Re: MB engine overboost

[Orin Eman <orin@WOLFENET.com>]

> Joe Lowe again.  One thing I forgot to mention in this mornings e-mail was 
> that when I get overboost the engine usually pinks/knocks very loudly aswell 
> but not allways.  This may narrow it down ?

That's expected.  When my 5k was overboosting, it would knock very loudly
once it got over 2 bar or so.

>From your and Phil's description, it sounds like the wastegate is
staying closed.

Initially, I suspected the ECU programming, but since Phil says it has
'gone away', perhaps not.  That would leave things mechanical which
expand/contract with heat or lack of it...

So, you have the wastegate itself, the wastegate frequency valve and
the hoses leading to it.

The first thing I would try would be to remove the hose from the top
of the wastegate, plug the hose and leave the wastegate top open.
See what happens.  If the problem goes away, check those hoses aren't
trapped/restricted and perhaps try replacing the frequency valve.

Another likely problem is that the wastegate itself is sticking.
I bought a used one that was completely seized.  Lots of carb
cleaner followed by WD40 freed it up.  I'd think it would be
more likely to get gummed up in the UK than here in the USA due
to the lack of O2 sensor and richer mixtures allowing more
carbon deposits.  I'd take the wastegate cap off, take the spring
out and see how easily the wastegate moves.  If you lift the
cup up it should fall back with virtually no resistance.

Orin.