MAC11 help needed

cody at cody at
Tue Sep 2 04:51:02 PDT 2008

It would run better because the arc is using clean, un-used, portions  
of the rotor. You've replaced the cap, but have you replaced the rotor?

It sounds like you have the wires on the right way. #1 wire should  
match up to the rotor tip when the rotor lines up with the little  
timing mark on the distributor body.

  I had a non-turbo 5000 act very very much like what you are saying  
except I also noticed that if I held it WOT it would rev to 3000rpm,  
but then if I turned the screw on the fuel metering plate (CIS) to  
lean it out it would rev freely (but was too lean to idle). I spent a  
bunch of money rebuilding the entire CIS system (**NEW** fuel  
distributor $$) thinking it was in the CIS only to later realise that  
the $7 distributor rotor was bad.

-Cody Forbes

Quoting Rick Houck <rhouck at>:

> 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>
> To: "Rick Houck" <rhouck at>; <quattro at>
> 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
> '86 5ktq - Fast.
> '87 5ktq
> '86 5ktq
> (both non-turbos have moved on)
> Quoting Rick Houck <rhouck at>:
>> 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!
>> _______________________________________________
>> quattro mailing list
>> quattro at
>> ---
>> Watch this space for ads :)

More information about the quattro mailing list