Guilietta QV turbo problem

[k1w1_123]

I apologise in advance for the long-winded post but I dont want to waste anyone's time by leaving out anything important. I am also well aware I will be telling most of you how to suck eggs with my descriptions of how I understand the turbo controls operate, but I needed to write down the thought processes that have led me to here..

My 1.8 QV has recently developed an issue with the turbo. Initially, after a cold start the turbo did not work until I revved the engine high enough in 2nd or 3rd gear for the turbo to jump into life. After that, it seemed to function properly, until I let it cool again. It felt like it got stuck somehow, and once there was enough airflow it was able to overcome the friction and spool up properly. This has got progressively worse until now the turbo does not work at all. I have put a USB camera down the inlet tract to see if the turbo is turning but the results are inconclusive: with the MAF disconnected to get the camera down the intake the engine will not run for more than a second or 2, but in that time the compressor wheel does start to turn. I have made a few test runs with MultiECUScan and the highest pressure recorded by the MAP sensor is 998 mbar, just a tiny fraction LESS than atmospheric. Going uphill in 3rd or 4th at 4000 rpm with the thottle wide open the MAF sensor reads 210 kg/min.

If driven sympathetically the car runs without any fault codes but if it is lugged uphill in too high a gear at insufficient revs (wife driving) it will come up with fault code P0240-72 "Turbocharger pressure control - Actuator stuck open". Elearn offers the following diagnosis...
Check for loose connections on the supercharging pressure sensor
Check for the presence of loose connections on the Powertrain Control Module
Check for seepage in the air duct from the turbocharger to the throttle body
Check that the supercharging air bypass solenoid valve is working correctly
All these checked with no faults found.

I have made the following checks on the turbo itself
1) With air intake and exhaust piping removed the Turbo spins fairly freely at both ends. Both wheels are firmly attached to the shaft and there is no radial or axial play in the bearings.
2) Lubrication oil feed pipe is clear of obstructions and the gauze filter is clean.
3) Air filter is clean and inlet air flow is unobstructed.
4) Pressurising the inlet piping by connecting low pressure air (15-20 psi) at the inlet flow sensor shows only a very minor leak where the plastic inlet trunking connects to the aluminuim inlet pipe. This is upstream of the turbo so of no consequence.
I do have some reservations about how freely the turbine rotates when in situ with the oil cold. I can flick it around easily with my finger but it doesn't keep spinning.

I then turned my attention to the bypass valve. This is a spring loaded diaphragm design held closed by the spring and opened by manifold vacuum. The bypass valve's operation is managed by the solenoid diverter valve mounted on the driver's side front of the engine and is controlled by the engine management system. When the solenoid valve is not energised (normal condition) the bypass valve actuator is connected to the inlet manifold. The bypass valve is closed in normal running and will be automatically opened if a manifold vacuum exists. The actuator is also connected to a vacuum pump via a 3-way valve. In the event of a cut-off, or when the over-pressure limit is reached, the solenoid valve is energised by the engine management system and the bypass valve is opened by the vacuum pump. Failure of this solenoid valve will normally result in the car operating normally EXCEPT the bypass will not open in an overpressure event.
Bypass Valve Checks:
1) Remove and dismantle valve, ensure spring is intact and diaphragm is undamaged, reassemble.
2) Vacuum test bypass valve and tubing to solenoid valve - holds vacuum
3) Confirm solenoid valve is operated by ECU
4) Road test car (gently!) with diverter valve connection open to atmosphere. In this state the bypass valve will be held closed by the spring thus eliminating any possibility of the bypass valve passing air. Use caution so as not to overpressure the system while the waste gate is disabled.
More Checks just to be sure:
5) Vacuum test tubing from solenoid valve to vacuum pump - holds vacuum
6) Confirm free airflow via tubing from manifold to solenoid valve
7) Connect a power supply and energise solenoid valve
Vacuum test tubing from solenoid valve to manifold - holds vacuum
9) Confirm free airflow via tubing from solenoid valve to vacuum pump
10) Confirm solenoid valve is operated by ECU
No faults found with any of these checks

The final possibility was the waste gate which is held shut by a spring loaded diaphragm actuator and pushrod, and opened by boost pressure. The waste gate's operation is managed by the solenoid valve mounted on the radiator support on the driver's side and is controlled by the engine management system. In normal operation the solenoid valve is energised and compressed air from the turbo outlet is returned to the inlet via a small tube. In this condition the waste gate actuator is isolated and the gate is held closed by the spring. When the valve is de-energised, compressed air from the turbo outlet is fed to the waste gate actuator and the waste gate opens. In this condition the connection to the turbo inlet is isolated. Failure of this solenoid valve will normally result in the waste gate allowing exhaust gases to bypass the turbine at moderate turbo pressure.
Waste Gate Checks:
1) Pressure test tubing and actuator from solenoid valve outlet. Actuator commences to open at around 0.6 to 0.8 bar. This means the waste gate cannot open until turbo outlet pressure exceeds 0.6 bar
2) Pressure test tubing from turbo inlet and outlet to solenoid valve. To avoid having to disconnect the inaccessable inlet side tube, disconnect both tubes from the solenoid valve and pressure test end to end.
3) Confirm solenoid valve is operated by ECU
4) Road test car (gently!) with waste gate actuator connection open to atmosphere. In this state the waste gate will be held closed by the spring thus eliminating any possibility of the waste gate allowing exhaust gases to bypass the turbine. Use caution so as not to overpressure the system while the waste gate is disabled.
Still nothing found.

I am at my wits end! Does anybody have any idea what the problem could be PLEASE!

[Colin Edwards]

The turbo impeller should spin easier / less drag when the engine oil is heated/viscosity reduced. 
A noticeable difference between cold and hot? 
How much axial movement in the impeller shaft?