Re: MB engine overboost.

[Greg & Britt <image_one@earthlink.net>]

GT
84 5KT
87 5KCST
Phil Payne wrote:
> 
> In message <34A79555@smtpgate.mavericks.bt.co.uk> "Lowe, Jonathon, LOWEJD" writes:
 <snip>
> As a note to other readers - the MAC11/MAC12s that control the I5s with
> hydraulic tappets dating from 1988/9 _do_ permit a degree of overboost during
> initial acceleration.  Scott Mockry has some logging equipment and has produced
> traces of this phenomenon, and there is clear provision for it in the ECU code.
> 
> This is _NOT_ what we're talking about in 'MB warmup overboost'.  In this, the
> car takes off like a tweaked Sport or an S1 - only to hit a brick wall seconds
> later when the fuel pump cuts.  It's _very_ frightening if you're passing a
> long truck on a short road.  My guess is that the engine goes to over 300bhp
> for one or two seconds.

While screwing around with a method of variable pressurizing the “back
side” of the WG to control
boost I got the exact same type performance on my KH. It would run like
a scalded cat on part throttle and would hit overboost immediately if
the throttle was opened further.  Unfortunately I did not have test
instrumentation to measure boost differential across the throttle body.

This is basically how the MC has slight control over boost, when WOT
occurs you get the WGFV supplying manifold pressure to the back side of
the WG to raise its’ operating point.
The MB problem sounds like it might be a firmware glitch when in warm-up
mode, operating the WGFV full on. Need you the LED tester connected at
all times
to monitor its’ operation. ( I am making the assumption that the MB has
the same
control mechanism as the MC.)
You guys that know better can tell me I’m all wet. {:-)

GT
84 5KT
87 5KCST