New problem with the 200t ... overboosting and WGFV testing... (long)

[Gerard <gerard@poboxes.com>]

Hi!

Thanks for the help on the overboosting problem on my 200t. Not that
it is solved though, it still overboosts at altitude, but the help
from the list has assisted in getting more info on the problem.

Last night and this evening I did the following tests to the WG and
the ECU controlled FV:

	1. Removed FV to WG air duct, clamp off FV duct and leave
	   the WG connection open to the atmosphere as was suggested
	   in the "WGFV test procedure" thread. Test boost under this
	   condition.

	2. Reconnect the FV to WG line and test boost under this
	   condition to see if overboosting still occurs easily.

	3. Additional procedure: leave FV to WG air duct in place,
	   remove 2-prong electrical connector from the FV housing.
	   Test boost under this condition.

The results for the 3 situations were as follows:

	1. With FV-WG line removed the only boost assist is from the
	   WG spring and atmospheric pressure (about 0.8 at this
	   altitude). I warmed the machine up and then hammered the
	   throttle. The boost takes more effort to reach the max
	   set by the spring, which is 1.4 bar on this car. At 1.3
	   bar the car tends to "fluff and flounder" a bit. Pushing
	   harder will get it to 1.4 bar. With the FV-WG line removed
	   the boost never went over the 1.4 bar. This was to be
	   expected as there is no assist from the ECU controlled FV.
	   The car is "less drivable in this state". I think it is
	   the WG which is opening slightly at the 1.3 bar that causes
	   the bit of fluffing in the drivability.

	2. With the FV-WG line back in place the overboost happens
	   again. I can easily get to 1.4 bar even below 4000RPM
	   and under 120km/h and with about 1/2 - 3/4  throttle.
	   At this point the boost seems to be easily assisted by
	   the ECU and it heads merrily for 1.6 bar, ie. the cutoff.
	   Under this situation with the FV-WG line back in place the
	   car is more drivable across the rev range with no fluffing
	   or hesitation up to and beyond the 1.4 bar limit and up
	   to the 1.6 bar cut-off. As far as I see it the boost assist
	   works in this case.

	3. With the FV-WG line back in place, but with the 2-prong
	   electrical connector removed from the FV housing (ie. the
	   ECU cannot inform the FV to open or close at any boost
	   level) the boost will easily go to 1.4 bar and head over
	   that to 1.6 bar. To me it seems the FV is stuck permanently
	   open, this would not be noticed in #2 above, but I think
	   this test combined with results of #1 and #2 will indicate
	   that it might just be stuck or bust.

Approximately a month ago I checked the FV-WG air line and it was
ready to crumble into dust so I replaced it with a stronger piece of
Goodyear fuel/emmission grade rubber tubing. This resulted in better
drivability and boost control of course, but even in that case I never
had the boost level go over 1.1-1.2 bar up here where the atmospheric
is 1.4 bar. I need to know whether a turbo setup to produce 1.4 bar
of boost will produce less boost when the atmospheric pressure is
lower. I mean, is the spring that holds the WG down setup at the coast
to provide 1.4 boost with atmospheric pressure assist at the coast?
Is it designed to provide 1.4 bar boost under any atmospheric pressure?
My suspicion is that atmospheric pressure plays a role in when boost
is released, but I haven't got any more detail on this from the list.

If boost is released sooner at lower atmospheric pressures then how
does one explain my turbo getting up to 1.4 bar boost (case #1 above)
at an altitude where atmospheric is 0.8 bar?

I thought that the max boost and assistance were to be had at the very
edge of the operating conditions, ie. you're asking just about
everything from the car. But it doesn't take much (under 4k RPM,
3/4 throttle, under 120km/h) to force the cutoff to happen.

Under what conditions through the rev range will the ECU signal the
FV to open? Is the FV a open/close type or can the ECU open it
gradually? I think it is the open/close type.

I guess if the FV is faulty then it could just be that the ECU hasn't
been asking for overboost, it is just happening naturally. I guess
the next test is to go through the list and find out about those
diode connectors people were speaking of that connect to the 2 prong
connector on the FV and will indicate when the ECU asks for overboost.
If it doesn't ask for it, but the boost goes into the overboost
region then the FV is definitely shot.

But why is boost all of a sudden building to 1.4 bar naturally and
so quickly when it has never done it before? If at some point I
did something to push the car hard (ie. going passed some truck)
and at that point something went wrong that caused the turbo to
build boost so quickly to 1.4 bar at altitude and the ECU thought it
time to add extra boost assist, then could something have failed in
the FV and have buggered it up? But the question still remains why
the turbo builds boost so damn quickly now whereas it never did it
before? The only things I did were between the machine reading normal
boost (last year) and it suddenly performing this overboost thing,
where:

	a) go to the coast for 2 weeks, only saw 1.3 bar under heavy
	   conditions
	b) put in REDEX upper cylinder lubricant into the fuel 2 days
	   before the return journey
	c) held a constant 160km/h speed for most of 1300km of return
	   journey from the coast to here. The weather was somewhat
	   wet, the car felt like it was lurching a bit, but I've
	   put this down to having to have my plug leads replaced as
	   it will only happen in wet weather

The next questions are:

	a) is a stuck WGFV repairable?
	b) is so, how can it be checked and repaired?
	c) is this going to be a complete replacement job?

Oh yes, one more question, what voltage is applied to the 2-prong
connector on the FV? Which prong is +ve and which is -ve?

I'd appreciate all the help I can get. :)

Thanks.

G.

PS: I know my future holds a ECU mod to get higher boost, so some
    might be wandering why I'm complaining about this overboost thing,
    but obviously this thing that is happening now is not "natural",
    so it is best first to make sure the car is operating properly in
    its stock form before doing anything new and different. And this
    thing is definitely not doing stop operating, if it did then I'd
    be very ashamed to drive such a dangerous vehicle that will cutout
    when overtaking something and the speed and throttle position are
    nowhere near max!
-- 
"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