MAC11 help needed

Rick Houck rhouck at
Mon Sep 1 19:52:06 PDT 2008


No vacuum leaks detected from my pressure test of the complete intake 
system. I have tried different torques on the original and spare knock 
sensors with no change, but they are used, not new, but from decently 
running cars. Thanks for your reply, but I think it must be something else. 
Keep your thoughts coming.

----- Original Message ----- 
From: "John Lagnese" <jlagnese at>
To: "'Rick Houck'" <rhouck at>; "'Quattro List'" 
<quattro at>
Sent: Monday, September 01, 2008 2:32 AM
Subject: RE: MAC11 help needed

Knock sensor correctly torqued? They crush easily. Is ther a vacuum leak,
like a hose not connected?

-----Original Message-----
From: quattro-bounces at [mailto:quattro-bounces at] On
Behalf Of Rick Houck
Sent: Sunday, August 31, 2008 7:00 PM
To: Quattro List
Subject: MAC11 help needed

patient is coupe quattro conversion (dedicated track car) with 10v turbo
(MC1 w/one knock sensor) motor. I can get the car started and running up to
2000 to 2500 RPM before it starts backfiring. Can hardly get up to 3000 RPM
even with throttle floored. The flywheel "0" mark, the cam mark, and the
distributor mark all line up properly. If I move the distributor off the
mark (advance) while running, it will rev like normal, but won't start after

shutdown. I can move the distributor back to initial position and it starts
right up.

I suspect that something is causing the timing to retard, but I have swapped

out the ECU, complete distributor, the cap and rotor, plugs, wires, RPM and
flywheel sensors. I plan to try another knock sensor, but can't figure
anything else that would cause a properly running engine to start backfiring

like this. BTW, after the problem, I took the opportunity to install my
newly rebuilt engine, and the problems are the same, so I can rule out
mechanical issues.

I have been using the 034 Motorsport EFI, and there is no sign that it is
going lean or rich when this occurs. My fuel pressure (aftermarket FPR)
rises slightly as revs come up as I would expect with the start of boost.
Besides, the timing seems to be the thing that has changed, as evidenced by
the regular running after advancing timing.

It acts as though the timing reference pin is in the wrong place, but it has

been running fine for 8 years and the problem came on gradually during some
rainy sessions at Watkins Glen in May. Thought something must have gotten
wet, but after swapping everything I can think of, nothing has changed.

The pin is still on the front side of the flywheel, but it does not line up
with the pickup when the crank is at "0" and the distributor and cam marks
line up. Is this right?

Any help appreciated,
Pulling my (gray) hair out!

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