Quote:
Originally Posted by spannerrash
My gut feeling tells me that turning the engine on the starter motor with no plugs in at all, should generate enough pressure to activate the tensioner.
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This is correct. When I test engines on the stand I can hear when the oil pressure is coming up because the valvetrain quietens down significantly just before the pressure switch activates and turns on the light in my test box. From a completely cold start it can take a minute or more of cranking to build pressure, but once its done it the first time, subsequent attempts are just a few seconds.
I suspect you may well be chasing a ghost, but it does sound like you've done enough test cycles to be sure about the figures. A hot compression test would be interesting.
There's not really any way to measure the tensioners as they are so crammed in there. The main thing would be to check the marks on the ends of the cams line up with the arrows on the head but that would need cam covers off. The ECU knows the position of the adjusters from the cam position sensors on the inlet cams. In VCDS it will show you how much adjustment its putting in to get the cams where it wants them. Typically I aim for 0-1° after a timing belt replacement.
One thing does spring to mind - how are you preventing the engine from trying to start during the compression test? If the ecu is powered up and attempting a start cycle but, say, has no fuel pressure if you pulled that relay, then it might be messing with the signals to the cam adjusters and inadvertently changing your values. I couldn't explain why it would do one and not the other, but if the ecu is still awake it might be worth disconnecting the adjusters and seeing if that makes any difference to the readings.
I'll disconnect the crank sensor if doing a compression test in the car as then the ecu doesn't know the engine is turning so doesn't try to start.