By: John Anderson (From MOTOR, February 1990, Vol. 173,No. 2)
Well, was I rummaging through some old mags getting thrown
out at engineering and what should be on the cover of the
February 1990 issue of MOTOR but a color cutaway of everyones
favorite supercharging device. Now the mag is dedicated to
auto service technicians and presents a lenghty discussion of
potential problems so I thought I'd describe the major points.
The article also babbles about Fords T-bird blower which I'll
leave out.
Prime directive for servicing is cleanliness plus hose and clamp
maintenance. Air filter clean and intake tract free of debris.
VW says make sure absolutely no leaks on the intake side which will
suck in dust and kill the unit, with scroll/displacer tolerance a
tenth of a millimeter, this is of prime importance.
Leaks will cause whistling sounds, after inspecting the plumbing
do the basics, good spark, hardy fuel pressure (? pump fails often
thanks VW), tight vacuum lines, etc. The G60 uses a bypass valve
mechanically linked to the throttle valve to reroute uneeded boost
back into the supercharger at low rpm, reducing parasitic drag. As
the throttle opens, the valve closes off the return line to the
G-lader and the engine gets full intercooled boost (11.64 psi). When
the throttle closes, the bypass opens, at idle the G60 gets all the
boost blown back into it's intake. In the case of low boost, check
the bypass valve adjustment (factory set, consult a manual) minimum
must be 8.73 psi, if everything else is in order and you can't get
8.73 psi, REPLACE THE G60. VW says don't bypass the valve for more
low end oomph, if its closed all the time, the engine would be really
jumpy and get poor mileage (sticking or seals defective a possible
problem?)
Furthermore the Idle Stabilizer Valve (ISV) performs another
function on the G60, at max boost it opens bleeding excess pressure
back into the intake side of the G60 as well. The SAME THING OCCURS
WHEN THE KNOCK SENSOR DETECTS DETONATION (or other sounds?) AND THE
DIGIFANT SYSTEM CAN'T COMPENSATE BY RETARDING TIMING ALONE!! Essentially
a wastegate in function at full boost the ISV also maintains even performance
between different vehicles preventing one Corrado from being faster
than another. OBVIOSLY A ROUGH IDLE COULD RESULT IF THE ISV GETS STUCK
CLOSED ALSO OVERBOOSTING THE SYSTEM (SLIGHTLY BUT NEVER OVER THE 14.55
psi MAX WITH FACTORY PULLEY RATIOS). VW claims you'd never see a stuck
ISV, new plunger design blah, blah, blah, etc. (Funny I think the '90
Passat of my mom's uses the new style valve, not the rotating one and it
did get stuck once, but I could be wrong about it's type). NOW FOR REAL
INTERESTING STUFF, the DIGIFANT SYSTEM CONTROLS THE ISV BY READING THE
ENGINE LOAD AND BOOST PRESSURE WITH ITS OWN SENSOR (UP THERE ON THE BLACK
BOX, WE'VE ALL SEEN IT) THE SENSOR REPLACES THE AIRFLOW METER AND IT HAS
!!!NO TEST PROCEDURE!!! (mag insults VW's confidence in a snide manner).
It further notes the line from pressure sensor to manifold is a speciffic
lenght (1.0 meter) and must be so because you can screw up performance
by installing a different length as the pulsations of air in the hose
(harmonics) would hit the sensor out of phase and cause problems. Specifically
ECU out of phase readings will make improper engine adjustments and cause
drop in perfromance!! Now I had noticed Bentley specifically tells you
this hose must be replaced with the proper one from VW (why they simply
didn't mention the length requirement is beyond me) furthermore a guy
at the local garage told me they had been having trouble with the hose
leaking after time and said replacement might solve some problems which
I did not but now will do, maybe there was a TSB on this, I glanced over
my list briefly and didn't see one but am note sure.
Anyway the article goes on to tell you that oil changes are fairly
important and that one should always note that if the oil feed line needs
replacement it is a very special and particular size. Furthermore it says
rebuilding will not ever be possible and parts including the small inner
driving belt will not be available. Goes on to say service is quite simple.
The cutaway dwawings are really cool as is a series of pictures showing
how the scroll charger compresses air.
Well if this info has been noted anywhere before, I'm sorry for the
inconvenience, if not I suggest every G60 owner try to find a copy and
give it a look. Again the article is in MOTOR, February 1990, Vol. 173,
No. 2. The article really gives a number of good ideas IMHO.
John Anderson
ja@coe.wvu.edu
'71 Westy, '90 G60
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