[s-cars] Whacky Boost

[Bruce]

This sounds suspiciously like what happened to me at Virginia Int'l Raceway.

My car was running at full song, then check engine light came on and boost
dialed way back. Then it'd run again but same thing would happen.

Check engine code was for cam position sensor, which we replaced but did not
solve problem. Turned out to be broken key off of crank pulley, which made
ECU not have timing references and it would keep retarding the timing as
boost built, causing it to seem laggy, and then finally throw in the towel
and flash the check engine light until I backed off.

Please note that this problem took two and a half weeks to find, and cost
nearly $500 in diagnostic charges (god bless my extended warranty). Even my
super Audi mechanic was kind of stumped for a while, and went so far as to
consult with other Audi tuners for opinions.

Be careful....if more breaks, you could be looking at real serious engine
damage. He was amazed I did not just break the whole motor. Change the
timing belt while you're in there if that turns out to be the cause.

Let me know if this was the problem...it'd be my first time helping someone
find a real serious problem from my own experience!

Good luck!

Bruce
----- Original Message -----
From: "Chad Hall" <outex at charter.net>
To: <s-car-list at audifans.com>
Sent: Monday, July 08, 2002 3:07 PM
Subject: [s-cars] Whacky Boost


This is a multi-part message in MIME format.
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I am on the list to purchase the MTM stage 1 but currently I'm having
problems with boost that need figured out before the change.  I previously
had a TAP stage 2 with W/G spring that showed 20 psi.  Car felt strong, I
installed a new exhaust (twin 2.5" pipes straight to a Flowmaster) and,
coincidently I think, I began having boost problems.  I had previously
changed to a Samco hose down low, new plugs and plug boots, new PSO, changed
O2 sensor.  I even changed back to the OEM computer and spring--this showed
max boost at 17 psi.  The problem is: under full throttle, say in 2nd gear,
it will pull great then fall back to 9 psi, then back 17 psi, then back to
9, all while accelerating through 2nd gear.  The same thing happens in other
gears.  I have a check engine code that pops up (dealer showed that it was a
cam position sensor code) and I have a new one to install but wanted some
other opinions before I tore into the pulleys.  Am I on the right track?

Chad Hall
'95 S6
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