Re: MB engine overboost.

[Gerard <gerard@poboxes.com>]

Hi!

Well, I might as well jump on this thread. Mine has overboost
problems with the MC motor of 89/90, car is 200t with auto tranny.
As for recurring problem, well, I can do it anytime anybody wants
me to. Half throttle, just over 3000RPM, watch the boost, goes
all the way to 1.6 and that's that. Odd thing is that I'm up at
altitude with the atmospheric pressure 0.2 bar lower than the coast
and about a week ago I was at the coast and enjoying the extra
pressure but never saw the boost head over 1.3 bar and that was
with the pedal just off the kickdown switch and really gunning
it. Now I can give just over half throttle getting the car to
accellerate and the boost will actually rapidly climb to 1.4 and
over and then the accelleration begins. I back off though, I've
had the fuel shutoff happen 2 days ago and I don't want to feel that
again.

Known problems with the car is a hole in the exhaust just before the
last box with the hole slightly larger in diameter than the exhaust.
Split T-piece for the crankcase and valve cover breather pipes (can't
afford to fix right now, may just seal it up with masking tape).
Scratching sound coming from the bottom of the car at the location of
the alternator, but can't pinpoint it with all the belts there
doing their own scratch. Multi-function temperature sender also
corroded off about 4 weeks ago, I then made up wires for 4 clip
connectors and put them in place of the corroded plug and the gauge
has worked ever since. Using Duckhams QS synthetic as well, about
2.5 months now, the oil pressure drops to below 1 bar at times, but
no warning signals and I've determined from the list that that is
normal for synthetic oils.

I checked the fault codes yesterday. System comes back with 4444 signal
indicating all is fine. ECU is MAC13A, cutoff is set to something like
1.66 overboost with normal wastegate pressures around 1.4.

My hard accelleration is shot, as putting the foot down while cruising
along has become a big "no no" and will send the boost way up there
at 1.4-1.6 bar. Accelleration on mild throttle, gently seeing the
boost go to 1.4 and over will feel better accelleration happen at
1.5 and 1.6, but then ofcourse the cutoff happens.

I will need to check the wastegate sometime. What is the procedure
for checking it and cleaning it? If the wastegate diaphragm is split
could it cause loud high-pitched whistling? This is my first turbo
car (and first car for that matter) and I've never done work on
such things, so detailed help on removing the gate and checking it
will be really appreciated. I also looked at the vacuum lines on the
WGFV, I've replaced one about 1.5 months ago and was happy to be
getting all my boost back (the pipe was mainly dust :) ). The other
lines look fine, but when I get some money I will replace them with
newer, thicker Goodyear tubing as a precautionary measure (and as
a measure of consistency to keep the engine bay clean looking :) ).

And the exhaust, could a hole in the pipe before a box cause so much
better flow that the turbo really spins up faster and boosts more?
I've never had more than 1.1 bar of boost here at altitude and that
was another situation running to the redline with the pedal denting the
footwell bodywork (:)). That's was ofcourse last year, before this
situation I'm running now. I will be patching the exhaust this
afternoon, hopefully some rumbles and hisses will go away.

Oddly enough, the car sure does run smoother now. :) But I am really
avoiding the boost thing, I usually run the computer display to
indicate remaining range, but for the last few days I've had it on
boost levels all the time.

Wait a minute, I'm beginning to think a bit now about something I
did before I left Cape Town and drove up on Wednesday. A day or so
before leaving I bought some REDEX upper cylinder lubricant which said
would clean the spark plugs and stuff like that. I put some in to the
fuel I had in the car, about 20ml for 20 litres of fuel. That's the
only odd thing I did. I wander if the lubricant has done something
funny. Any ideas on this? Any opinions on using upper cylinder
lubricant? (petrol additive type, I don't really know if one adds other
types to the oil or if upper cylinder lubricant always gets added to
the fuel).

G.
-- 
"a thousand miles from here, there is another person smiling"
1990 Turbo (200T)
name   : gerard van vught
tel    : +27-57-912 2658 (w) / 082 923 9609 (cell)
url    : http://www.acenet.co.za/homepages/gerard/
e-mail : gerard@poboxes.com  / han.solo@galaxycorp.com
         gerard@acenet.co.za / van_vught@frg.issi.co.za