1987 Audi 5000cs low boost

Bernard Littau bernard.littau at gmail.com
Fri Jan 17 12:37:18 PST 2014

If you are running the stock wastegate spring, 4 pounds of boost is what the
system makes without any computer augmentation of the boost.

You may be leaking boost, or have a stuffed up exhaust truly preventing more
boost, as has been pointed out, or you may not be augmenting the boost.

As far as augmenting the boost, the reasons are physical or electronic, for
lack of better terms.  Does the waste gate work physically?  Is the membrane
inside the wastegate torn?  Are the vacuum hoses all good to the wastegate?

On the electronic side, is the ECU attempting to augment boost?  This can be
tested with a 12V LED run in series with the Wastegate modulator.  Run the
LED into the car, and watch for it blinking when you should be making boost.
Watch the polarity (try it both ways if you have to).

If the LED blinks, the ECU is actively trying to augment boost.  You have a
physical problem.  No blinking (if you did it right) means ECU has an issue
with engine temperature, air temperature or whatever else.

Another thing I have done is run the lower wastegate inlet into the car and
pull a vacuum on it with a hand pump.  If the physical stuff is all working,
you should get massive boost.

It has been 10 years almost to the day when my '88 5ktq was replaced by a
Sienna, I'm a bit fuzzy on the details of the boost system.  Cross check
what I have said :-)  At least it gives you some direction, I hope.

Woodinville, WA
'88 5ktq RIP

-----Original Message-----
From: quattro-bounces at audifans.com [mailto:quattro-bounces at audifans.com] On
Behalf Of Nick Lawrence
Sent: Friday, January 17, 2014 11:26 AM
To: quattro at audifans.com
Subject: Re: 1987 Audi 5000cs low boost

A couple of easy places to check for a big boost leak.....
The "michelin man" hose, feel the underside for soft spots, take it off and
inspect the umps and creases for a split.
The hose at the right end of the intercooler, reach down from above and feel
around the underside of the "bulge" that allows for movement.
And on the later MC turbos there is cylindrical sponge the gets out of place
and blows into the intercooler inlet,  very hard to see.

On 1/17/2014 9:20 AM, Eric Huppert wrote:
> Been all through sjms low boost checklist and I still only make 4 psi 
> boost. Anyone ever had a problem like this where everything checks out 
> and still super low boost? Any ideas would be greatly appreciated
> Sent from my iPhone
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