On Fri, 01 Aug 2008 22:05:36 +0100, Colin Stamp
Well, I had some time to do a bit of poking around today, so I tried
taking out the air filter - no change, so that was that off the list
The vacuum pipes for the dump valve looked a bit dodgy, so I thought
maybe they ware causing the valve to leak air round the bypass loop. I
tried it with the control pipe to the valve disconnected and plugged,
which gave me low boost right through the rev range, which was
inconclusive. So instead, I plugged up the bypass pipe. That gave me
the original symptoms back, so I guess the dump valve and it's control
system is off the hook too.
It could still be the dodgy vacuum tubes though. They share an inlet
manifold tap with the fuel pressure regulator so I guess, if they were
leaking, they might cause knock through low fuel pressure.
I've also finally RTFMd a bit, and I found a section entitled "Air
mass limitation" which has a graph showing the torque reaching its
maximum value at 1.8K RPM and then starting to ramp down at 5K. That
doesn't really tie up with what I'm seeing now *or* how I remember it!
I think I'll just change the vacuum hoses and then forget about it,
whether it fixes it or not. I'll be trading it in soon anyway...