E60: New engine tune-up Part 4 - Waste-gate + Pressure-converter.

After the last tune-up [here] the stifled boost remained. Up to about 2000rpm the power was ok, but after that, when the real boost is expected to come in, it wouldn't. Rev and noise would rise with no acceleration. All that exhaust gas was just escaping through an open waste-gate, signified by a constant 'dump-valve' style hiss. At this point i really got my head around the vacuum-actuated turbo setup and tested the vacuum-tank [3 in diagram] and each hose individually for leaks, finding nothing. In a last ditch attempt to try and get the E60 boosting again I replaced both the waste-gate [with the slightly shinier one from my old turbo] and the electronic pressure-converter that controls it [1 in diagram].

This finally gave some results. Boost is now back and the long drawn-out hissing has gone, though there is still a short gap in between low and high boost. If you are rolling slowly in 2nd or 3rd gear and plant the throttle, the car surges forward then hesitates with a hiss for a moment before full boost comes in and the hiss stops abruptly, however this is only noticeable when accelerating in this way. A slower rate of acceleration gives an almost unnoticeable transition to the point where full boost can be applied and the car pulls away. This is also true when cruising a bit faster in 2nd or 3rd, where the waste-gate has had time to shut and full boost acceleration is instant. This to me suggests there is still a vacuum problem and I will have to re-check the hoses going under the steering to the engine-mounts, as they're the only bits I haven't been over a dozen times. The car is useable at full boost now, so I know the new engine is running as it should and capable of giving the power I was used to before the troubles, but pulling away fast in 2nd from traffic lights is a bit long-winded and I find myself changing up to 4th pretty sharpish before I feel confident enough to grill it. Really though, how often do I need to pull away fast without waiting in gear for a second before doing so? Perhaps I'm asking too much...

The next engine jobs will be focused on smoothing the rough idle, though in the meantime I threw in a mixture of Cataclean and Wynn's Injector Cleaner to see if that helped - half of each bottle added to 30 litres of diesel twice. I'm sure it did some good to the engine, but apart from making it a bit peppier for a couple of weeks there was no improvement to the idling situation. If the vacuum problem is not to blame then one or more injectors could be failing. There may even be a problem with the DDE controller, though this is extremely unlikely.

Next jobs:

• Redo smooth-running measurement.
• Replace / recode injectors if necessary.
• Check oil on rocker-cover. Is it leaking from 10mm injector-studs to head?
• Re-check all vacuum-tubing and replace where possible.

Future things to do / buy:

• Rear ball-joints / ball-joint tool. [Advisory on last MOT].
• Swap glow-plug module.
• Intake manifold ring profile-gaskets.
• Rubber rear exhaust-hanger.