Over-boost problem help '88 5ktq

[Nate Stuart]

Some of the  most common failures (in no particular order) are:

1: Torn wastegate diaphragm
2: Split/leaking lower wastegate->intake manifold hose.
3: Wastegate frequency valve circuit error

Answer 1: To test the diaphragm you will need a mighty vac hand pump.
Disconnect the upper (small) hose to the wastegate and fit the pump hose to
the wastegate nipple. Apply a decent vacuum to the wastegate, should hold
with no leaks. I fit does leak the diaphragm needs replacement. To replace
the diaphragm remove the 8(?) bolts on the top of the WG cap and take the
cap off (you may have to disconnect a couple of the electrical connections
on the firewall for clearance). next lift the rubber diaphragm off the base
of the WG assembly. You will need to jam a screw driver down between the WG
housing and the diaphragm plate to keep it from spinning as you remove the
nut holding the diaphragm (this will be quite obvious at this point what is
being replaced). Then installation is simply reverse of the removal.

Answer 2: If all tests above passed then remove the lower hose from the
wastegate to the IM (a bit tricky). Once it's off just go ahead and replace
it the OE hose is cloth covered and hard to tell if it is split, you will
prolly have to cut it off the wastegate side, but you can easily fit a
replacement hose on there and use a standard hose clamp. Re-install the hose
reverse of removal...

Answer 3: If your boost was correct for a given time and it has just
suddenly gone bad w/o and engine bay (specifically any hoses that deal with
the frequency valve) messings, then you can just remove the upper (little)
hose from the WG cap and plug the line (not the wastegate!). Take the car
out for a spin, if this was your problem then you should have a little lower
boost level than normal (~ 1.2bar if you have the stock WG spring).

Answer 3a: If you have mucked about with the little hoses around the
wastegate make sure they are correctly connected like:
http://www.sjmautotechnik.com/ecupic/mcwgdia.jpg

That should cover most of the overboost problems. More thorough info can be
found at SJM's excellent site:
http://www.sjmautotechnik.com/10vwaste.html#wgcnt

Later!
-Nate
'89 90tq
www.newtsplace.com/90tq

----- Original Message -----
From: "Britt Crowell" <britt at fortcollins.com>
Subject: Over-boost problem help '88 5ktq


> Ok I'm having an overboost problem with my '88 5ktq, I have a chip in it
so
> it will pull 1.8 bar. Now I'm starting to get an over boost condition.
Where
> should I start looking. Seems all I can find in the archives is low boost
> problems, so I guess I'm lucky my car just wants to go faster, but that
fuel
> cut out is just a real drag! Any help or links would be great.