Re: 5000CSTQ boost Q

[dlawson@ball.com (Dave Lawson)]

As Phil previously wrote,
>b) How warm was the engine - i.e., how _recently_ had it warmed up?
>   Had it just reached a reasonable operating temperature, or had you been
>   driving for a while?  I ask because several MB owners (in fact, all
>   who've tried it) have been able to demonstrate an overboost window
>   just as the engine reaches operating temperature.  Myself, John
>   Robinson and Steve Evans have all been able to reproduce this problem.
>   We suspect an ECU map bug.  In fact, if anyone feels like mistreating
>   their car just once by hitting the loud pedal _HARD_ just before the
>   "N" symbol is reached on the water temperature gauge, we might see if
>   this is common to more than one design.  It happens in all gears.

How appropriate you wrote this today. A few days ago I wrote about
soldering in a new air temp sensor. I followed the wise words from
fellow netsters and soldered my wiring to the short leads I had coming
from the sensor. I was not able to unsolder the flat tabs from the
sensor pins. The panel said it was possibly silver soldered or even
spot welded. Anyways, I got the new sensor bolted back in last night.
Then I went out for a test drive.

Keep in mind that I now have a US single knock sensor MC engine
in my 83 ur-quattro. This engine is similar to the euro MB engine, although
the MB has a 38 hp advantage from the factory, 200 vs 162. With the
WX air temp sensor, the ECU said I had a defective air temp sensor
and turned on the knock sensor light under boost. Also the largest
boost pressure I saw was ~4-5 psi.

As I am out I watch the water temp. It goes up, the thermostat opens
and drops right in to its operating temp. For those keeping notes, I
am using the factory 4 pin coolant temp sensor mounted in the neck
where the upper radiator hose attaches. I ran the sensor gauge output
to a VDO 250 deg F water temp gauge. It probably isn't accurate in
an absolute sense, but for relative comparisons, it works. Anyone
know the resistance curve for the factory coolant gauge sensor?

Back to the test drive... As soon as the temp drops in, I give it WOT.
Knock sensor light stays dark, good. A glance at the boost gauge,
a vac - 15 psi VDO unit, shows almost 10psi. A quick conversion
shown this to be ~.67 bar boost pressure, interesting that the
factory manuals say max boost pressure is .42 bar for the engine
in my car. This is with a stock ECU and wastegate. Didn't hit fuel cutout
either. Maybe a minute later, I go for WOT again, this time I see
6-7 psi. Same 6-7 psi during the morning drive with a well warmed
engine. So chalk up another case of initial warm engine overboost.

When I arrived back in my garage last night, I down loaded the
ECU fault codes, 4444, no errors found. So at this point the engine
is running as the factory designed. Next step, the emissions test
facility, where it will be straped down on a 4wd dyno and see if it
can pass big brothers IM240 BS.
 -
Dave Lawson  dlawson@ball.com
Boulder, CO