Interesting story and totally in agreement Sizewell. I didn't realise until now (despite having read this thread a few times over the last month or so) that this is how the new powerflex rear bushes came to be. Congrats
Thank you for that. Glad to hear you got your problem sorted without too much financial damage.
I am still taking in the improvements I am seeing on the Q4, some subtle, some obvious and will report later. I just feel like "The Cat that got all the Cream".
However, I include a document for your and others perusal. I intend to contact Alfa Tech about this as to me it seems so glaringly obvious now. If they can point out the error of my ways, then I would be grateful for their contribution. However, I won't hold my breath for such a unique event.
Design Failings of the 3.2 V6 Engine.
Alfa Romeo must have realized there were issues with a common oil pump that not only had to supply all the bearings, journals, camshafts and the high pressure JTS fuel injector pump and the tensioners, but also the cam shaft advance / retard voids. This is clear as they made a token effort to overcome them! By this I mean, “Why otherwise would they fit non return valves/check valves into the cylinder heads, specifically in the galleries which feed the cam shaft bearings and the advance / retard mechanisms?” It may well be that the pump was adequate for bearings, journal, camshafts, tensioner and JTS pump, but not the “Cam Shaft Advance / Retard Mechanisms” as well!
Why not? Because the engine oil pump is at the remote end of the galleries which feed the camshaft advance/retard mechanism. These mechanisms have huge voids.
When the engine is switched off, or at “Tick – over” the camshafts are “Locked”, in the case of the inlets, at maximum retard and the exhausts, maximum advance.
These positions are ideal for starting the engine and also for meeting emissions regulations. But the engine can't do any practical work at these settings. That it why it is so easy to stall the engine at low revs when pulling away. So once the Throttle is depressed, the ECU must adjust the camshafts to optimize power delivery. At this point the camshafts become “Unlocked”.
As can be seen from the sketch of the cylinder head, Non return valves ensure the “Inlet Camshaft Retard Voids”, remain filled, whilst the Exhaust Camshaft Advance Voids” also maintain their fill, courtesy of these same check valves.
Unfortunately, as soon as the engine is persuaded away from tick-over, the camshafts “Unlock”. This immediately vents the previously filled voids to the “Drain”. But the oil in the galleries between the non return valves of the cylinder heads and the camshaft advance/retard mechanisms is minuscule compared to the size of all the camshaft voids; inlet camshaft needs to advance and exhaust camshaft needs to retard. “In all there are Sixteen of these voids that need to respond to the ECU's demand for advance/retard”. “At a time when Oil Pressure is virtually non existent”.
The top timing chains and guides will be fine as they have just been drenched in oil from the camshaft drains. But the bearings, con rods, tensioners and JTS pump will be screaming for oil. Of course the ECU won't see a problem as it's oil pressure sense is from the oil pressure switch just after the oil cooler/filter assembly. The inertial created by cold oil in the galleries will ensure the Oil Pressure switch will almost immediately operate as soon as the ignition button is pressed. But the oil pressure, where it is required; at the bearing, journals and JTS pump will remain lower than it should be until the camshaft voids have filled to concur with the ECU demands for timing change. This could be a maximum of 50 degrees for all four cam shafts, which because oil will follow the path of least resistance, is an unacceptably long period, during which the bearings are being starved.
The more enthusiastic the driver will result in this scenario being played out continually throughout it's driven life.
No where near as important, but non the less two other crucial factors arise from this fundamental flaw:-
a.) The hysteresis introduced due to Oil Pump to Cam Shaft Advance / Retard Mechanisms: “Oil Flow Inertia”, means the car can never achieve it's maximum acceleration; the delay between what timing the ECU wants to employ and the camshafts ability to respond will inevitable mean the car is not as quick as it could be. *** This is now evident from my earlier observation, about the cam shafts advancing when I held the throttle in second or third gear. The delay as they came in is indicative of the Hysteresis***
b.) This very same hysteresis probably suppresses the cars ability to achieve better fuel consumption, as it is too slow to respond to changes in engine load when on journeys. It could be as much as 4 to 5 mpg.
It is my intention to fit an oil pressure accumulator, to the cylinder heads. This will be done by removing the screw-in Blanking Plugs for the Camshaft Advance/Retard Galleries, just after the non return valves. All four camshafts will have individual feeds, of suitable diameter to ensure they suffer no pressure attenuation. These four feeds/hoses will come from a common manifold, which will be attached to oil accumulator pressure vessel, mounted somewhere under the bonnet.
The system will pressurize to at least that of the engine oil pressure pump and should sustain it between variations in primary oil pump pressure due to engine speed. The Non return valves in the heads should provide this function. I am not sure about the size of the accumulator yet, perhaps a two quart device and hopefully, preliminary testing will confirm a supplementary pump is not required.
This technique I intend to try first as it is the one that is least intrusive. I shall monitor the cam shaft gallery oil pressure to try to determine a trend. However, It is essential I should, on start – up,
allow the system to fully charge, whilst the camshafts are still in the “Locked” position. This means, staying off the throttle for a couple of minutes. Once the system is charged, assuming the check valves are “sound”, pressure should be maintained and the engine oil pump will have less work to do on start up.
PS the sketches did not attach so will try to send separately.