Boost cut?

[frp]

As some of you may know ive had a problem with the car for quite a while. after swapping all ignition parts, altering gaps altering the fuelling on the safcII i was a bit stuck. today i took the car out and decided to look at the acvr (boost) side of things.
My mate watched the screen whilst i put 3rd, 4th and 5th through their paces. the only noticable thing was the boost peaks higher than usual. used to peak around 1.67 -1.73 max boost is 1.5/1.6ish. its now peaking 1.85 and today as high as 1.89. i know this is peak and not max. the boost settles and holds perfectly 1.54/1.56 to the limit.
I put the avcr to the graph mode and recorded the boost and when the usual problem occured after a while. the boost did nt slope off it spiked/peaked and went vertically down to the bottom of the graph. as in 90deg straight down and levelled for a few seconds then straight back up :doh:
So does any one have an explanation for this or even think this is the cause or just a bi-product of the mysterious event :der:
I also altered the F/B settings for 3rd and 4th (downward) it seemed to make the car less viscious but didnt solve it. also reduced the duty in 3rd and 4th but the result was the same.

cheers
steve

 

[geetee]

Maybe that boost spike is causing the engine to detonate briefly, which the ecu is picking up on and retarding the ignition?

What's the scale on the graph? i.e. what value is the bottom of the graph? is it actually zero? If so then clearly something is happening mechanically to release the pressure.

I don't know enough about the avcr to help I don't think - but does it connect to the det sensor circuit at all? If it does, does it have some kind of protection mechanism to kill the boost if it sees the det signal go too high?

All speculation