MAC11 help needed

[Rick Houck]

Cody,

I get your point about not really changing the timing. Guess my description 
was not accurate. Testing had confirmed to me that the hall sensor is used 
only for starting, as you say, but why would it start running better when I 
rotate the distributor counter-clockwise maybe 30 degrees or so? In fact, I 
was surprised how far I could turn it and still have it idle well. Could I 
have my wires on in the correct order, but not indexed properly?

I have the #1 plug wire on the cap over the rotor tip as it is aligned with 
the distributor mark and the cam and crank are on their TDC marks. I did 
re-index the wires to test that theory, but I wonder if I went the wrong 
way? It is in the first of the two tall plug wire sockets as you go 
counter-clockwise. I replaced the distributor cap at the track with a used 
one I had, then installed a new Bosch, then tried another used with its 
wires. After the original one, I just followed the same pattern on each one, 
so if I got it wrong the first time, then they have all been wrong.

Remember, the car had been running fine, then started missing occasionally, 
then getting worse until it won't rev up to 3000 RPM. Keep your ideas 
coming. I'm sure it is something simple that I am overlooking, but it seems 
I have tried everything related to the ignition system.

Rick

----- Original Message ----- 
From: <cody at 5000tq.com>
To: "Rick Houck" <rhouck at neo.rr.com>; <quattro at audifans.com>
Sent: Monday, September 01, 2008 11:32 AM
Subject: Re: MAC11 help needed


Here's one problem with your theory of advancing the ignition timing:
turning the distributor does **NOT** change the timing on an MC
engine. The ignition timing is done by the ECU with data collected
from the flywheel sensors. You can't change it without a chip, period.
The hall sensor in the distributor is used only once to determine
which stroke the engine is on during cranking, then once the engine
knows where cylinder #1 firing stroke is it uses the 2 flywheel
sensors and math to figure out the other 4 cylinders and skips over
the TDC flywheel pin every other time it passes by. This is why it
won't start when you turn the distributor - during cranking when it's
looking to find when the hall sensor lines up with the TDC pin it
simply never happens and the ECU never finds cyl#1 TDC so it never
starts firing the ignition.

When you turn the distributor while it's running you are moving the
alignment of the distributor cap VS the rotor and creating a "new"
place for the arc to jump. Sounds to me like you should replace the
cap and rotor.

-Cody Forbes
http://www.5000tq.com
'86 5ktq - Fast.
'87 5ktq
'86 5ktq
(both non-turbos have moved on)


Quoting Rick Houck <rhouck at neo.rr.com>:

> 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,
> Rick
> Pulling my (gray) hair out!
>
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