and eventually the feedback mechanism detects (a rotation sensor on the worm) that the worm has not moved accurately and quickly enough and so an error is thrown -> limp mode.
To check the fault:
Unclip the actuator arm (one circlip) and see if the vanes can be moved freely and without "sticky points across the full travel. If so, its not a vane problem.
Remove the actuator (2 bolts, the circlip and a connector) and check the wiring harness (its under the PCV pipe etc so it COULD be oiled up.....).
Take the top off the actuator (6 clips) and inspect the motor (leave the circuit board alone - its WAYYYY past any DIY soldering).
Chances are there will be brush carbon dusted around in there so liberally use isopropyl alcohol spray (Halfords contact cleaner) to hose the motor/brushes/comutator/work drive all clean (just think washing machine motor only smaller!). You can rotate the motor to clean it all as the electronics will "zero" it again when you turn on the ignition next.
Reassemble and test.
You will probably get a new life of 10s of thousands of miles out of the turbo but the motor might equally be beyond this spruce up from carbon damage or brushes/commutator too far gone......there are no spares and its assembled with no thought of sensible disassembly.
At least you will KNOW its time to cough up....
Discuss.....
I spent some time with a Garrett performance centre and had quite an enlightening chat about the current Garrett turbos and their issues.
This relates to the current crop with variable vane (VNT) technology operated by an electronic (i.e. non-vacuum) actuator - e.g. the one on my E280CDI etc.
Their experience is that the newer CDIs run so clean that failures are typically NOT due to fouling of the vane mechanism but are due to wear and tear in the electronic actuator resulting in loss of control of the position of the variable vanes.
The actuator cannot be replaced in the field and so a new turbo (£1,500 ish fitted) is the usual result with the actual turbo still mechanically fine.
Symptoms are some gentle power cycling under light load (think of a very slight kargaroo when on very light throttle) and then limp mode with a 2510-001 code (positioner signals fault). This code resets on engine off/on UNTIL 5 counts in one drive cycle - then it turns on CEL and needs STAR to reset. (2501-001 together with an over or under boost code, however, should direct you to all the usual candidates for over or under boost errors, many outside the turbo itself)
The actuator is a worm-drive motor with a PCM control circuit driven by the engine ECU.
At manufacture, the individual turbo has (I think) 20 vane-position settings programmed into the actuator, corresponding to 20 levels of increase in boost across the turbo - i.e. specific to THAT turbo. This calibration machine is NOT available to the field and so a new actuator (if it was available) can't be "tuned" to the old turbo.......a scrapyard actuator is therefore likely to result in over or under boost problems..
This all ensures that a relatively simple ECU map can be used to provide safe/predictable/progressive boost levels.....the ECU "talks" PCM (some models CAN) to the actuator.
So, over time, the worm drive motor wears, carbon from brushes is dusted around and eventually the feedback mechanism detects (a rotation sensor on the worm) that the worm has not moved accurately and quickly enough and so an error is thrown -> limp mode.
To check the fault:
Unclip the actuator arm (one circlip) and see if the vanes can be moved freely and without "sticky points across the full travel. If so, its not a vane problem.
Remove the actuator (2 bolts, the circlip and a connector) and check the wiring harness (its under the PCV pipe etc so it COULD be oiled up.....).
Take the top off the actuator (6 clips) and inspect the motor (leave the circuit board alone - its WAYYYY past any DIY soldering).
Chances are there will be brush carbon dusted around in there so liberally use isopropyl alcohol spray (Halfords contact cleaner) to hose the motor/brushes/comutator/work drive all clean (just think washing machine motor only smaller!). You can rotate the motor to clean it all as the electronics will "zero" it again when you turn on the ignition next.
Reassemble and test.
You will probably get a new life of 10s of thousands of miles out of the turbo but the motor might equally be beyond this spruce up from carbon damage or brushes/commutator too far gone......there are no spares and its assembled with no thought of sensible disassembly.
At least you will KNOW its time to cough up....
Discuss.....
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