MAC11 help needed

Paul Heneghan paul at
Tue Sep 2 00:56:16 PDT 2008

I had an old Audi 100 (non turbo) that exhibited similar symptoms - no
power, not revving past 3000, etc.  Turned out to be a sheared/disintegrated
key on the crank pulley.  It meant that the valves were a few degrees off
relative to the crank, so no amount of fiddling with distributor position
would get it to run properly for any length of time.

I now replace those crank pulleys when I do the timing belts.


-----Original Message-----
From: Ben Swann [mailto:benswann at]
Sent: 02 September 2008 02:54
To: rhouck at
Cc: 'Ben Swann'; quattro at
Subject: MAC11 help needed


That sounds like a bad signal from the O2 sensor - your mixture is off.
Timing should
not be a problem unless pushing the envolope of performance - that is not
happening at
low boost and RPM. Also I read you may not be using CIS for fueling and that
may change
some things - big time!

With MAC-11 ignition - if the car starts and runs, then it will run until
high RPM
unless bad rotor/cap/coil misfifre/bad wires, etc.  I'd be looking at the
fuel side of
things right now unless the ECU is competely hosed.  If you have the engine
started and
running through 2000 RPM the should continue to do alright to 6000+ RPM if
essentials are in basically good working order, then  Don't get sidetracked
by your
hypotheseis below - BTDT.  It is possible that the coil trigger signal to
the EFI is
off, but not likely either.

BTW what is the fuel delivery to the EFI - I have been struggling for about
2 years to
get mine straigh - using Megasquirt, but expect same sort of operation,
especially as
RPM increases.  The CIS pump/tank setup on my UrQ is not proper for an EFI
setup -
cavitation problems due to lower fuel pressure setting with EFI than stock
CIS.  I am
fairly certain of this after much trouble-shooting and analysis    I suspect
4000 Q is

I believe my ultimate solution is an in-tank pump or pre-pump with surge
tank to main
pump solution.  If someone knows differently - I'd sure like to know.  In
fact am
looking for an interim solution for a pump that is designed to operate at
between 35 and
60 PSI rather than above 60 PSI as for  CIS.

Suspect this will evolve into different thread - if so change the subject
line please to
something like "Fuel delivery for CIS to  EFI conversion".


[Date: Sun, 31 Aug 2008 19:00:06 -0400
From: "Rick Houck" <rhouck at>
Subject: MAC11 help needed
To: "Quattro List" <quattro at>
Message-ID: <003101c90bbd$4f7d3560$6401a8c0 at rick>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";

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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